We have started to explore larger projects with our development company in Philadelphia that include shared off-street parking lots with a common driveway. This provides a new opportunity to explore more sustainable pavement options than the traditional blacktop used in most projects. Part of our research, as always, is devoted to finding the best mix of sustainability and cost so that we, and others like us, can actually have a chance of implementing something new on a for-profit project.

First, a bit of quick background on how Philadelaphia’s Water Department is actually encouraging projects to use permeable pavement in larger projects. In Philly, the city requires projects that exceed 15,000 square feet of area to develop an approved Stormwater Management Plan. Typically this involves large underground detention basins and extensive piping. There is also a lengthy design process typically associated with the Philadelphia Water Department.

Fortunately, the PWD provides incentives to builders to fast track their design and approval process for stormwater management if they can satisfy the needs via “green” methods. This typically always includes some type of pervious paving surface where impermeable would typically be installed and a method of delaying roof runoff from entering the city sewers (think green roofs or giant rain barrels).  Yea Philly!

OK, now on to the different options available in pervious surfaces that you can drive a car or even a large truck over. We’ll cover the main types that we have run across and you can tell us what we’ve missed in the comments. All of these systems are installed in a similar fashion. There is often a bit more excavation and up to a foot of crushed stone or gravel installed prior to the paving surface in order to help facilitate collection and storage of large rainfalls without the surface experiencing flooding. Simple, smart and effective. Read on and enjoy my rating system.

Porous Asphalt (Blacktop)

That's a fancy stream of water!

Porous Asphalt, or Blacktop as the kids say, is one of the more popular options out there as it seems to be the most cost effective and widely accepted. After all, it looks pretty much like normal blacktop and asphalt is king for most of our roads and parking lots.

Cost – $
Maintenance – Lots
Porosity – ~176″/hour
Ability to Grow “Green Things” – 0 out of 5
Overall Sustainaearthgreenfriendliness – D+

The Asphalt starts out strong with low cost and effective porosity, but quickly loses points for requiring a lot of maintenance, zero ability to grow anything, being nasty and a strong contributor to the urban heat island effect. Don’t get us wrong, it’s much better than standard asphalt. We’d just prefer one of the other alternatives a bit more for smaller projects that don’t include thousands of miles of roadways.

The maintenance we are talking about is a biannual cleaning with a giant commercial vacuum type device to keep the voids in the blacktop from getting clogged over time. Sweeping or pressure washing won’t do and may only contribute further to premature clogging. Check out the National Asphalt Pavement Association for more info.

Pervious Concrete

Oooooooooh!

Pervious Concrete is the same concept as porous asphalt, except it’s concrete. It’s very easy to order and have installed by a skilled flatwork contractor, even if they have never used it before as it is basically normal concrete with no “fines” in it. This is how it remains open to water infiltration. A benefit over asphalt is that is will result in a much lighter color that will not contribute to the urban heat island effect as much. It is still concrete though and comes with the carbon footprint associated with concrete if you’re counting carbon points on your project. A bit costlier to have installed than porous asphalt, it is a choice we prefer if options are limited.

Cost – $$
Maintenance – Lots
Porosity – ~480″/hour
Ability to Grow “Green Things” – 0 out of 5
Overall Sustainaearthgreenfriendliness – C

One way to reduce your carbon footprint with any concrete order is to insist on local or even reclaimed aggregates and push for the highest amount of Fly Ash and/or Slag which are both reclaimed waste products. Pervious Concrete also requires the same biannual sucking that porous asphalt recommends. Check out PerviousPavement.org for more info on Pervious Concrete.

Pervious Block Pavers

Most commonly seen permeable concrete paver

There are many different types of Pervious Block Pavers popping up on the market now that the concept of saving the earth is gaining popularity again. The most commonly seen permeable paver is shown to the left and creates a hexagonal shape of concrete around a central pocket where grasses can be planted or simple gravel can be filled in.

Cost – $$$
Maintenance – Some
Porosity – Varies
Ability to Grow “Green Things” – 3 out of 5
Overall Sustainaearthgreenfriendliness – B+

That tire is really working up a sweat.

Since the popularity of this interlocking concrete paver had increase, more varieties have hit the market that look more like traditional pavers. An example is shown to the right. These pavers have less open area that is usually created either at the corners or by spacing the pavers on all sides to allow for infiltration. This type of paver can not grow anything in the voids, but is typically filled with gravel. It’s a nice option for those that want the traditional paver look with boosted functionality.

Tbe biggest deterrent to these types of pavers is the cost. Not only are the pavers themselves pricey, but the cost of install is typically much higher than the other varieties of permeable paving due to having to lay individual, small blocks by hand. There can be some maintenance with these pavers as they may individually settle or become misplaced after some use. They may also be damaged easier than a uniform pavement by snow removal in the winter. There are too many suppliers of these products for me to point to one source, but Google can help you out if interested in more info.

Drivable Grass

Drivable Grass with grass, sand, gravel & mulch filler

Drivable Grass is a specific product manufactured by the Soil Retention company. It’s kind of a unique product that we recently stumbled across at Greenbuild that I felt deserved it’s own category. The product melds a bit of the benefits of the other products into one system.

For starters, is comes in 2′ x 2′ mats that are much more affordable to have installed than the individual pavers. It also has a much larger exposed area (61%) for greater infiltration and more room to grow grass or ground cover in if desired. Also, unlike the traditional hexagon turf pavers, this system does not isolate the plant material into individual pockets. This allows the plantings to remain cooler and receive more uniform watering. These benefits result in a greener parking surface than most of the alternative plantable systems.

Cost – $$
Maintenance – Very Little
Porosity – I couldn’t find a spec. Sorry.
Ability to Grow “Green Things” – 4 out of 5
Overall Sustainaearthgreenfriendliness – A

Currently, this is our top choice to use in a few of the sites we are looking to develop in Philly that have shared parking areas. It looks like the cost will be less than permeable concrete and we will get the added benefit of creating a green space in the parking lot that requires much less maintenance than other systems which will reduce the HOA fees for the home owners. All good things so far.

Plastic Grid Systems

Yes, you can drive on these plastic cup things

Cost – $$
Maintenance – Very Little
Porosity – Lots
Ability to Grow “Green Things” – 5 out of 5
Overall Sustainaearthgreenfriendliness – A

Last but not least are the plastic grid varieties of permeable paving systems. Some of these get extra points for being made of recycled plastic and being fully recyclable themselves. We have done the least research on these systems, but the install seems straightforward and it can result in a fully sodded surface if desired. The main issue we saw was that it is recommended for light or occasional use parking lots if you want to maintain the grass on the site. If anyone has any experience with this type of product, please speak up in the comments.

Conclusion. That’s all I have. Contribute below.

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.

Over 1 million Energy Star Homes have been built to date in the US. Compare this to just over 6,500 LEED Certified homes and probably less than 20 Passive House Certified homes in the US. While Energy Star is much less stringent than the latter certifications, it is easy to see which standard the bigger production builders are turning to first in an effort to respond to the market’s demand for more environmentally friendly homes.

An Energy Star Home is basically trying to achieve 15% higher energy efficiency overall when compared to the same house built to code minimum standards. Our big two questions when forming Hybrid Construction were, “Is 15% efficiency improvement over code enough?” and “How many of the builders out there are just barely squeaking by with very minimal changes to the design of their old homes?”

There are some builders out there knocking the socks off of Energy Star standards, especially those participating in programs like the US Dept of Energy’s Building America and Builder’s Challenge programs (see chart above). This is swell, but for every builder that is far exceeding the minimum standards, there are probably 5-10 others that are doing the bare minimum to pass. We won’t name names, but we’ve heard a few stories of decent sized local builders completely missing the mark on large developments where Energy Star Certification had been advertised to consumers from the beginning. Insert embarrassing failure sounds here.

On to the point of this post. When we decided to launch our new construction company, Hybrid Construction, we realized that not everyone would have the need or desire to build to LEED or Passive House levels of construction. Therefore, we turned to Energy Star as a suitable target for our base level option in any Hybrid home that we are hired to build. When we sat down to think about it further, we realized that just hitting the minimum Energy Star goal would not be enough to satisfy the Hybrid brand’s base level of homes. Here are some of our main brainstorming points:

1. If we’re going to build an energy efficient home, let’s not stop at 15% better than code, but target 20% – 30% reductions.
2. If we’re guaranteeing Energy Star Certification, we need to target greater than 15% no matter what.
3. Energy Star is missing some key subjective elements that can not be ignored in Hybrid’s base homes. Things like type of windows and the use of really nasty materials like vinyl.

Below is a chart that we ultimately came up for the entry-level Hybrid 1.0 Energy Star house that includes items we felt any budget energy efficient home should be built to in the climate zone surrounding Philadelphia, PA. It is derived from the build levels chart on the Hybrid site, but focuses only on the base (1.0) level. For comparison, Hyrbid Construction just achieved efficiency levels 70%+ below code at it’s 3.0 build level. Below the chart is a bit more detail on the reasoning behind all of the choices.

Insulation Levels and Type

Insulation levels are a core factor in any Energy Efficient home and one that is relatively easy and affordable to increase beyond minimum standards when building a new home. Energy Star already recommends surpassing their minimums for new construction in their insulation chart targeting people performing retrofits to their homes. Why not follow suit and add a bit more in all new construction homes. It could cost as little as a couple hundred dollars extra in most new homes. If you’re filling your 2×6 wall cavities and 2×12 floor and roof cavities with decent quality insulation, you are there.

In the subjective category, we point out that dense-packed cellulose insulation is Hybrid’s preferred type of insulation. This will add some cost compared to standard fiberglass batts, but it is well worth it for a number of reasons. Fiberglass is not an option for Hybrid mainly due to it’s poor performance compared to cellulose and it’s high embodied energy. Customer satisfaction is very high with cellulose and it goes a long way in differentiating a house from all of the other traditional Energy Star homes out there.

Air Sealing & Windows & Ventilation

These categories are lumped together as we’ve learned in our research during Hybrid’s formation of what typical builders are doing. Most production homes in the US have inexpensive, vinyl double-hung windows. These are too leaky for Energy Star, so people are switching to single-hung which are a bit tighter. The single hung, however are still leaky enough that a builder can simply install an energy star bath fan and set it to run continuously to achieve the ventilation standards of the Energy Star guidelines. Stale air is sucked out and fresh air is simply brought in through the leaks in the windows and the rest of the house. That means that if it’s 20 degrees outside, that’s the temperature of the fresh air being transferred into your home 24/7.

Since poor air sealing can account for over 30% of a typical home’s energy costs (especially if insulated with fiberglass), we we felt that Hyrbid should take this pretty seriously in all levels of its builds. Most Energy Star homes get a $350 air sealing package from their insulation installer that basically includes spray foaming around key penetrations and stud to sheathing connections before installing the insulation spec’ed. Hybrid will do that also, but take it quite a bit further by adding the following:

• Taped exterior ZIP wall and roof sheathing
• Taped OSB subfloor
• Continuous sealant at critical rough framing junctions
• EPDM sill gaskets
• Gasketed interior to exterior penetrations (ie. plumbing stack)
• Foamed, caulked and taped Window & Door installations

Casement windows have much tighter air sealing components that do not loosen up over time when compared to double hung. They also have a more contemporary look while allowing more light and ventilation into the house. Now that the house is so tight, Hybrid will add a Heat Recovery Ventilator for about $500 that bolts directly onto the ductwork for the heating and cooling in the house so that unconditioned air is not being pulled directly into the house. A few minor and inexpensive improvements that have a big impact on the efficiency and quality of the house.

HVAC & Water Heating

We won’t go into a lot of detail here, but we want Hybrid to install components that are slightly higher in efficiency than the base Energy Star requirements without breaking the budget.

When it comes to hot water, using either an electric heat pump unit or a high efficiency gas tankless unit should blow away the Energy Star minimums for a few hundred extra dollars when compared to a minimum efficiency tank unit of the same fuel.

Heating and Air Conditioning is best done with a dual-fuel system in a typical home that has gas. A high-efficiency heat pump will handle the majority of the heating and cooling requirement, while a high efficiency gas furnace will supplement the heating demand on the coldest days of the year. Hopefully the increased efficiency of the home’s envelope will allow the budget to recoup some of the premium for the higher efficiency units by allowing a smaller unit to be spec’ed.

Appliances and Lighting

It’s hard to not buy Energy Star Appliances these days. We’ve found the key to going a bit farther than the competition is by spending a lot of time on the Energy Star site pouring through the appliance spreadsheets for refrigerators, dishwashers and clothes washers.  Often the smaller, no-frills appliances are much more energy efficient (and cheaper) than some of the more popular large appliances that may just not be needed by the end client. Notice it says “needed,” not “desired.”

Lighting for Energy Star is interesting in that you don’t need to install a single CFL to get Energy Star certified if you make up for it in your appliances. With lighting accounting for over 10% of a home’s energy usage (which will only go up as a home becomes more efficient) this is low hanging fruit. Put those CFL’s everywhere. The end home owner can replace any lights that may really annoy them or add their own lighting fixtures after they move in. By the way, CFL’s come in three color spectrums – soft white, bright white and daylight. Choose your favorite.

Subjective Issues Outside of Energy Star

Energy Star does not cover certain aspects, that we felt were important when forming Hyrbid, to any new home trying to position itself as both energy efficient and sustainable. The biggest glaring omission is water efficiency. It does not cost any more to add low flow bathroom fixtures and Water Sense toilets to a new house, yet it can have significant impact on the total water usage. By reducing water usage, specifically in the shower, you are also greatly decreasing the energy used to heat domestic hot water. Two birds, one stone…

Another category that adds no cost to a new home is using Low-VOC paints and finishes in place of toxic, off-gassing finishes that are used in typical homes. The homes will smell fresher and be healthier for your clients from day one, so there is no reason not to include this with any base Energy Star home. See the American Lung Association’s Health House certification for more on the benefits of healthier indoor air quality if you’d like to go to the next level and differentiate yourself further from other base Energy Star builders.

Last, but not least, we try to limit the use of toxic vinyl products in the home as much as possible. This means using fiberglass or aluminum clad wood windows over vinyl which also increase the home’s value. Another big one is vinyl siding, which is not only toxic, but hideously ugly and cheap in appearance. Try a durable fiber cement product that has a better appearance, includes a 50 year warranty and contains over 25% recycled content. Certainteed happens to make our favorite fiber cement siding that’s available in the US residential market at a very affordable price while also locally made.

Conclusion

Compared to the rest of the wealthy countries of the world, we have been building fairly lousy houses on average here in the US. The Energy Star program is a great tool to affordably improve the standard of new homes, but is it enough? Do you want to be another builder or home owner just scraping by minimal standards that most other countries would accuse of being way too lax in terms of energy and durability? Do you want to risk missing a new target because you’re aiming too close to the goal and only a few mistakes will cost you your reputation or a lawsuit? We all need to work together to deliver higher quality housing that beats standards like Energy Star by a healthy margin, while discontinuing the use of cheap and toxic building practices and products.

Do you have a different viewpoint? Don’t be shy. Share it with us in the 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)