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ZIP & SIS – Multi-Functional Sheathing

by Chad Ludeman on May 3, 2010 · 42 comments

in envelope,materials

If you’ve been following us for a while, you probably know we’re big fans of building products that serve multiple purposes. Today we look at versatile sheathing products that go beyond simple structural support and contribute to the “Hybrid Prefab” method of building that we continually strive for. We’ll take a look at two products: Huber Engineered Woods’ ZIP System and DOW’s Structurally Insulated Sheathing.

ZIP System Sheathing by Huber Engineered Woods

The first product, ZIP System Sheathing, acts as (1) a structural sheathing and (2) a Water-Resistive Air Barrier in one product. You can see in the image below that we are using this on our current Skinny Project. The product consists of two different structural panels (one for the roof and one for the walls) that is coated in a liquid applied WRB (Water Resistive Barrier) on one side. The wall panels are green and the roof panels are a copper color. The system is completed by a proprietary butyl tape for the seams that makes the entire assembly water and air tight.

Skinny with Windows

We decided some time ago that we would start taping all exterior seams in our OSB sheathing to improve the air-tightness of our homes in the quest to reach the illusive 0.60 ACH @ 50Pa that accompanies official Passive Houses. The ZIP system was the next logical step that allows us to eliminate the step of installing an additional building wrap this is prone to leaking anyways. The ZIP system adds a few hundred dollars to our overall cost that we most likely would be spending anyways on a better butyl tape to stick to unprimed OSB as well as a better WRB than Tyvek. Using ZIP allows us to completely eliminate this step, saving us time, money and aggravation. The framing crew couldn’t be happier either as they hate installing building wraps. We’ve included some geek specs for you below.

ZIP Geek Specs:

Assembly Air Infiltration: 0.0072 cfm/ft2 @75Pa
Assembly Air Infiltration: 0.0023 cfm/ft2 @75Pa
Permeance: 2-3 Perms
Recognized Water Resistive Barrier
ZIP System Tech Docs

SIS (Structurally Insulated Sheathing) by DOW

The next product is similar to ZIP in that is acts as both a (1) structural sheathing and (2) an airtight water-resistive barrier, but it adds (3) exterior insulation to the mix as well. The DOW SIS product is made up of a thin structural element that looks a bit like particle board, a layer of rigid Polyisocyanurate insulation (think closed cell spray foam) and a blue top layer for improved water resistance. The product comes in a 1/2″ thickness that is rated R-3 and a 1″ thickness that achielves R-5.5. Once installed, using DOW’s Weathermate Tape will give your building envelope an airtight WRB that is ready to clad.

What’s great about the DOW’s SIS is that it can create a continuous layer of external insulation on your building which is pretty much the most effective way to completely eliminate thermal bridging in your exterior walls. This continuous layer of insulation is already required by building code in Canada and some northern US states (I believe). It may not be long until the entire US building code starts requiring this and what better way to achieve it than with a product that actually reduces overall labor?

SIS Geek Specs:

Panel Air Infiltration: 0.05 cfm/ft2 @75Pa
Panel Air Exfiltration: 0.1 cfm/ft2 @75Pa
Permeance: <0.3 Perms
Recognized Water Resistive Barrier
Water Absorption (% by weight): <9
DOW SIS Tech Docs


So which product is best and should you consider using either on your next building project? If you are not using one of the prefab wall systems like SIPs or ICFs, then we would highly recommend incorporating one of these hybrid sheathing products into your designs. Both are carry premiums in materials price, but it’s really not a bad as you would expect once you factor in the improved building performance and reduced labor from skipping the building wrap application. I know we were expecting higher prices than we got back from our material supplier on Skinny, Shelly’s Lumber.

If air sealing is a top priority in your build, then most building wraps are just not doing that great of a job unless they are applied to meticulous commercial standards. The wrap is often tearing or pealing off in sections. Almost no one tapes all seams as directed and the installers punch hundreds of tiny holes in them when installing with a slap stapler. Using either of these products to achieve an airtight home is also going to improve the performance of any insulation installed within the wall cavities. Air infiltration, especially in fiberglass insulation, can decrease the effective R value of the insulated wall by 15 – 40%. Most homes in the US could reduce their utility bills by 30% if they used one of these products from the beginning.

Of the two products, we’re looking pretty hard at the SIS for the future. It will add a few hundred dollars to each home compared to ZIP, but we will gain continuous insulation on the outside of our building lot footprint. In other words we are gaining free real estate for our wall insulation that does not decrease the interior square footage of the home with a thicker wall. The cost is also far lower than having an insulation contractor come in and spray an inch of close cell spray foam on all of your walls. The only downside is that it only comes in a 1″ max thickness. Most of the US requires 1″-2″ thicknesses of exterior insulation in order to eliminate condensation concerns in the  walls. We are much closer to 2″ in our climate.

Whatever you choose. seal it well and insulate the heck out of it. We hope this post helps in your decisions making process.

If you enjoyed reading this post I can promise you'll love our new writing over at Postgreen Homes. Yeah, we know that's the same thing your favorite band said and their new album is nowhere near as good as their early stuff, but seriously, we are actually still getting better.

There also isn't much conversation to be had here . . . at least not with us. So come on over to the Postgreen Homes Blog and tell us what you think of our new(ish) digs and crazy ideas. We will be sure to tell you what we think of your opinion.

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A Few Framing Details from the Skinny Project
May 3, 2010 at 3:50 pm


1 Lloyd Alter May 3, 2010 at 5:23 pm

I have been learning a lot from Alex Wilson at EBN and there is a lot not to like about Styrofoam. I did a summary of the problem in the link above, but we really shouldn’t be using products made with fire retardants like HBDC. If you can ZIP it up, it is probably better.

I live in Canada and they have been using Styrofoam as structural insulated sheathing forever. I have never been comfortable with the idea that a sheet that I can break in my hands is strong enough to act as structural sheathing. They may have the numbers but it just isn’t intuitive. The doors on my own cabin in the woods up north don’t shut properly because I was insufficiently concerned about lateral bracing and racking, and here we are relying on a sheet of styrofoam? Not me.

2 lavardera May 3, 2010 at 9:43 pm

two questions/comments

• If these products don’t act as a nail base then your siding fastening must correspond with your stud-work. And anything else you might hope to fasten to a facade has to be thought out.

• I like the idea of eliminating wrap from a labor standpoint, and because of the obvious holing of the tyvek wraps during install. But at the same time wraps, and in the past building paper – or tar paper was the first line of flashing when various claddings went on the house. Traditionally everything went on in layers, each shedding water from the ones below. I don’t see these sheathings being able to perform like that and it worries me.

3 Chad Ludeman May 4, 2010 at 8:52 am

Two of our most informed architect readers don’t like aspects of these products. Let’s see if we can further the discussion a bit.

Lloyd – Without doing more research, I’m a bit confused as to which type of foam is no good. Are you saying that all EPS, XPS and Polyurethane foams are no good in your book? If that’s the case, many builders are in for trouble. What would we use under our slabs and basements? Most commercial exterior insulation details would be thrown out the window.

Also, I think we are talking about two different products. The SIS has a structural component to it and is not simply a sheet of foam. You would not be able to easily break it, and it strengthens a home just as well as OSB. People do use foam only, but they have to do extra structural bracing in their framing like putting OSB on the corners for at least 4′.

We are certainly not claiming that either of these products is the greenest product with no fault whatsoever. We don’t really think there is such a thing as the perfect green product, so we try not to get into bashing products people are trying to use as they work hard to build more energy efficient homes. Sorry vinyl, we will make exceptions to bash you. I personally don’t like close cell spray foam too much, but there are a lot of good designers and builders out there using it very effectively to reduce their buildings’ energy consumption over the life of their projects.

To date, we haven’t gotten into total carbon footprints of products, systems or entire homes. I think it’s mainly because we don’t feel we are experts on the subject (yet) and would be better off leaving the discussion up to those that are well versed in it for now. Your not talking about carbon though, so I would argue that a product that may have harmful chemicals in it should not be open to the homeowners. Any rigid foam we use and most other use is not. This sheathing will be covered by cladding and other rigid foams will be either underground or behind drywall. From what I’ve read in your links, I’m not too concerned with our details. I don’t have a subscription to the other sites to dig deeper into their arguments at this time.

Greg – We use a rain screen detail on every home that requires furring strips to be fastened to studs that will then act as our nailing base. This is needed to matter what type of sheathing we use.

In terms of the lack or building wrap, I’m not sure what to say. We have seen countless studies that show that building wrap is pretty much worthless. The ZIP has a premium liquid applied WRB on it that you could argue is commercial grade. There is no question that the butyl tape is sealing the seams that might be the only question mark on this system. The SIS also has rigid foam that is inherently a WRB and air barrier. Again, the Weathermate tape from DOW does a very convincing job of sealing all seams.

Don’t take our word for it. Take a look at what the Building Science Corp has been doing for years. They are putting 4″ of rigid XPS on many of their homes with no additional building wrap. Those guys are designing and building some of the best energy efficient homes in the US with solid supporting documentation behind every detail.

4 Chad Ludeman May 4, 2010 at 9:05 am

Not sure how I forgot to address alternative green insulation products. Are there alternatives to rigid foam that may be better for the environment? Absolutely. These products also happen to cost much more and are not readily available. Even if you had the budget for them, it would be a logistical nightmare to source them for the average project in the US.

We try to balance the green and affordable here. If a product is ultra cheap, but clubbing baby seals for recreation, we try not to use it. If a product is injecting life back into our planet in its sleep, but murdering our bank account, we also try not to use it. We’re trying to prove that green building can be affordable and that every builder, from small custom to high production, should be jumping on the wagon. These two sheathing products can be used by any builder with known, minimal costs to their bottom line. The others simply can’t.

Imagine what the impact on this country’s energy usage would be if all production builders used either of these products instead of simply slapping up OSB sheathing with no building wrap and no taped seams? We’d be shutting down at least 50 of our worst polluting coal plants for starters.

I also added a better image of the SIS at the bottom of the post so everyone can see the structural portion, the rigid foam and the blue WRB top layer.

5 Lloyd Alter May 4, 2010 at 9:44 am

EPS and XPS foams all have HBDC in them. There is no reason to have a fire retardant in a foam that goes under a slab in the basement, but the manufacturers don’t bother to produce it. I suspect that they will once the Europeans ban the stuff. Polyurethane does not have HBDC.

With respect to the exterior sheathing, I misunderstood the product and withdraw my complaint about its strength.

6 lavardera May 4, 2010 at 10:24 am

Chad, understood that you are fastening cladding on the furring/studs. There is nothing wrong with that. But it takes a degree of precision in that your studs have to fall exactly on your cladding panel joints if you don’t want to end up with a lot of waste and trimming of the panels. This is all great with a highly managed project like yours. My fear is that with most builders it could progress to compounding mistakes in spacing that could waste material, create unexpected hours, and not to mention spoil a carefully composed facade. I like things to be more error tolerant and I see things that are as more likely to gain wide adoption.

I agree with you that these products will make a better air seal. House wrap, and the building paper that came before them – like you say they really did not do this well. But these are two different products. This is a cladding + air seal. Building paper is at best a draft blocker + flashing. My concern is that while you have greatly improved the air barrier you have completely dropped this line of flashing. How do you get that back?
For instance I’m guessing your rain screen has flashed horizontal joints like the 100/120k houses. The top of that flashing has nothing to lap behind so it only protects the joint – it does not serve to move water out of the cavity. Any water that finds its way in has to travel all the way down to the bottom of the cladding where you will have a place for it to exit. All that way down its going to encounter horizontal tape joints and unless that tape has a perfect seal to the sheathing panel the water is going to want to get behind that tape.
Do not like…!
Not trying to be alarmist. There would be no great quantity of water in that cavity. It will be fine. But we should also be cognitive of when we are abandoning sensible principles of construction and relying on tape and glue.

7 Chad Ludeman May 4, 2010 at 12:30 pm

Now we’re getting somewhere. The SIS product does use the closed cell poly foam, so hopefully it doesn’t have the nasty stuff in it.

I see your points Greg. Furring is definitely not a piece of cake, but not overly difficult for most crews. It adds cost and labor, but you can always run furring systems both vertical and horizontal if more attachment points are needed. I’ll still take the combo product and tapes seams any day of the week after researching and seeing how most homes are wrapped in the US. I’ll take an engineered product any day over thousands of tiny holes and tears in my building wrap that is covering untreated OSB… We can agree to disagree for now.

8 lavardera May 4, 2010 at 1:40 pm

I don’t disagree, not at all. You can’t achieve the tight construction you are after with tyvek house wrap. And building paper never was meant or even presumed to do that. But I’ve seen other new approaches go down in flames because water got past them.

Question – how are you detailing your window jambs relative to the rain screen cavity. Most American windows are designed to mount against the sheathing, and extend enough for siding and trim to butt into the side of their frames. When you add the depth of the furring cavity with siding over it you can be out past the front face of the window. If it is you have to be sure you don’t let a lot of water into the cavity around from the joint around the window. Without any flashing lap of a building paper or wrap layer how do make sure this sheds water?

And maybe I’m too worried about the difficulty of others executing the furring + siding. But I see the status quo of vinyl siding and vinyl windows out there. I’d like to see good sustainable practices to supplant these, but I know they have to be dumb simple.

9 Garret May 4, 2010 at 1:50 pm

I am interested in what solutions you have fiddled with to deal with one of the asserted downsides: “The only downside is that it only comes in a 1? max thickness. Most of the US requires 1?-2? thicknesses of exterior insulation in order to eliminate condensation concerns in the walls. We are much closer to 2? in our climate.”

Is one option another layer of XPS outside the SIS with taped seams and joints?

Interesting products. Wonder how they would work in retrofit installations.

10 Chad Ludeman May 4, 2010 at 2:26 pm

Garret – Yes, that is exactly what we would look to do.

11 lavardera May 4, 2010 at 3:49 pm

reviewing the sites for Zip and SIS myself:

The ZIP is essentially an OSB panel with a vapor permeable air/water barrier applied. This should have no problem accepting fasteners whether on stud or not.

The SIS is less clear in this regard – it is using a thin layer of OSB to provide strength covered by closed cell foam and a air barrier coating. So it has some strength – enough to hang siding from I’m not sure.

Also I could find no mention of the vapor permeability characteristic of the material. I would suspect it would be vapor permeable for use in winter climates – it should be. But closed cell foam does not speak permeable to me. This is also a concern with other exterior foam insulation layers, particularly if you are going to tape them. If the foam will not “breath” and you tape the joints you are making a recipe for trapping moisture inside the wall. The place to make your tight air seal is on the inside of your insulation.

12 Chad Ludeman May 5, 2010 at 7:11 am

Greg – I actually have the perm specs of both products in the post. You are correct in that the SIS is impermeable and the ZIP is semi-impermeable. I state that 2″ is needed due to the moisture issue you mention. I’ll probably have an entire post dedicated to this issue in the future. Basically, we need 2″ here to keep condensation from forming inside the wall. Then the drywall layer can be air tight, but still vapor permeable to allow any moisture in the wall to dry to the inside. Ideal? Probably not, but show me the perfect wall for our climate and it will probably cost a fortune to build…

13 lavardera May 5, 2010 at 8:59 am

I understand where you are going with this – thicker exterior insulation moves the dew point into the foam insulation layer, which with its impermeability will never admit water vapor to the location where it would condense. Thats great, and it protects your wall system from leaks of warm moist air from the interior. The air coming from the outside is not a worry, as its cold and dry, and the further it moves into a warm wall system the more moisture it can support and actually carry out of your wall.

And this is the crux of my problem with sealing on the outside. Condensation from warm interior air is not the only potential source of moisture in your wall system. Windows, doors, roofs, poor flashing conditions and any number of small failures can let water into your wall. Once you make a tight air barrier with exterior foam insulation and taped joints that water and the vapor you want it to turn into as it dries has no way out of the wall. You have vapor barrier towards the interior, and you have impermeable foam and taped joints towards the outside. This is exactly the condition you don’t want to create. Compound that with the lack of flashing layer from omitting the building paper and you may have conditions that are more likely to admit water behind the foam where it can’t get out. That wall system is intolerant of any failure and is a recipe for mold, and eventually rot.

Without getting into specifics that would make this post even longer I would say that you should leave your foam untaped so that water vapor can at least travel between panels, and that you use an air/water barrier layer that contributes to flashing the wall. Make your vapor tight seal at the inside of your wall only.

That said I really like the Zip product but I’m not convinced that the tape will perform in the long run. You won’t really have an answer to that until you open up one of these walls in 60 years and see if the tape is still sticking. Glues tend to loose their volatiles and their stickiness along with it. If the tape is more of an uncured butyl strip – akin to the uncured rubber membranes that are used for waterproofing below grade and for ice damns on shingled roofs, then I’d say – yes, I think it will last. But one last caution is I would expect the Zip and their tape are not UV durable – meaning if used in an open joint system where they are exposed to sunlight they would degrade and eventually fail.

14 Chad Ludeman May 5, 2010 at 10:33 am

Greg – I think you are misunderstanding the intended wall detail. The exterior insulation is the air, water and vapor barrier. The interior drywall layer is an air barrier only. It is NOT a Vapor Barrier. There is no layer of poly or anything like that on the inside of the wall. The wall WILL dry to the inside.

Again, please don’t take my word for this. Many experts across the US argue about the very same thing we are discussing all the time. I would start with the Building Science guys. You probably have one of their books in your office. Builder’s Guide to Cold Climates or Mixed-Humid Climates most likely. If not, I would buy one. We have their SIPs book which has a lot of great details as well.

Also check out GreenBuildingAdvisor examples. Here is a link to a video using 4″ of exterior XPS on a building. There are a bunch of great videos here.

As for your concerns on the ZIP Tape, I’m not sure what to say. I think I could tear apart Tyvek a bit easier. IF seams are even taped, why would their tape not also fail? What about all those tears and holes that we all know are in every Tyvek install??

We don’t let UV get through to our tape or sheathing. Flashing or furring strips are always blocking the UV.

I’m not sure I understand your flashing concerns. All windows and doors are flashed according to the drainage method which is the most durable and robust. They are flashed directly over either the ZIP or SIS systems? Again, a much more solid assembly than putting Tyvek into the mix…

15 lavardera May 5, 2010 at 11:10 am

I was misunderstanding that there would be no vapor barrier to the inside. I could see that working, but essentially that is a configuration for a souther cooling centric climate. While it would work fine within a range of temperatures if you have a cold spell outside of the design range and your dew point moves inside your exterior foam you will have a disaster on your hands. I’m not convinced this is good practice.

I’m not advocating for Tyvek either. It has all the faults you are suggesting.

Let me try to explain my flashing concern. Flashing is an easy concept. Upper layers lap over lower layers, so water continuously runs off and away from the interior.

When you install a window in a traditional wall design, the window’s mounting fin is attached to the outside of the sheathing, and is covered by “flashing” tape. This ostensibly seals the frame to the sheathing as much as anything can be sealed to conventional sheathing. You air barrier then is laid over this – so any water running down the air barrier is carried over the top of the tape, reaches the top of the window frame and is directed outside the wall, drips off or drys. In the case of Tyvek it receives its own tape over that, but this does little more than hold it in place till covered.

With your Zip system you don’t have that air barrier sheet lapping over the top of your tape. Any water running down that wall has to pass over the top edge of that tape, without getting behind the tape, for that tape to act as flashing. That means 1 the tape has to be installed perfectly and 2 the tape has to perform to spec for ever.

The one is a physical flash – one material laps over the other. The second is essentially a “seal”. I think experience shows that a physical flash will always out last a seal.

16 Chad Ludeman May 5, 2010 at 11:22 am

Understood. This mechanical technique could be uses with SIS –

17 lavardera May 5, 2010 at 11:26 am

Reviewing the Chicago cold – climate wall note that they are flashing the horizontal joints in the foam, not taping. Taping is listed with a range of other sealants for the vertical joints. They also show a sill pan flashing for window openings through the foam, but don’t make any recommendation on how to flash the window head. The best solution would be a flashing similar to what they show on the horizontal foam joints, but this does not work with American style windows with a nailing fin. Thats not to mention that fastening your windows through exterior foam without solid blocking is probably a bad idea to begin with.

The solution is there needs to be a horizontal joint in the foam just above the top of the nailing fin so that a through foam flashing can lap over the top of the fin.

18 lavardera May 5, 2010 at 11:31 am

The Louisville mixed humid climate detail – here the southern cooling centric wall detail is more appropriate.

Curiously here they show a window head detail, and they are recommending a flashing strip that is then covered at the top with sheating tape – where as the zip tape does both of these functions, and most window manufacturers recommended flashing tape does the same. AGAIN, this head detail would benefit from building paper lapping over that nail fin and flashing tape. Just saying.

19 lavardera May 5, 2010 at 11:36 am

Yes – that video showing the groove into the foam addresses the issue. Now even if the top of the tape is not perfect or opens up over time it will remain water tight.

Ok, now how do you handle this with the ZIP sheathing? You don’t want to groove the OSB because then water would soak into the underlying wood strands.

20 lavardera May 5, 2010 at 12:02 pm

Just watched the video about the Habitat for Humanity House. Note they have added jamb straps to mount their windows and are not fastening them through the foam. I think in this case the best practice would be to cut the nail flange off the top of the window and put a through foam flashing over the window head.

21 Dave May 5, 2010 at 5:03 pm

If anyone wants to see a really bad tyvek wrap job a few blocks from the Skinny, then check out the the house at York & Almond St. You can see the tape coming loose and plenty of holes in the wrap. Oddly enough there are a few portions of the house that have ZIP and the rest is OSB.

22 Micah May 6, 2010 at 3:06 pm

Our company has been using the Zip system on our projects for 3-4 years now and love the product as a air & weather barrier. It simply can’t be beat for the price (marginally more) especially on tall, urban projects like you are doing (we are too).

However, I share the concern of the interior wall condensation. I want to move that dew point out of the wall cavity. Thus, our company is moving to 1 1/2″ – 2″ foam boards (we are in Indianapolis) for all our sheathings. So, I don’t want to take anything away from ZIP walls, but having condensation inside my walls isn’t ideal. Especially when you build a really tight house. I’ll take the extra effort, required by foam, of furring strips & shear bracing at the corners & other areas (windows, doors, etc…). As of this year, our company will move to foam sheating on 80% of our jobs.

One other note about the SIS is that you need to review the nailing patterns on that product. They are crazy intensive. Thus, we always use 1/2″ plywood (not OSB) at these areas and then overlay with the foam to get to the total thickness (i.e. – 1/2″ ply + 1″ foam = 1 1/2″ total sheathing thickness.)

23 Chad May 8, 2010 at 7:24 am

Great comment Micah, thanks! It’s good to see builders out there using these systems as standard practice. BTW, you guys are building some nice looking projects there in Indiana.

24 T.C. May 20, 2010 at 5:05 pm

Hello Sorry late to the party… I am interested to see good vetting of these products. Although I take issue with a couple of the points, I largely have to say that comments are spot on. Lloyd’s comments on foams containing some nasty stuff is true, but forward thinking companies are working on their fire resistance with other chemicals, and foaming agents are changing over to friendlier (environmentally speaking) products. That is what manufacturers are telling me.
What I like about these products is that regularly executed jobsite practices result in a better outcome from a durability standpoint, period. SIS and ZIP install as any sheathing would, and then get taped off with their respective proprietary products. End result is a durable and fairly airtight exterior envelope that acts as one weather resistive barrier. For some finishes, such as stucco, a second barrier is required by code, and some may want one anyway, depending on exterior cladding choices, such as fibercement products when no rainscreen is present. Both of these products add a high measure of durability to the wall assembly at little additional cost, and some may argue that you can save money using them.
In the case of SIS the exterior insulation is a freebie, and will considerably improve wall cavity temps thus reducing likelihood of condensation in times of high winter delta T. The post that alluded to the fact that, in the case of SIS, it is not a nailbase is a good point. Some serious advance planning needs to go into trim and siding details, although we/ve had success incorporating 1″ sis with 1/2″ xps and osb in areas such as corners and windows to allow for nailing of wider trims and corners.
Here is where the point about detailing and water infiltration comes in; The flashing details for water and air infiltration must be well thought out prior to construction. The people who have posted obviously know this well. As far as window installation with these products used as the WRB, head flashings must be installed over the rainscreen or packer at the head of the window then taped off to the plane of the sheathing. side details would be similar, with sill detail best coming out to face of siding. In the case of a job like Postgreen’s, where a siding product may not be able to span the framing spacing (thus seemingly requiring a nailbase) why not install the furring strips horizontally as long as they allow vertical bulk moisture movement? In the case of a well constructed home with a rainscreen, limited space/ air movement is all that is needed to allow for the wall to break capillary action or bulk moisture escape. Metal furring is a super choice for that.
Environmental concerns are a legitimate argument for foam products, but in their defense, and in this case SIS, makes an extremely durable and well-performing wall assembly.
As a matter of clarification, Dow SIS is polyisocyanurate insulation with a facer to allow for tape adhesion. The structural backer is a product similar to masonite, or hardboard. The backer is 97% post-consumer wood fiber. The other 3% is binders. That makes Dow SIS 80% post consumer content by weight. So, at least there is some good bonded to the bad.

25 Lillian August 21, 2010 at 3:39 am

In process of building new home. Plan to use 1″ 4×8 sheets of rigid foam over 3/4″ OSB. We will install the foam so that the seams to not fall directly over OSB seams, making for a more “air-tight” application. DO NOT PLAN to use any tape because
1)expensive to purchase 2) labor cost to apply 3) most likely won’t stay in place very many years 4) when the brick-layer nails or screws in his brick-ties there would be many places the tape would be torn….and 5) most importantly….I feel I would be getting the house “too air-tight” and moisture could not escape

26 T.C. August 23, 2010 at 4:45 pm

Lillian- I am not sure I am the best berson to respond to your post, but I feel you should rethink your wall assembly. 3/4 OSB for a wall? I think you’ll find that 1: 3/4 is not needed for wall bracing 2: is an expensive way to gain a nailbase for your wall ties that can be fastened to studwork 3:is not durable in the face of moisture in your wall cavity, which you will get with the lack of control of air infiltration. Your comment on the tape is well taken, but consider this; eliminating mastic or tape on the foam means you’ll still need the code-required weather resistive barrier, which in the case of housewrap will add several times the cost of the tape in both materials and labor. Remember, both products that are mentioned here act as your weather resistive barrier when tape is used. Also, allowing the building to “breathe” will allow air to flow into and through your wall assembly in an uncontrolled manner. Allowing your conditioned indoor air to “dry” to the outside will, at its worst, cause uncomfortably low indoor RH in the winter, while causing severe moisture problems on a summer day with wind. Where goes air, so goes moisture. on a summer day with 100% RH, the air movement over the structure will cause negative pressurization inside the house, thus sucking air through your walls and moisture will come with it. A better approach may be to tighten up the envelope and condition your air properly. You also say you are going to use 1″ of foam; what is your climatic region? In the northeast that is likely not enough to negate the possibility of condensation within the wall cavity. When you look at the cost of your proposed wall assembly as opposed to a Zip/foam/tape assembly, I thik you’ll be pleasantly surprised to find that you can improve performance without sacrificing quality (quite the opposite) or your budget.

27 patrick October 27, 2010 at 8:56 pm

We’re looking into using the DOW SIS, but have a few questions.

1) When attaching SIS is it to be nailed to studs inside the permitter of the board? In either case don’t the nail (or staple) holes break the moisture barrier, or are all nail line to be taped as well?

2) the board cannot be used as a fastening substrate for siding, correct? That is, you cannot nail through SIS into the framing to attach siding, or you cannot nail into the SIS only to attach framing?

3) If furring strips are required to attach your siding to, then by what means are the furring strips themselves attached to to the sis?

4) can the board be applied and count for lateral bracing even if two or more pieces are connecting the top and bottom plate?

Thank you very much.

28 T.C. October 28, 2010 at 8:15 am

Patrick- I can field your questions. We have a wall panel manufacturing line where SIS has proven to be a real win. First, SIS is structural, but it is not a nailbase. So, to answer your questions in order:
1:Sis is to be nailed or stapled around the perimeter and “in the field” of the sheet. If it is part of the braced wall line as designed for your building, perimeter nails/staples must be 3″ on center and in the field, 6″ O.C. If it is not part of the braced wall line, 6″ on edges and 12″ in the field is sufficient. Wall bracing is an ever-increasingly difficult part of the residential code for a lay person to get their head around, but if you want to read up, it is sections 602.10-602.12 in IRC ’09. It is about 18 pages of stuff. As far as the nails or staples breaking the vapor/wrb, Dow tells us that the product is “self sealing” and that those penetrations do not weaken the product effectiveness when the fasteners are driven in properly. That being said, the only way to countersink the fasteners properly is to use pneumatic tools. Joints will be taped which will cover most of the fasteners anyway.
2: The product is not a nailbase, but you can fasten through SIS into the framing for anchorage of your cladding. Some thought may be needed at building corners.
3: Furring is not required, but a rainscreen detail may not be a bad idea, design-wise.
4: Sis is approved for wall bracing, but some limitations apply with the product, namely wall height. Read Dow’s literature on this carefully. Hope this helps.

29 Robert Riversong January 22, 2011 at 2:36 am

Lots of misinformation and misunderstandings here.

“I’m a bit confused as to which type of foam is no good.”

All petrochemical materials are damaging to the environment and to human health. Some are worse than others. All the plastic foams have extremely high embodied energy. XPS and urethane have very high global warming contributions. XPS and EPS have persistent bio-accumulative toxic brominated fire retardants. Some spray foams have forced occupants to vacate their homes because of persistent outgassing and chemical sensitivity.

“We don’t really think there is such a thing as the perfect green product.”

There is almost nothing as green as responsibly harvested wood products, with as little industrial manufacturing as possible. Sawn boards are much greener than plywood, which is greener (and more durable) than OSB.

There are lots of comparisons here to OSB, which is basically a junk building material. Comparing SIS or any other sheathing to OSB is like comparing an insulation to fiberglass (which is also a nearly worthless product).

“We use a rain screen detail on every home that requires furring strips to be fastened to studs that will then act as our nailing base. This is needed to matter what type of sheathing we use.”

No it is not. If the entire structural and thermal envelope can breathe in both directions and the cladding can as well and is not a reservoir material, then rainscreens are unnecessary except in the most severe rain/wind climates.

“We have seen countless studies that show that building wrap is pretty much worthless.”
“The Weathermate tape from DOW does a very convincing job of sealing all seams.”

Please link to a single one. If you mean they don’t function as air barriers, they are not intended to. They are WRBs, and WRBS must be shingle-lapped to function reliably. That means the best WRBs are made of strips of asphalt felt rather than 9′ wide sheets that require taping. Tape relies on a chemical bond and can not be considered a reliable long-term seal. Physics (gravity drainage) always trumps chemistry.

“Are there alternatives to rigid foam that may be better for the environment? Absolutely. These products also happen to cost much more and are not readily available.”
“show me the perfect wall for our climate and it will probably cost a fortune to build…”

What products are you referring to? With a deep wall cavity, insulated with moisture-buffering insulation (like cellulose) that can breathe in both directions, there is no need for exterior insulation of any kind. And double-wall or truss-wall systems are the least expensive method of creating a durable and highly-insulating envelope.

“The interior drywall layer is an air barrier only. It is NOT a Vapor Barrier.”

The interior surface, in a cold climate, is the appropriate location for the air barrier, since it’s purpose is to restrict the movement of INSIDE warm, humid air into the thermal envelope. The exterior requires only a WRB – able to resist rain and wind.

IRC § 322.1: Moisture Vapor Retarders/Moisture Control. In all framed walls, floors, roofs, and ceilings making up the building thermal envelope, a vapor retarder must be installed on the warm-in-winter side of the insulation, unless the framed area is ventilated to allow moisture to escape. (Vapor retarders are designed to prevent the movement of moisture-laden air from the warm side of the wall to the cool side. In temperate climates, vapor retarders are placed on the interior (warm in winter) side of the wall cavity; in hot, humid climates, they are placed on the exterior (warm) side of the wall cavity. According to the Asthma Regional Coordinating Council of New England, walls should be designed to dry to both the interior and the exterior and basements should be designed to dry to the interior.

lavardera: “That wall system is intolerant of any failure and is a recipe for mold, and eventually rot.”

Lavadera is absolutely correct. A cold-climate wall system must be able to resist the exfiltration of conditioned air, slow vapor diffusion from the inside, and be able to dry in both directions but predominantly outward.

Anything that restricts the outward drying of the structural envelope has a high probability of reducing the long-term durability of the structure. And if that exterior restrictive layer also raises the average temperature of the sheathing or framing, then it increases the probability of the growth of mold or decay organisms. It is a myth that hygroscopic sheathing is protected from moisture if it remains above the dewpoint. Wood materials are susceptible to mold at relative humidities of about 80% and to decay at about 90%. If they are kept warm, then biological activity will be accelerated.

30 T. C. January 24, 2011 at 11:29 am

Mr Riversong- I am a fan of many techniques that you champion, but I am confused by some of your points here. It seems that you are saying that a wall you may build would have solid sawn sheathing, presumably green lumber to reduce the amount of embodied energy in the product. I further assume you are then installing a WRB over this sheathing, then attaching a wood(?) siding directly over that with no rainscreen? You use cellulose insulation also. This system may be forgiving in its ability to absorb and give back moisture; and that is a good thing. But what about baint finishes on the exterior? I think that is an apples and oranges difference from what Postgreen is doing; focusing much more heavily on air sealing and using low perm sheathings and rainscreens behind exterior claddings (fiber cement) where moisture levels could be significant in their mixed humid climate.

The tape that Zip (Huber) uses is butyl. It is well performing, but your point about preferring a mechanical joint over a chemical bond is well taken.

Dow’s SIS is not hygroscopic. The interior face has a melamine facer over a wood composite structural component, then that assembly is bonded to a polyisocyancurate (closed cell).

Postgreen uses cellulose in the wall cavity. As you know, this material is very effective at absorbing, disbursing, and giving back moisture (and here we are talking about vapor) that may enter.

You reference R322.1 above for WRB requirements. That section in 2009 is the “flood resistant construction” section. in IRC ’03 and ’06 it was “accessibility”.

Vapor retarders are addressed in R601.3 in the ’09 IRC. I think the verbiage you reference is older than IRC (BOCA?), and many building scientists and concientious builders may now take issue with any suggestion that a wall cavity should be “vented”. I remember those days, and I am happy to say I no longer see people drilling 1″ holes in their top and bottom plates when using vapor barriers or exterior rigid foam.

I do agree that walls should be able to dry effectively, but in a mixed humid climate, effective air sealing and agressive attention to detail, coupled with an HVAC system capable of addressing humidity levels seems a great solution.

My questions are these; 1: what type of cladding do you use that in not a “reservoir material” for those looking to avoid vinyl? and 2: Do you disagree with those that favor an airtight approach to their wall/roof assemblies? Those systems require very low/no permeability, no? 3: OSB as a “Junk” material. From an embodied energy standpoint? From a durability standpoint? From a structural standpoint? I fail to see how you make that distinction. Sure, there are poor performers in the commodity OSB world, but that does not mean the technology is not sound. What if one was to use solid sawn balsa as sheathing? OSB uses low economic value, young trees for fiber source. Ply and your solid sawn products use much older and higher value (both economically and ecologically) trees large enough to produce wide boards or veneers. Those trees are better left standing, or cut for dimensional lumber. Is it phenolic resins that you do not like? Great discussion all. Thanks.

31 Robert Riversong January 24, 2011 at 2:01 pm


It seems you’re confusing a ventilated envelope with a breatheable envelope. In the building science community, a “breathing” envelope or material is universally understood to be one that is permeable to water vapor, and as such facilitates drying.

No one is talking about a leaky envelope, but three things are necessary to avoid moisture problems: 1) keeping moisture out of the envelope (by moisture control, air barriers and vapor retarders); 3) allowing the envelope to dry by vapor permeance; and 3) using materials that can safely store moisture between wetting and drying cycles. All building envelopes need to be relatively air-tight – the only argument is how tight is tight enough.

Air-tight assemblies don’t require “very low/no permeability” – on the contrary, every envelope must be vapor open in at least one direction. In cold climates, it’s far better to be vapor open in both directions. In humid climates, it’s best to be vapor open only on the inside. The more we reduce air and heat flux through an envelope, the more important vapor permeance becomes as the only remaining drying process.

Yes, SIS is not hygroscopic. And it’s also an exterior vapor barrier, which is foolish in a cold climate.

Reservoir claddings are such as brick and stucco which can hold large volumes of water, which can be driven by solar radiant pressure into the envelope. Wood siding finished on all six sides with latex solid-color stain resists water absorption but allows vapor permeance (and protects the wood from UV). Attached to a WRB-protected breatheable sheathing with hygroscopic insulation behind it, and good roof overhangs for shielding, there is no need for a rainscreen. A rainscreen becomes necessary with exterior non-breathing foam and claddings (like fiber-cement) that are absorptive and dimensionally unstable.

OSB, originally created to use waste wood and fast-growing trees, has increased so much in demand (because it’s cheap) that whole-tree harvesting is now used as a feedstock. As per Dr. Joe, the more we process wood the less durable it becomes. Sawn lumber worked well for centuries (and still does); plywood is more vulnerable to moisture and delamination and somewhat less vapor permeable; OSB has more formaldehyde resins, is less permeable and is more vulnerable to mold and decay (in addition to permanent edge swelling and reduction in nail holding strength). OSB can be more highly processed (more embodied energy and artificial additives) into more durable varieties (Advantech, Zip, etc), but more processing does not necessarily make them durable over the life of a house and exacerbates moisture problems because they are even less permeable.

32 patrick January 24, 2011 at 8:10 pm

How is it that something can be vapor permeable while also being air tight? Vapor is after all a gas, i.e. air.

33 Robert Riversong January 24, 2011 at 8:56 pm

Have you ever worn a Goretex jacket? It keeps wind and rain out but lets the water vapor from insensible perspiration through to keep you dry.

That’s how all housewraps work, too.

The other major constituents of air – N2, O2, CO2 – are all larger molecules than H2O, and water has almost magical properties compared to any other terrestrial substance.

Water is the third most common molecule in the Universe (after H2 and CO) and the most common compound, the most abundant solid material in the universe (99 percent of all water is ice) and fundamental to star formation. Water is the most abundant substance on earth and the only naturally occurring inorganic liquid. Life cannot evolve or continue without liquid water, as it is essential for metabolism, photosynthesis and the thermoregulation of our bodies & the earth.

It is the most common but least studied substance on earth and no single scientific model is able to explain all of its properties. (Science fiction writer Harlan Ellison once said that the most common elements in the universe are hydrogen and stupidity.)

- water is the only terrestrial substance that naturally exists in three distinct states
- water has an abnormally high melting point, creating the abundance of liquid water
- water has the highest specific heat of all liquids except ammonia
- water has the highest heat of vaporization of any molecular liquid
- water has the highest thermal conductivity of any liquid (except for liquid metals)
- water has exceptionally high surface tension
- water is the universal solvent
- hot water freezes faster than cold water
- solid water (ice) is less dense than liquid water and hence floats
- boiling water will turn instantly to snow at temperatures below -25°
- water has at least 5 liquid phases and 14 solid phases (remember Ice 9?)
- when supercooled will turn instantly to ice when disturbed
- when superheated will turn instantly to vapor when disturbed
- at -184° F water turns super-viscous like molasses
- at -211° F water turns amorphous like glass
- at the moment of germination, the water in a seed can exert nearly 6,000 psi
- homeopathy is correct that water has a “memory” of what was once dissolved
- there is evidence that it also retains thoughts, moods & conscious intentions

34 T. C. January 25, 2011 at 10:29 am

@ Robert Riversong: I was not confused about the difference of ventilation and vapor migration; I was responding directly to the quoted code language you posted:

” a vapor retarder must be installed on the warm-in-winter side of the insulation, unless the framed area is ventilated to allow moisture to escape.”

As I said before; sadly, science is only now catching up to the multiple variables at play within a wall or roof cavity. “Ventilation/breathability” was achieved in numerous ways in the not so distant past. Some were bad. Some old houses performed admirably, from a durability standpoint, just due to the huge amount of air passing through and drying the walls and cladding. However, I take issue with you on the fact that your wall system, as described, facing say, west, would fare particularly well in a long term durability test. Specifically, I believe your cladding might be all but rotten in 20 years. Yes, I’ve seen 100 year old homes with wood siding that have had cellulose blown in the wall cavity and the cladding is holding up well, but that is not today’s construction or materials.

Your comment:”No one is talking about a leaky envelope, but three things are necessary to avoid moisture problems: 1) keeping moisture out of the envelope (by moisture control, air barriers and vapor retarders); 3) allowing the envelope to dry by vapor permeance; and 3) using materials that can safely store moisture between wetting and drying cycles. All building envelopes need to be relatively air-tight – the only argument is how tight is tight enough.”
I agree wholeheartedly, but I see no danger in very tight construction; do you? vapor permeance is a separate issue. I also agree that exterior rigid foam, poorly applied, with a lot of air/thermal bypasses in the cavity might create a very bad situation in a cold climate, but, getting back to the specifics of this original post: In a very tight wall, with significant levels of exterior rigid insulation, cellulose in the double-stud wall cavity, and a well controlled indoor air environment, what is the risk of moisture in the wall cavity? If the ONLY source of moisture in that assembly comes from vapor migration, I’m thinking the risk (moisture buildup/poor durability) is pretty low.

As far as OSB, yes, we will agree to disagree. It is not as strong in some directions as a plywood product, but does it need to be for homebuilding? I do not think so. I agree that whole tree harvesting takes place for OSB production, but that tree does not need to be as old, as straight, as narrow a species requirement, or as large as a tree needed for solid-sawn boards & timber or veneer stock (ply). It is a good use of what would be a waste product. It crossed my mind, but I do not believe you were trying to make the case that trees that could otherwise be used for boards or veneer are nefariously being chopped for osb; that makes no logical or economical sense. OSB is not as close to a natural building material as solid sawn lumber; agreed. Some OSB technology undergoes added processing, adding to its embodied energy penalty, but also extending service life through much improved strength/durability. That extra embodied energy (a small percentage of the product total), in my opinion, will be offset quickly by that extended life cycle. Let’s face it; the worst offenders, product-wise, in terms of embodied energy are those that must be replaced prematurely.

Natural building proponents come at this one way, builders who embrace highly engineered materials come at it from another angle. In the end, the initial embodied energy of the structure, cost to operate (BTU/SF), building life span (durability/req’d maintenance), and disposal costs (environmentally speaking) are the litmus test for all buildings. It would seem there are strong arguments to be made both ways.

35 Robert Riversong January 25, 2011 at 3:32 pm

“sadly, science is only now catching up to the multiple variables at play within a wall or roof cavity.”

What I find sad is that science is only now catching up to the timeless wisdom which guided humanity for tens or thousands if not millions of years living in harmony with our environment.

For instance, rainscreen technology was used hundreds of years ago on Norwegian barns. Common sense. Now we need science or some “expert” to tell us what we should already know.

“I take issue with you on the fact that your wall system, as described, facing say, west, would fare particularly well in a long term durability test. Specifically, I believe your cladding might be all but rotten in 20 years.”

You “take issue” on what basis? On historical evidence? On your interpretation of building science?

Cellulose is the oldest building insulation material. Many types of cellulosic materials have been used, including newspaper, cardboard, cotton, straw, sawdust, hemp and corncob. Monticello was insulated with a form of cellulose. Modern cellulose insulation, made with recycled newspaper using grinding and dust removing machines and adding a fire retardant, began in the 1950s and came into general use in the US during the 1970s.

Modern cellulose insulation has a long and reliable track record and there is nothing in hygrothermal science which suggests it would not be reliable in the building envelopes I have designed and built for more than 20 years with no evidence of failure, and I teach hygro-thermal engineering.

“I see no danger in very tight construction; do you? vapor permeance is a separate issue…In a very tight wall, with significant levels of exterior rigid insulation, cellulose in the double-stud wall cavity, and a well controlled indoor air environment, what is the risk of moisture in the wall cavity? If the ONLY source of moisture in that assembly comes from vapor migration, I’m thinking the risk (moisture buildup/poor durability) is pretty low.”

Yes, I do. Cellulose, in particular, performs best in a thermal envelope that can breathe in both directions. At least one cellulose insulation manufacturer won’t honor their warranty if it’s installed with a vapor barrier.

When considering risk, a frequency/consequence matrix needs to be evaluated. Generally, low frequency/low consequence events can be ignored. High frequency events, with either low or high consequence must be planned for and mitigated, such as rainstorms and localized indoor relative humidity (showers or cooking, e.g.). But for a structure or system to be truly durable over the long term, low frequency/high consequence event must be accounted for in the design and enough resilience built in to prevent failure.

The “warm sheathing” approach, which also typically relies on the exterior foam board as the air barrier as well (and which Dr. Joe calls the “perfect wall”) relies on long-term perfection for the life of the structure. An intelligent designer, however, doesn’t assume that perfection can be attained at initial construction or maintained through the life of a house. There are two studies I’m aware of – one on cathedralized roofs and the other on walls – which deliberately introduced a normal leak event to test for effects. In both studies, roofs and walls that could not breathe not only would take months or years to dry but would also be maintained at sufficiently warm temperatures to encourage the growth of mold and decay organisms.

This is known as the “unintended consequences” of design. If one studies the history of modern scientific engineering, one will notice that virtually all engineered “solutions” entail unintended consequences that weren’t anticipated in the design process. The more complex or sophisticated the “solution” the more likely or more numerous the unintended consequences.

As you noted, old buildings often lasted hundreds of years because they did not resist the natural flows of heat and moisture. Trying to completely block these natural forces is as foolish as assuming that damming up a river will prevent flooding. All it does is make the rare floods far more catastrophic. You can’t fool Mother Nature. So the best building designs are those that work with rather than fight nature’s forces and flows.

“the worst offenders, product-wise, in terms of embodied energy are those that must be replaced prematurely.”

A better definition of durability is a material that outlasts its impacts on the earth. The greenest homes were the indigenous shelters of every earthly culture. Since their creation had very little impact on the environment, if they had to be repaired or replaced every few years they survived longer than the earth required to recover from their impacts. So, the more engineered, manufactured and energy-embodied become our building materials, methods and systems, the longer they must survive in order to outlive their deleterious effects on the environment. Simple and natural is always more green – and, in fact, more durable – than anything manufactured.

“Natural building proponents come at this one way, builders who embrace highly engineered materials come at it from another angle. In the end, the initial embodied energy of the structure, cost to operate (BTU/SF), building life span (durability/req’d maintenance), and disposal costs (environmentally speaking) are the litmus test for all buildings. It would seem there are strong arguments to be made both ways.”

I would say that the litmus test is the impact, positive or negative, that any structure has on its environment, on the health of its occupants, and on the relationships that create community. This, by the way, is the litmus test that the Amish have successfully used for centuries and that Wendell Berry developed for himself decades ago for choosing appropriate technologies.

36 T. C. January 26, 2011 at 9:34 am

Robert, We are getting closer to agreement! I would love to further discuss this and your insights, but I feel we have hijacked this thread. My e-mail is T.C.

37 T. C. January 26, 2011 at 4:16 pm
38 Robert Riversong January 26, 2011 at 8:34 pm

Note from Martin Holladay’s GBA blog on WRBs that the IRC still specifies #15 felt as the prescribed code-acceptable weather barrier – all substitutes must at least meet the specifications of this tried-and-true material.

Note also that there are questions among the most prominent building scientists about the long-term reliability of ZIP Wall with taped (and non-warrantied) seams as a WRB (even though Huber managed to get an IRC approval).

One of the primary benefits of 3′ wide strips of shingle-lapped felt WRB that is not noted in the article is that it’s much easier to integrate with window and door flashings (as in AAMA flanged window installation methods A and B), without relying on a taped flap over the top window flange. Physics (gravity drainage) always trumps chemistry (tape adhesives) for reliability.

39 patrick January 27, 2011 at 10:38 pm

Saying that house wraps work like gortex doesn’t really say how house wraps work. You said a lot about water, mostly all very interesting. But not a lot about vapor permeable layers. Is the explanation merely that since H20 is a smaller molecule than many of the other constituent molecules of the atmosphere it passes through the vapor permeable layer while the rest of the “air” does not? Also, it isn’t true tout court that warmer water freezes faster than cooler water, but merely that it can.

40 Robert Riversong January 28, 2011 at 12:15 am

The explanation is partly about molecule size, but also likely has to do with the electrically dipole nature of the water molecule and its high hydrogen bonding potential.

But a mechanism for motion requires a driving force, which in the case of vapor diffusion is vapor pressure (partial pressure of a mixture of gases). Since the relative concentration of the other molecular constituents of air are approximately the same on both sides of a membrane, there is no partial pressure differential (only air pressure differences). But absolute humidity differentials create considerable persistent vapor pressure differentials on the order of 1,000 to 2,000 pascals. In comparison, a 20 mph wind exerts 50 pascals and a 40 mph wind exerts 200 pascals.

The simple fact, however, is that many materials are air barriers but permeable to water vapor.

41 Chad Ludeman January 28, 2011 at 7:34 am

I’m jumping in here to stop this comment thread from getting off track. I’ve already had to delete and edit some rude and inappropriate comments made on this thread in the past week that we do not tolerate here.

Discussions are encouraged, but insulting other readers and those taking the time to keep this blog up and running will not be tolerated. You can start your own blog or website if you want to write pages and pages about how your way to build homes is better than everyone elses…

I’ll also add one last comment that the one of the purposes of this blog is to make an attempt at influencing the building industry in the US to adopt higher quality building practices. It’s great is the small builders and builder/owners are building fantastically energy efficient and durable assemblies, but if we can all influence any of the top 10 builders in the US to insulate better, install a proper WRB, seal up obvious gaps or install a rainscreen then that impact on the environment and the building trends in the US will be far greater than any of us small guys can do on their own.

Nobody is going to convince the big builders to drop their construction practices and adopt complex truss systems named after themselves and use locally rough sawn lumber in the thousands of homes they are building every year…

Comments are now closed on this post until further notice.

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