Sparky Doubled the Air Leakage in this Home!

Sparky Doubled the Air Leakage in this Home

This is the home.


This is the hole that Sparky (electrician) “innocently” made to feed a wire to the light on the front porch of the High Performance Bungalow. I discovered it a day or two after our home performance diagnostics team, Carl Seville and Abe Kruger, of SK Collaborative, wrapped up the first round of final performance testing.
Tiny Hole Big Opportunity

This is Abe, running the blower door equipment, earlier in the construction process, using a modified shroud (the red thing), to accommodate a smaller duct tester fan, as opposed to a full size blower door fan. Why did he use this fan instead of the normal size one?


Because, he knew that we did a blower door test right after we put the finishing touches on the homes continuous air barrier, and before we installed all the cavity insulation and drywall, and the test proved there was very little leakage, and a small fan was enough. For those of you that know the metrics, we tested at approximately 0.95 ach50, at the first test. The goal was 0.5 ach50.

For those of you that aren’t familiar with the metric, 0.95 ach50, or air changes per hour at 50 Pascals (a random amount of pressure) is 13.6% of what the current maximum infiltration (air leakage) that the Energy Conservation Code allows in the state of Georgia, 7.0 ach50, at final testing, when the house is complete and ready for move-in. We reached this before insulation and drywall. 0.5 ach50 is just over 7% of the maximum allowed.

How we did this, was by designing and building the home so that the continuous air barrier is on the outside of the structure, rather than wait to put in on the inside. The house has 2-layers of 1/2″ insulating sheathing (XPS – extruded polystyrene) wrapping the entire house, like a sweater. Together with the windows and doors, this makes up the air barrier. So, if there is any gap, crack or hole in the sheathing, we have leakage. This is why we were so anal retentive about sealing up EVERYTHING, and asked our sub-contractors to PAY ATTENTION. Otherwise, all the efforts would be wasted. The building science would be worthless!


sparky-doubled-the-air-leakage sparky-doubled-the-air-leakage sparky-doubled-the-air-leakage

So, when you have a home as tight as this, a hole like the one Sparky left for the porch light wire can make quite an impact. In fact, it literally doubled the amount of air leakage in the building enclosure. Specifically, the air barrier.

The results, before I found the hole, showed that there was no improvement in the air tightness, from when we first performed a test before cavity insulation and drywall.

Yesterday, we ran the blower door test, again. This time, with that pesky, golf ball size hole plugged and sealed tight. The leakage rate went from approximately 0.95 ach50, to 0.47 ach50. We beat our target!

Compared to the, approximately, 5,500 square feet of surface area that makes up the home, this hole was tiny. In fact it was 0.00028% of the surface area. But, we now know that the total leakage of the home is exactly the same size, since we cut it in half by plugging that darned hole! And, we know that house is keeping unwanted air (and critters – bugs, squirrels, etc.) out, and desirable, comfortable, air (and critters – cats, dogs, etc.) in.

The High Performance Bungalow is a creation of LG Squared, Inc. and Imery Group


4 Responses so far.

  1. Walter Money says:

    I understand the air barrier in Georgia is designed to be on the outside of the wall, well, most of Georgia, anyway. You may consider your location a cooling climate and want to keep all that pesky hot and humid air out.
    I guess my question is why did you use two layers of 1/2 inch XPS instead of one layer of 1 inch, or use polyisocyanurate at the same thickness? Typically, labor is the greater cost over materials, though I admit, not always.
    Also, the Energy Conservatory also has a smaller ring for low flow houses. Would that device have been cheaper to use? How much was the shroud, and where did you get it?
    Walter Money

  2. Walter if I may – no matter your location your primary air-barrier should be on the outside as air getting into the insulation / structure defeats its purpose. Granted as you get further up north most start focusing more on the inside but one should not forget the outside.

    As for two layers – it is a better practice as all things expand & contract. By having two layers offset, any gaps created won’t allow rain, etc… access to the sheathing, etc…

  3. Walter, Sean (@slsconstruction) hit the nail on the head. No matter where you are in the world, control layers to the outside have the potential of protecting everything, assuming proper installation. And, the two layers helps control the air, and the moisture that the air moves with it.

    The thickness is based on climate zone, hygrothermic performance of the assembly, availability, cost, and a more. We had a partnership with Owens Corning, on this project, and they do not make a polyiso. The additional labor of the two layers could be considered cost prohibitive, with an inexperienced crew, but we’re not in a hurry on our projects, and much of the investment that the owners make goes in to a 500-year home, which means durability is critical. This is a good practice, when installing exterior foam.

    Atlanta, and most of Georgia is a heating dominated climate, not cooling. We spend more money heating than we do cooling. Generally, our heating loads and cooling loads are the same, but the heating usually tips the scale. The only time I calculated a smaller heating load was on this house and the Proud Green Home at Serenbe, where our control layers were to the outside.

    No matter what we do, a WUFI analysis is critical. This gives us an understanding of where the moisture risks are in our assemblies, so that we can make adjustments to material type and thickness. This assembly may not be appropriate for every house in Atlanta, depending on cladding, orientation, homeowner occupancy, etc……

    The shroud belongs to our home performance consultants, who already owned it, and the duct blaster. They need it often enough that they made the investment, but I don’t know what they spent. I believe they got it through Energy Conservatory.

    BTW, when considering polyisocyanurate, it’s good to understand that the colder it gets outside the lesser the R-Value. Research was performed by Building Science Corporation to show this:

  4. […] it’s because our home is tighter than tight, or there’s a need to neutralize the negative pressure in the home caused by turning on […]

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