Earlier this week we posted on cutting labor costs associated with Cellulose insulation installs. It occured to me in some of the comments that we have never posted on our “magical” electrical strategy to help improve the insulation and air tightness of our homes. The truth of the matter is that we actually don’t use any magic (especially the kind shown on the right). Simply a bit of common sense and a sleek wireless lighting system. I will explain.

A bit of background on how this originated

After the 100K project, we started to really focus on how to improve air tightness and insulation values in our walls. We weren’t sure if we would keep using SIPs which can making running electric difficult.  We also weren’t sure if we wanted an interior or exterior air barrier, or even both. This got us thinking a lot about those wires, light switches and outlets in our walls that were taking up valuable insulation space in our exterior walls and also creating weak spots in our air tight drywall layer.

One of the most valuable things I learned while teaching myself Manufacturing Engineering in college (please don’t stick to only the books your profs recommend for you kids) while going for my Industrial Management degree was that “the best way to improve a slow or error ridden process or component was to eliminate it.” This jewel of knowledge came to me one day. All we need to do is eliminate those pesky wall outlets and light switches to improve the efficiency of our wall assemblies! OK, now how do we do this affordably?

Eliminating outlets in your walls

Let’s start with the easier of the two, eliminating outlets. This was relatively easy once we thought about it. Simply take your wall outlets and move them to the floors. Simple. Easy. Done. Yes, this costs a bit more in floor outlet material and labor, but you only need to do it on exterior walls. This keeps the additional cost very low, especially in row homes with only two very short exposed walls. Here’s a shot of one of ours in the recent Skinny Project below.

Eliminating light switches in your walls

This guy didn’t come to us as quickly. Luckily we remembered one decent product from Green in Boston a few years ago. That valuable trip was sponsored by Bolt Bus, Nic’s Aunt in the Boston burbs and our ability to stretch two, one-day floor passes into full 3-day passes. The product I am referring to is the Verve Living System for wireless control of residential lighting.

There are many expensive and complex commercial wireless lighting systems out there, but the bright people at Verve have packaged some of that same technology into an economical residential package with just the right amount of functionality. The basic system incorporates a fancy 10-channel controller where you can wire up to 10 lighting circuits (it can also do ceiling fans, outlets and now wireless thermostats). Once the lights are wired to the controller, they can be easily programmed to be controlled by one of Verve’s wireless switches which can simply be adhered or screwed to any location in your home. The switches are powered by the motion of clicking them so there are no batteries to replace ever. All wiring from switches to the actual lights are eliminated, so the labor savings in installation account for the extra cost in materials from Verve for the most part. Our electricians actually love the system due to reduced time of install and we love it because it eliminates all wires and leaky switch boxes in our exterior walls. We’ve found that our clients also love it as they can rearrange where the switches are located, how they are programmed and even buy more if they want.

That’s it. After searching the Verve site for this post, I found a few new products we have been waiting for from them, so hopefully we’ll have a new post in the near future on added functionality and uses for their system.

As you may well know, we are big fans of cellulose insulation. The Skinny project was the first time we used cellulose and we learned some valuable lessons that we plan to apply to future projects like Avant Garage that Nic has been telling you about lately. As always, we are attempting to continually improve the quality, efficiency and cost of construction. That’s a big part of what this blog is about after all.

We learned two major things while trying to stuff 9.5″ of cellulose insulation into the walls of the Skinny Project.

1. 10′ tall x 10″ thick of cellulose is very heavy and wants to make your drywall pop off the studs.
2. The majority of the labor installing the cellulose insulation was actually in netting the stud walls prior to blowing it in the cavities.

Let’s dig a bit deeper into these two observations.

The first point is illustrated in the picture below. You can see that the cellulose is bulging the netting out and that the netting is stapled to the face of the studs. This invokes nightmares for the drywall crew. For starters, the crew has to throw their bodies against the drywall in order to press the cellulose back in allowing them to fasten the sheets to the studs. Secondly, due to the netting running over the studs, they can not glue the drywall to the studs to help prevent nail popping. The end result is that it takes longer for the drywall to be installed and we get more nail pops than normal that need to be fixed for the clients once they move in. Neither issue is a huge deal, but still an opportunity for improvement.

The second issue relates directly to the installed cost of cellulose insulation. We did some research and found that the cellulose product itself accounted for about 1/5 of the total install cost we paid to our insulation contractor. The rest is labor and staples for the most part. As stated above, over half of the labor was spent simply installing the netting before a single scrap of cellulose was blown into our walls. You can see how many staples it takes to hold in the netting in the picture above to get an idea of why this takes so long.

Enough talk. On to our hopeful solution to both of these issues. Install the drywall prior to blowing in cellulose into the walls. Simple right?

This came to us when discussing new ideas with the Hybrid Construction crew for improving the air tightness of our envelopes. Installing the drywall first allows the hanging crews to easily glue all sheets to the studs with no hindrances. It also eliminates the need to press in the cellulose to get the sheets to lay flat because there is no cellulose. Once this is done, the insulation crew can come through and simple drill holes for their cellulose pumps just like they do for retrofit walls. They will do this in between hanging and mudding the drywall so there is no extra charge from the drywall crew to spackle over these holes.

We have since verified the effectiveness of this technique with a few other super insulating freak contractors across the country. If our calculations are correct, we should not only save time and improve quality, but we should be able to chop our cellulose insulation costs in half! Not bad.

Anyone out there trying something similar? Share it with us in those comments.

In my last post about super-insulated wall assemblies, I referenced a future post about the superiority of Dense-pack Blown-in Cellulose insulation over other insulating products. Well, this is that post. We’ve talked about insulation in the past, but after extensive research and pitches from other insulation fanatics we’d like to put Cellulose in the spotlight as what we consider to be the best insulation product on the market today.

Why is Blown-In Cellulose so awesome in bullet point format:

• Inexpensive – It’s not as cheap as Fiberglass, but it’s much more reasonable than rigid and spray foam options.
• Lowest Embodied Energy – Of all the types of insulation, cellulose takes the least energy to produce. It is recycled newspaper after all and often it is locally sourced and manufactured.
• Fills all gaps – While batts will leave many gaps around electrical wires and boxes and will not always hug the studs, blown-in cellulose fills every available gap when installed properly.
• Air Retarder - Air leaks in your homes walls and roof can cause significant losses in efficiency. Cellulose significantly resists the flow of air through your walls and maintains it’s rated R-value even in heavy gusts. This feature also makes cellulose a great fire retardant compared to batts.
• Maintains R value – We hinted at this in the last point, but cellulose is exceptional at maintaining its advertised R value. Fiberglass wilts in the face of wind and extreme temperature difference between inside and outside.
• High thermal mass – It’s not called dense-pack for no reason. Cellulose adds thermal mass to your walls that has been proven to help a home maintain its temperature (pdf) for days longer than a similar home insulated to the same R-values with fiberglass.

These are the reasons we have come to love cellulose. It’s not just us though. Search around. More and more super-insulated and Passive Houses are switching to cellulose all over the world.

For a more detailed comparison of insulation products, check out this table at cellulose.org. Did we miss anything? Let us know in the comments.

You know by now that we’re all about finding the best bang for our buck when it comes to energy efficient construction. That’s how this whole thing started. It’s been a while since we’ve posted on advancements in our building philosophy, so why not talk about our next super-insulated wall assembly that we think could just possibly be the most affordable wall assembly that achieves maximum R-value and minimum thermal bridging with the least impact on your budget.

This is a bold statement, so I expect some comments and rebuttals. Here is my rationale.

THE Wall Assembly

• Double stud wall, 2×4′s on 24″ centers.
• Dense-packed cellulose in the wall cavity.
• OSB exterior sheathing.
• R-10 continuous exterior insulation, taped at all seams.

Here’s why this wall assembly is chalk full of awesomeness:

• Double stud walls on 24″ centers is the easiest and cheapest built thick wall cavity. Both material costs and labor costs are extremely low compared to alternatives (TJI’s for instance).
• Cellulose is economical while also being the best green insulation product known to man (see future post on cellulose superiority). It’s cheap. It barely has a carbon footprint. It fills all voids. It retards air flow like a champ. It has high thermal mass compared to alternatives like foam and fiberglass. Did I mention it’s affordable? This is important.
• OSB is cheap and makes it easier to attach cladding and laterally brace your structure.
• Continuous exterior insulation is the icing on the cake. It’s not uber cheap or low in the carbon footprint category, but used sparingly, it can be quite effective. It eliminates any thermal bridging worries that might have you up at night. When taped, it also can virtually eliminate air penetration and double as a water resistive barrier allowing one product to serve three important roles.

The next Postgreen Home, the 2 point 5 beta, will incorporate a 9″ thick double stud wall filled with dense packed cellulose (R-30) and sheathed in OSB and capped off with 1.55″ (R-10) of exterior Poly-iso rigid insulation. This will result in a wall with an R value of 40 and absolutely no thermal bridging. This will be our best wall assembly to date and most likely the wall we will stick with going forward. [Please forgive discrepancies from this description and the image above]

Inferior Alternatives?

One of my hopes in posting this hypothesis is that one of you guys out there will prove us wrong and give us a better wall assembly that packs more bang for the buck. Here are some of the other options I will shoot down in advance:

1. Excessive exterior insulation – As we stated above, rigid insulation is not cheap and has a larger carbon footprint than many other insulations. Therefore it should be used as sparingly as possible. R-10 is the minimum amount needed in most US climates to mitigate dew point issues that could cause moisture in your walls. Lastly, going over 2″ in thickness in exterior insulation will drive up the cost of your fasteners and labor required to attach your exterior cladding to your framing underneath.
2. Spray foam – While spray foam could be argued to be one of the more effective insulation options out there, it’s by far the most expensive and one of the most damaging to the environment with it’s ozone killing component and high carbon footprint.
3. Any type of batt insulation – Seriously?
4. ICF’s - Expensive, built of harmful foam, hard to get a high r-value and filled with concrete.
5. Big ass SIPs – These have the same problems as excessive amounts of foam as that is what the core is comprised of. Also, have you ever tried to lift a 10″ – 12″ roof SIP into place as a wall? They’re really heavy and unwieldy, adding to your install costs.
6. Blown-in Fiberglass – Substituting fiberglass for cellulose would decrease your costs slightly while achieving the same R-value. The big downsides are that it has a much higher carbon footprint, virtually no thermal mass and does not resist airflow, crippling it’s advertised R-value in the face of any air movement through your walls.

Let the comments roll.

It occurred to me that we haven’t really written a good post dedicated to vented rain screen assemblies. A rain screen is basically a gap created in between the sheathing of a house and the exterior cladding. It is considered by most building experts to be the most durable method of building an exterior wall and almost all commercial cladding details implement some type of a rainscreen. We have decided to use a vented rain screen on all of our Postgreen Homes and will talk about what we have learned to date in more detail below.

Benefits of a Vented Rain Screen

There are a couple of key benefits to using a vented rain screen assembly on any building that improve the performance and durability over the life of that building. Let’s put them in list form.

1. Equalized pressure means less air infiltration inside your building. Since there is an air gap between the exterior sheathing and cladding, the pressure is equalized with the exterior atmosphere. I’m no scientist, but basically this means that air is not going to be fighting hard to enter your building when it hits the cladding because the rain screen has eliminated the large pressure difference that usually exists between the exterior and interior of the home and various layers in between. This helps when you are trying to build homes as air tight as we are in order to achieve maximum energy efficiency.
2. Water the makes it past the cladding will drain and dry out, keeping the guts of your walls dry. This is where the durability claims come from. Water will eventually make it through any and all cladding assemblies on a building. The vented rain screen makes sure that when water does get through it is able to drain down the face of the Water Resistive Barrier and out the bottom or simply dry out on its own due to the air gap behind the cladding. This not only helps to keep moisture from getting into your walls assembly (which is bad), but it prolongs the life of whatever cladding is used by allowing it to dry out when wet from both sides.
3. An extra layer of air keeps your building cooler. In most homes, the sun hits your cladding which is in direct contact with the sheathing. The heat from the sun is transferred directly from the cladding into your walls. This makes your building warmer than necessary. The air gap created by a rain screen keeps the face of your sheathing much cooler. This is more important in the South where cooling loads dominate heating loads, but it’s still a nice feature in the north.

How to Build a Vented Rain Screen

There are many other people on the interwebs that I have linked to below that have described the how-to’s of rain screen building, so I’ll keep this brief. Here are the basic elements of any vented rain screen assembly:

1. Furring strips or a Drainage mat to create the air gap in between your sheathing/WRB and your exterior cladding. We list options for this material below, including our new favorite, The Furring Master!



2. An insect barrier at the bottom of the rain screen assembly gap with proper mechanical flashing. You want to keep the bugs from nesting in your rain screen from the bottom and water from draining into your basement.



3. A path for air to flow at the top of your cladding assembly. If you seal the top of your cladding to your roof cap or top trim piece, the rain screen is compromised by insufficient air flow from top to bottom.



4. A bit of extra care and planning at all window and door openings in terms of proper flashing. A good designer or flashing expert can help out here, but there are many details online for this as well that are simple to follow if planned for.

Material options for implementing Vented Rain Screens

There are many simple material options for creating the vital gap needed to build a vented rain screen system in residential buildings. There are much fancier systems implemented in commercial construction that we are no going to get into here. Some of the choices and their pros and cons are listed below:

• Pressure treated lumber – This option is one of the most popular as it is a familiar material, readily available and not too expensive. Rips of pressure treated plywood can be used or 1x material. This is what we used on the Passive Project. The main drawbacks are that the wood is not consistently flat and straight for precise cladding applications and water can be trapped between the wooden strips and the WRB with no room for venting where all strips are located.
• Mesh ventilation product – There are many mesh products available that are thin and easily applied in roll form over your WRB with a slap stapler. These products work great and eliminate the problem of trapped moisture completely that occurs with wooden furring strips. The main cons are the price and the uneven compression that can result in wavy cladding when fasteners are attached with different pressures. This is the product we used on the 100K House.
• Metal furring strips (The Furring Master) – Metal furring strips are our current favorite option due to a number of factors. The price is much better than the mesh products and not that higher than wood, depending on what type of wood strip you are using. They are perfectly straight and rigid which lends itself to the best finished installation of siding. One of our favorite aspects of it is that it has a hollow channel behind it that allows water and air to flow behind the surface, unlike wood. Lastly, it’s made of galvanized 22 gauge steel that is recyclable and can be left exposed in certain joints if desired without concern for UV degradation, decay or rusting.



Above is a picture of our installed Furring Master strips. We have studs at 24″ on center on the Skinny Project, but we installed the furring strips at 12″ centers. The strips in the middle that are not connected to studs are basically just maintaining the spacing from the wall and keeping the somewhat fragile panels rigid and secure.

• Miscellaneous other products – Although less common, we’ve seen others use creative products like corrugated plastic, rigid insulation and fiber cement strips.

Better links to Vented Rain Screen Instructions

Best post on Rainscreens ever by the BUILDblog – Fantastic diagrams and pictures from guys who really know what they are doing.

Green Home Building’s take on Rain Screens (PDF) – Good info, details and lots of hose wrap bashing. What more could you ask for?

Rain Control in Buildings by Building Science Corp – All sorts of good info about how rain and wind are trying to destroy your building and how to prevent them from succeeding.

]]> http://www.100khouse.com/2010/05/14/the-vented-rain-screen-via-furring-master/feed/ 22 http://www.100khouse.com/2010/05/03/zip-sis-multi-functional-sheathing/ http://www.100khouse.com/2010/05/03/zip-sis-multi-functional-sheathing/#comments Mon, 03 May 2010 19:48:17 +0000 Chad Ludeman http://www.100khouse.com/?p=1820

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.

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

Conclusions

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.

As we build the Skinny Project, we are taking care with all of our air sealing details and making notes on possible changes to reduce labor and complexity in all future homes. One of the key notes I picked up at last year’s Passive House Conference was that those who had been actually building these homes for a number of years were all stressing multiple layers of defense against pesky air infiltration. I thought I’d throw out a quick post to give the basics of our current multi-layer approach at sealing the movement of that crafty air thing that is so prevalent on our planet from sucking the heat out of or into our homes:

1. ZIP System sheathing with all seams taped with butyl tape.
2. Combination of gaskets and sealant sealing all critical rough framing connections.
3. Dense Packed cellulose insulation.
4. Drywall gaskets or continuous sealant along all corners, top/bottom plates and window/door openings.
5. Locate outlets in the floors and use wireless light switches to eliminate all drywall penetrations in the walls.

More details and diagrams to come as we improve our construction docs for Awesome Town.

In our first few projects at Postgreen, we used EPS SIPs (Structurally Insulated Panels) for our exterior walls and roofs which were very popular with the kids. We have decided to move away from SIPs in the Skinny Project in favor of using Advanced Framing Techniques and a Double Stud Wall design. Many of you have been waiting for an explanation as to why we’ve made this change, so let’s dive into it.

Why do we SIP no more?

First of all, we really have nothing against SIPs in general. We believe they are a great “hybrid prefab” type of product (along with ICF’s) and similar panelized systems. The main reasons we are moving away from SIPs are due to the challenges of our tight infill lots in Philadelphia. Many times the lot lines do not line up as drawn, foundations are out of level and neighboring homes are out of plumb. Since we are sharing party walls in every home, we have no room for error. The panels are ordered well ahead of time and they come perfect with little room for error. In the first two projects there were enough site modifications of the SIPs needed to negate the time and labor savings most SIPs projects are able to capitalize on.

If we were building detached homes, I’m fairly confident we would still be using SIPs as they offer a very tight and well insulated home with virtually no thermal bridging. As we get into larger projects, we may revisit the technology, but for now we are moving on to more traditional framing with some tweaks.

Double Stud Walls

First of all, we are using a double stud wall design on all of our front and rear facades. We are using a simple design that includes two 2×4″ walls on 24″ centers with a 2″ gap between the two walls. The studs are not staggered, but aligned with each other to simplify framing. We will be using CertainTeed Optima Blown-In Fiberglass Insulation in this 9″ thick wall that will result in a minimum of an R-38 wall. The 2″ separation of the studs will remain at the window and door openings, with the windows & doors being installed on the exterior wall. One could argue, and I would, that this reduces thermal bridging levels below SIPs benchmarks as most SIPs still include 2x rough openings that run from exterior to interior layer of OSB.

If you are thinking that we are foolish for not staggering our studs, I have included this lovely diagram for you above. This diagram is taken from a study done by the Consortium for Advanced Residential Buildings or CARB. These bright people had the same question we all have about double stud walls late at night – should we stagger these studs or not? They used state of the art heat tranfer simulation software to develop 10 different THERM models of double stud wall designs. The five with aligned studs are shown above.

The results are that staggering the studs on our 9″ wall would result in an increase in R-value of less that 0.5. Even more interesting is that the 7″ wall with touching studs will only reduce the R-value by 1.0 compared to including a 1″ gap.

Advanced Framing Techniques / OVE

Next, we have employed some typical Advanced Framing Techniques or Optimum Value Engineering (OVE) into our latest envelope design.There are many benefits to using OVE framing techniques, that sadly, most builders have no interest instituting into their buildings simply because it’s not what they’ve done for the past decade or so… Some of the basic advantages include reduce cost in lumber, reduced framing waste and improved energy efficiency due to higher levels of insulation.

There is a beautiful diagram below that illustrates some of the key framing strategies. Here is the list we are using:

1. All framing is on 24″ centers with floor and roof trusses in alignment with wall studs. This reduces thermal bridging and increases the overall wall R-value as more insulation can fit into the walls with less studs.
2. Two-stud corners are used to again reduce thermal bridging at critical corner details and pack in more insulation.
3. Right-sized headers and insulated headers can greatly improve insulation values at leaky window and door sections. We will be using 2×4″ and 2×6″ insulated headers at most windows and doors compared to the standard 2×12″ uninsulated header used by many builders.
4. Hanging floor joists from top plates – We actually improve on the detail shown below by eliminating the often leaky and poorly insulated rim joist detail completely.

That’s it for now on our new envelope design. We’ll get into more detail as we build the homes. If you’re thirsty for more details, the links below are some great sources that were used in the writing of this post.

Source Documents:

• Toolbase Advanced Framing Techniques (check out PDF also)
• Dept of Energy – Advanced Wall Framing (PDF)
• CARB News – Double Stud Walls: Staggered or In-line? (PDF)

Yesterday we looked at some lessons learned from our aggressive air sealing goals on the Passive Project. In doing so we mentioned that we will be utilizing building gaskets and air sealing tape to help obtain the very difficult building air tightness goal of 0.6 ACH @ 50Pa that is required by the Passive House standard. Let’s take a more detailed look at the technology and economics of these two construction materials that are less than standard in the average US home.

Building Gaskets vs. Construction Adhesive

Over in Germany where the Passive House standard originated, they have been using rubber building gaskets for over a decade rather than typical construction adhesive that is used in the US building industry. These gaskets are usually made of EPDM and are similar to the ones used in automotive applications. These gaskets offer a far superior seal for water and air infiltration in difficult and uneven joints like wood to concrete and even wood to wood connections.

I just stumbled on a company in Baltimore, MD – Conservation Technologies – that carries a whole host of these German inspired building gaskets, along with a whole bunch of other cool building products for earth loving projects. They have a whole list of reasons why their gaskets are better than caulk or foam that is typically used in the US. Below are the Pros and Cons that we see:

Pros of Building Gaskets

• Superior seal to caulk and foam gaskets or adhesives for both water and air infiltration, especially on uneven surfaces.
• Gaskets will last forever with no deterioration.
• The installation is easy to perform and easy to verify whereas caulk or smaller foam gaskets are very difficult to verify proper application once the walls are secured in place.

Cons of Building Gaskets

• Cost premium (see below for analysis)
• Limited availability
• Construction crew resistance to new technology that is clearly awesome and being used in the rest of the enlightened world for the past 10+ years.

Cost Analysis of Building Gaskets vs. Construction Adhesive

I’ve compared the raw material cost only of two applications of the gaskets. The first is a gasket that would go on a 2×4 to be used at a sill plate location or between the first and second floor of a house. The other is an interior application at the drywall to wood connections. It’s clear that the cost is 2-3 times that of conventional construction adhesive. Some may claim this is expensive, but I was happy to see that the cost difference was not much higher.

2×4 Building Gasket = $0.44 per linear foot
Double Construction Adhesive = $0.15 for two lines per linear foot (1/4″ beads with 10% waste per tube)

Drywall Building Gasket = $0.16 per linear foot
Single Construction Adhesive = $0.075 per linear foot (1/4″ bead with 10% waste)

If we were to take one of our standard building footprints of roughly 18′x40′ that would mean our perimeter is 116′. We would use at least three instances of the 2×4 gasket at the sill plate, second floor and roof details for a total of 348′. Using gaskets rather than a double bead of construction adhesive would add roughly $100 to our material costs. Not bad at all for extreme confidence in a good number of our critical air sealing junctions. Not bad at all.

Air Sealing Tape Analysis

OK, we’ve looked at gaskets, now lets look at using a whole bunch of tape to seal the seams in our sheathing prior to installing our WRB. This seems extreme to most, and maybe it is, but man does it look good. It also seals a building up really nicely for very little additional non-skilled labor. I mean, we can all handle a roll of tape.

Passive House people love this Grace Vycor Tape for their OSB air sealing. I’m sure there are many other butyl based tapes out there that are similar and just as effective, but we will use Grace Vycor for our example. It can be found online in 6″x75′ rolls for about $24 which is not cheap, but certainly is not a bad deal for such a lovely product.

Our homes are small and infill, so we have two facades that are roughly 18′x25′ to be taped. This equates to 900 square feet with roughly 12′ of tape needed for each 32 square foot sheet or sheating (only two sides need tape as the others will overlap other sheats). This gives us $337 of tape needed. Let’s go ahead and round that up to $500 for extra tape needed on corners, windows and door openings if we are so inclined. While this is more expensive than the gaskets, it’s still manageable and should go a very long way to reducing air infiltration in our homes.

So there you have it. For less than an extra $600 in material costs and negligible labor additions, we have created a very air tight envelope that is easy to inspect and verify. Your costs in detached homes will obviously be larger, but they should still be in line percentage wise with your build costs as you are already used to buying more sheathing, cladding and the like. Offer your thoughts on these material additions to traditional builds in the comments and thanks for reading.

It’s been a while since we posted on any technical aspects of the Passive House we are trying to build in the Passive Project. We recently tested our air sealing with a blower door test prior to drywall at the homes and I figured it would be a good time to bring up some thoughts on our current air sealing methods along with future ideas we plan to implement.

Last time we spoke about air sealing was when we looked at our foundation and slab insulation and under slab air sealing. Since then we have obviously finished framing, sheathing and cladding the homes. Let’s recap our basic air sealing strategy since these posts on the foundation.

Above Grade Air Sealing Techniques on the Passive Project

1. SIPs walls and roof – Review SIPs Construction Details and notice how much sealant they spec in the assembly of a SIPs building. This along with the SIPs themselves, makes for a much tighter home than an average stick built home. We improved our sealing details from experience gained on the 100K House installation.
2. The poly air barrier from beneath our slab was wrapped up inside the house and continuously taped to the interior of the SIPs walls to eliminate air leakage at the critical junction between slab, foundation wall and first floor framing.
3. A Tyvec air and water barrier was installed on the exterior of the walls. All seams were taped and all windows and doors were taped, caulked and foamed to the Tyvec barrier. Normally people don’t tape the seams. We made sure each seam was taped.
4. Tyvec was all used in between the homes at the party wall as seen in the image above. All seams were again taped, and this layer was wrapped around to the facades and to the roofing membrane to form a continuous barrier.
5. The typical rubber roof acts as our air barrier on the roof.
6. Each penetration through the slab or roof was taped and foamed to its surrounding air barrier with a detail similar to the one shown below.
7. A wireless electrical switch in combination with floor outlets along the interior facades of the homes, eliminates electrical penetrations through the SIPs walls.
8. All LVLs were designed not to penetrate any exterior walls to maintain the airtight SIPs walls.
9. All joists and rim boards were hung internally to make for a simpler and more airtight exterior wall construction.
10. All drywall is glued to the interior of SIPs and framing.

This is a long list and if I had to pick the most critical out of this, I’d say it is the SIPs, the under slab poly wrapping up to the SIPs and the envelope penetrations as the key details that are significantly different from normal construction. The Tyvec layer inbetween the two homes was also not the easiest sell to the construction crew.

We implemented all these items to the best of our ability, but mistakes were made along the way. It’s hard to tell where sealant or tape may not have been applied as needed. These omissions have resulted in a lower than desired tightness at our pre-drywall inspection. We’re not exactly sure of the actual result due to some HVAC and electrical openings that were not completely sealed at the time of the test, but we think we are somewhere in the range of 3-5 air changes per house at 50 Pascals of pressure. Our ultimate goal in the Passive House standard is 0.6 ACH @ 50Pa, so needless to say, we are doing our best to patch and caulk any and all air leaks that we found during the test.

The biggest lesson I’ve learned from both building the Passive Project and attending the recent Passive House Conference in Urbana, Il is that this 0.6 ACH @ 50Pa target is by far the hardest spec to achieve in the Passive House standard. I would say it’s even harder for a production builder to achieve in an environment that does not allow extra time and budget to fix some errors along the way. An owner/builder can decide to add another month or three and a couple grand to their budget to make air sealing changes on the fly. A production builder needs to have their plan bulletproof from the beginning and execute it to the T or the entire construction schedule and budget will be thrown out the window trying to recover.

Key Airtight Construction Lessons Learned

• Design multiple layers of air sealing. There should be one primary line of defense against air infiltration in your envelope assembly (A red line drawing), but you should not stop there. Take every opportunity to air seal anything you can from the outside to the inside of your walls and roofs. I have Mr. Hayden Robinson to thank for this advice at the Passive House conference. I was pleased to see him present on his latest Passive House design that looks almost identical to the planned construction on the Skinny Project.
• Design simple to implement air sealing details. If a crew is completely unfamiliar with a certain product or method, then sometimes it is best to re-think a detail. If everyone can understand the detail and believes it will be worthwhile to install, there is less chance of corners being cut when someone is not looking on the job site. Sometimes it is also better to spend more money on a better product that will reduce labor costs when time and budget are a concern.
• Design easy to inspect air sealing details. It is kind of common sense, but it makes sense that it is easier to require strict air sealing if it is easy for your forman to inspect the critical details during assembly and preferably after assembly. If a gap can be caught easily at the end of a daily inspection before it is covered up the next day, you’re going to end up with a much tighter house in the end for the least cost.
• Document your critical air sealing details well. This sounds logical, but most air sealing details can get lost in the mix when surrounded by many other structural and material details and callouts. We prefer to have specific diagrams on separate 8.5×11′s that can be made into a book to reference on the jobsite. These details get down to the very basics of the critical air sealing materials and junctions. They can also be blown up much larger than normal when placed on their own page.

OK, now that we’ve covered that, we can move on to what we are planning for the next project in terms of air sealing. As we have heard, we are going away from SIPs on the next project (dang, I need to post on why) so we have our work cut out for us.

Future Air Sealing Construction Strategies

1. Document each critical air sealing detail on it’s own 8.5 x 11″ page for easy reference at the construction site as stated above.
2. Tape all seams in exterior sheathing with Grace Vycor Tape.
3. Install an one way air tight Water Resistive Barrier (Tyvec, VaproShield…) and tape all seams over the sheathing.
4. Use Conservation Technology Building Gaskets at all critical wood to wood and wood to concrete connections while framing. I love these gaskets and will write an entire blog post later on why. They rock.
5. Apply construction adhesive liberally at all wood to wood connections near the exterior sheathing where gaskets are not used.
6. Install Conservation Techonology’s Drywall gaskets on interior framing to provide an airtight seal once drywall is applies without having to install costly poly or similar air sealing barrier.
7. Use rigid XPS insulation with taped seams as air barrier on basement walls that connects to sheathing above and underslab insulation and poly below.
8. Use specialized double sided butyl tape of window gaskets to seal around windows and doors in addition to spray foam. I haven’t made up my mind on the best method here. Gaskets are great and I think the tape is even better but only found in Europe right now.
9. Use Protecto Wrap’s Dual Guard Threshold Tape under all door thresholds. This is a nasty area where metal is usually meeting concrete and just doesn’t seal well.

Well, I think I’m spent on this post. I apologize for the lack of diagrams. They will follow hopefully in future posts. Please add to my lousy lessons and ideas in the comments below and I will try to participate as much as possible.