Hold the Foam! This Home is Already High Performance!

Before spray foam insulation was installed in the walls and roof-line of this Atlanta-area home, it tested better than the 2012 IECC requirements in climate zones 3-8 for building envelope tightness.

The High Performance Home

Several weeks ago we reported that the Proud Green Home at Serenbe, built by the Imery Group, achieved a blower door (air leakage) test result of 0.70 ach50 immediately after spray foam was put in to the walls and roof-line, and just before the drywall was installed. That's 10 times better (less) than maximum allowed by the current 2009 Energy Code (7 ach50), and more than 4 times better than the not-yet-adopted 2012 Energy Code. When the house is finished, we will perform the final blower door test, and we expect to be even tighter.

Recently, we performed two similar tests on a home in Decatur, Georgia (built by Arlene Dean Homes). Instead of waiting for either the foam or the drywall to be installed, we first tested the home before the open-cell spray foam was put in to the walls and roof-line. Our second test was just after the foam was installed. We expected the foam to fill many of the gaps and cracks, but testing before gave us an idea of how tight or leaky (half-full, half-empty) the house was before the foam. The follow up test (about a week later), when the foam was installed, showed us how much the foam contributed to the tightness.

Both the Serenbe and Decatur homes were built with conventional advanced framing techniques, using 2x6's spaced at 24" o.c. for the above grade walls, and either engineered trusses or I-joist for the floors and roof. On the outside of the above grade walls, an insulated sheathing product  was installed. These 4x8 sheathing panels are like an open-faced sandwich made up of an exterior layer of ZIP System OSB wall sheathing, and an interior layer of either 1/2" or 1" polyiscyanurate rigid foam.

All joints, seams and penetrations were sealed with tape. Then, a ventilated rainscreen was installed over the sheathing and behind the cladding. In an earlier post, we discussed how this assembly performs like a "Perfect Wall" (J. Lstiburek, Building Science Corp). The roof was sheathed with ZIP System Roof Sheathing, and all window/door openings were properly sealed with a combination of tape and low expansion foam. All the wall and roof framing cavities were then filled with an open-cell spray foam. Below grade walls for the Decatur home were 8" concrete, with continuous exterior rigid foam and closed-cell spray foam within the framed cavities on the inside.

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The Test

Since we were testing the Decatur Home so early on, things like the duct for the range hood, bath fans, and plumbing stacks needed to be sealed off to simulate actual conditions when all appliances and fixtures are installed.

The blower door test we performed on the Proud Green Home was a single point test. We de-pressurized and pressurized the house to a single pressure "point" of 50 Pascals, and then converted the results in to a metric common in the home performance industry and in current energy codes, ACH50.

For the Decatur home, we ran what is called a "multi-point" test. This means that we de-pressurized and pressurized the home at 5 different pressure points (10 Pa, 20 Pa, 35 Pa, 50 Pa, and 75 Pa), and used the average of the results to come up with a more accurate conversion to ACH50. We took the readings from each point, along with required building data (e.g. square footage, volume, house pressure, etc.), and entered them in to a software called TECTITE. The software performed all the calculations and conversions, and immediately give us our results.

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The Results

As mentioned above, the 2009 IECC, which is adopted by most states, requires an infiltration rate of less than 7 ACH50. The 2012 IECC, which is adopted by only one state, requires 3 ACH50 or less. Below are the results of our tests performed before and after installation of foam. As you will see, the house tested pretty well. Before foam, the house is below 2012 IECC requirements.

Negative Pressure without Spray Foam - 2.71 ACH50

Positive Pressure without Spray Foam - 2.84 ACH50

Negative Pressure with Spray Foam - 0.89 ACH50

Positive Pressure with Spray Foam - 1.09 ACH50

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Opportunities...

What could have been done to make the house even tighter before foam?

When we walked through the house before and during the tests, we noticed that there was no blocking or sealing done between trusses on the second floor. Most of the leakage we detected (with smoke stick) was coming from this area and one other, at the connection between the stepped foundation and the above grade walls.

If more attention had been paid to these areas, the results could have been as low as 1.5 ACH50 or less.

Note that none of the air sealing in this home was done using caulk. Tape has proven to be a very effective way to air seal, and it's almost exclusively used in many Passive House projects.

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P.S. 2012 IECC and the R-20 Wall

Right now, under the 2009 IECC, putting R-13 insulation in the wall cavities is the requirement. When jurisdictions in Climate Zones 3 and 4 adopt the 2012, all above grade walls will need to have a minumum R-20 wall assembly. Both the Decatur and Proud Green Home meet this requirement with a standard 2x6 wall with a full cavity of insulation, and ZIP System R Sheathing with it's continuous layer of either R-3.6 or R-6.6 rigid insulation (Total: approx. R-25.6 or R-22.6).

If you're interested in reading about whether the 2012 IECC will cost more to do, or actually save us more energy and money that we spend to meet it, here is a website with the results of a study done for the Department of Energy showing what a home built to the code in most states will potentially save. There's a downloadable report for each state.

Here's the one for Georgia, where both of these homes were built.

Georgia Residential Cost Effectiveness 2012 IECC

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