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.
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!
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.