Near Perfect Air Tightness Measured in Contemporary Home

A discussion of a near perfectly airtight contemporary home in Marietta, GA, the testing, the results, and how it was achieved.

The blower door is set up in the front door of the Contemporary High Performance Home in Marietta, ready for the pre-rough-in infiltration test.

NEAR PERFECT AIR TIGHTNESS

The tightest building envelope we have ever designed or built was our own Tiny House project in Florida. It had a volume of 6,000 cubic feet and a surface area of approximately 2,000 square feet. The final air leakage test (measuring infiltration and ex-filtration via a blower door) results showed an air exchange rate of 0.4 ACH50 (Air Changes per Hour at 50 Pascals). This means that if the house is under a pressure equivalent to a 20 mph wind blowing directly on all sides of the building, then 40% of the volume of air inside the house would leak through the cracks and gaps in the span of one (1) hour.

We also ran a blower door test before and after the rough-in stage of the project, when the plumbing, HVAC and electrical subcontractors would cut holes in the building shell (a.k.a. enclosure) for their pipes, wires, ducts, etc. We do this in order to measure how well we installed the air, water, and vapor control layers, and sealed the penetrations before installing the continuous exterior insulation (thermal control layer) on the exterior of the enclosure. The results of these two leakage tests were the same for the Tiny House, which means we perfectly sealed the penetrations! The leakage at both stages was 0.2 ACH50.

At the time we tested the Tiny House, the Florida Energy Code allowed a maximum infiltration rate of 7.0 ACH50 at final testing, which is 1,750% higher than what we achieved.

Section of the our Tiny House we designed and built in Florida, with continuous uninterrupted building enclosure

The smaller the volume of a building, the more difficult it is to achieve a low leakage rate like the Tiny House. For example, when the house is under 50 Pascals of pressure (during blower door test), 2,400 cubic feet of the air inside the Tiny House is exchanged with outside air in one hour. That's not a lot of air. On a house with 25,000 cubic feet of volume, like the Contemporary High Performance Home we're now building in Marietta, GA, the same result (0.4 ACH50) would mean that 10,000 cubic feet of air leaks in one hour under 50 Pascals of pressure. That is four times the amount of air than the TIny House exchanged during the test. If we were to add up all the cracks and gaps and make a single cumulative hole, using the Effective Leakage Area calculation (CFM50/18), the ELA (i.e. the hole) in the Tiny House would be smaller than the Marietta home.

THE TINY HOUSE MAY HAVE MET ITS MATCH

This past Friday, we performed the pre-rough-in air leakage (Blower Door) test of the house in Marietta, and the tightness of the enclosure pushed the limits of the testing equipment. On the smallest stock settings of the equipment, the gauge that reads the airflow in and out of the enclosure while the building is under negative pressure, read "TOO LOW". This meant that the actual leakage is even lower than what the gauge could pick up.

The gauge (manometer) can read as low as 50 CFM50, when used with a standard blower door fan before it flashes "TOO LOW". When paired with a smaller duct tightness testing fan, the gauge can read as low as 10 CFM. For the next leakage test, the energy rater, David Wasserman, will be using that smaller fan to get a more accurate result.

If we were to accept the results we got using the larger fan, 0.12 ACH50, the house would leak 3,000 cubic feet of air in one hour under 50 Pascals of pressure. When we test with the smaller fan, I'm predicting that the result will be between 0.05 and 0.1 ACH50.

FOG FINDS LEAKS

While most builders would be more than satisfied with a result this low, we need to know where and how big the gaps are. Where there's a leak, there's a path for unwanted bad air and moisture to get in, and good conditioned air to get out. If large enough, it's also a path for critters (insects, etc.).

To find the leaks, we used a small fog machine that you might find at a performance theater and filled the house completely. We then switched the direction of the fan to pressurize the house, forcing the fog out through the cracks. This turned out to be very effective.

We walked around the house looking for fog, and found trickles coming from around a few windows, and at the wall-to-roof transition, but found that most of the leakage was happening at the blower door frame that is installed in the front door. In fact, there was a surprising amount of fog pouring out around the frame.

The fog also showed a surprising amount of leakage at a swinging patio door that was installed the day before. After we double-checked that the door was closed and locked properly, we noticed it was still leaking more than we expected. All of the windows and doors are by Marvin, and we have never had anything of theirs leak that much. So, we took videos and pics and moved on. Later that day, the window/door installers came by for a follow-up and discovered that the door was missing shims, which caused the door to not seat properly within its frame. This opened up a relatively large gap on one side of the door that easily explained the leakage.

The leakage at the blower door frame will be addressed by doing a better job of sealing the perimeter where it meets the door opening, and the identified leaks will easily be plugged before the next air leakage test after rough-in. The swinging patio door will be pulled out and reinstalled, with shims! 

Assuming our estimate is correct that using the smaller fan will result in leakage between 0.05 ACH50 and 0.1 ACH50, the total amount of air leakage in the Marietta project will be less than the Tiny House. At the lower end of that range, the amount of air leakage will be 1,250 cubic feet of air in one (1) hour, which is half that of the Tiny House.

HOW WE ACHIEVED NEAR PERFECTION

The house is a wood-frame house on a slab-on-grade. The walls and roof are completely sheathed in 1/2" CDX plywood. Over the wall sheathing, we applied a 40-mil thick layer of liquid applied flash and wrap system, called Blue Barrier, by PolyWall, and over the roof sheathing, we installed DeckGuard HT, a peel-and-stick product by PolyGuard.

Slab-on-grade detail for the Marietta project. Where the bottom sill of the exterior walls meet the slab, we installed a continuous EPDM gasket, by Conservation Technologies, and then sealed the joint between the sheathing and slab with PolyWall 2200 Joint and Seam Filler on the outside before covering that joint with a continuous termite-proof tape, TermF, by PolyGuard. The 2200 was also used at all plywood seams and to cover every nail.

Where the bottom sill of the exterior walls meet the slab, we installed a continuous EPDM gasket, by Conservation Technologies, and then sealed the joint between the sheathing and slab with PolyWall 2200 Joint and Seam Filler on the outside before covering that joint with a continuous termite-proof tape, TermF, by PolyGuard. 2200 was also used at all plywood seams and to cover every nail.

Marvin windows installed after PolyWall Blue Barrier System was installed around the entire enclosure

Our painting crew installing PolyWall 2200 Joint and Seam Filler at ever plywood seam and covering every nail.

The painter using a roller to apply the PolyWall liquid applied flashing around the entire structure.

The wall to roof transition of the entire structure is uninterrupted, meaning there are no rafter penetrations. The overhangs will be built on top of the peel-and-stick roof membrane and encapsulated within the 6" thick continuous layer of rock wool on the outside of the roof structure.

This image shows the all different stages of the PolyWall BlueBarrier being installed, as well as the PolyGuard DeckGuard HT peel and stick roofing underlayment.

All penetrations in the slab are sealed with a liquid flashing product from PolyWall, and all doors and windows are sealed with Prosoco's vapor open AirDam sealant between the window frame and the rough opening.

Every penetration in the concrete slab was sealed with the PolyWall joint and seam filler.

Where there was more than one pipe penetrating the slab in the same location, we built a plywood box to pour the concrete to. Later, we removed the plywood box, filled the trough with gravel up to 1/2" from the top of the slab. Then, we covered the gravel with vapor barrier material, and filled the remaining 1/2" or more with the joint and seam filler.

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This project is a design-build collaboration with Jones Pierce Structures. LG Squared, Inc. is the architect of record and the construction project manager for this. For more info on this project and other good practices of architecture, building science and high-performance homes, check out our Instagram, Facebook and YouTube Channel

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Tags: airtight, building, high, performance, science

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Comment by Jose Macho on January 20, 2020 at 5:46pm

My thinking is zip strip sheathing & tape would have been more cost effective which I have seen on passive houses. On one recent house windows and doors were from the UK with built-in leveling which allows precise adjustment as the house settles and framing lumber shrinkage. There is a lot of data from Building Sciences and Fine Homebuilding on passive and near zero air infiltration. I believe the bigger challenge in cold climates is placement and management of air exchange systems. One in particular  in CT the homeowner wanted a gas stove top. An expert was brought in from Germany to design a  pressure boundary in an open kitchen to exhaust the burner gasses/humidity without disturbing the geothermal ducted heating/AC system. I believe there are very few HVAC techs who understand recovery systems and proper placement of ducts.

Comment by Debra Little on January 20, 2020 at 1:43pm

Super impressive detailing and measured performance Chris!

I wonder if there are more health & eco-benefits from using these PolyWall sealants as compared to foam? Lower VOCs, GWP? 

Comment by Chris Laumer-Giddens on January 20, 2020 at 1:21pm

Thank you, Chris,

The door installers use the shims to 1. keep the door level, and 2. to prevent the individual pieces of the frame from bending/warping. The shims on the lower section of one side of the door were missing, and the door frame bowed enough to put the door out of level and create a relatively large gap. Once the shims are in place and door leveled again, the door should be as tight as advertised by the manufacturer.

Yes, the overhangs will be 2x4 outrigger framing that cantilevers between 8" - 18" around the entire home. The design has 2/3 of the outrigger on top of the air barrier and structure, and 1/3 cantilevered past the outside face of the plywood sheathing. We are building the outrigger "structure" so that a single piece of 3.5" rigid Rockwool insulation will exactly fit between the 2x4s. then the remaining Rockwool (2.5") will sit on top of the outriggers/insulation, essentially encapsulating the framing in the insulation. Make sense?

Comment by Chris Laumer-Giddens on January 20, 2020 at 1:12pm

Thanks, Cody,

The crew absolutely did their job well! It was the painter's first time to work with the PolyWall, but they nailed it on the first attempt. The biggest "hurdle" they had to get over was to not think like a painter when it comes to filling the overdriven nails ;-) They wanted to spend a little more time on each one to make it perfectly smooth. No, no, no...

RE: Ventilation - we have a custom ventilation system similar to the one described in this post: https://www.lgsquaredinc.com/post/a-solution-for-fresh-and-make-up-.... The house is, in a way, acting as its own recovery ventilator. Although, I did work with a Zehnder unit before on this project, and appreciate its effectiveness: https://www.lgsquaredinc.com/post/serenbe-modern-proud-green-home-u...

Comment by Chris Dorsi on January 20, 2020 at 10:31am
Nice job Chris. Especially impressive since most builders can achieve this level of air tightness only by using liquid foams. Do tell us more about “missing shims” at the doors. Also, the no overhang does make sense from an air sealing perspective—did you frame overhangs on top of the air barrier? If not, how did you address water control at this leak-prone transition?
Comment by Cody Farmer on January 20, 2020 at 9:56am

Good job! Easy to do too! No silly business from inside and around the studs. No foam and all of what you show can be done by the framers, one team to bonus or penalize when that blower door comes in. I recon these guy got at least a 6 pack of micro brews and a happy hun $$ for that air tightness!  Do you use Zehnder for ventilation? I Like the Termite Details.

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