First modular Passive House blower door test results
Chris Conway and Caleb Fritsch of Conway Energy performed the long-awaited blower door test for our first modular passive house today. We couldn’t have picked a more beautiful — and simultaneously more inopportune — day to have scheduled it. Good forensic testing requires a greater than ten degree difference between inside and outside temperatures so that a thermal imaging camera can “see” the temperature differences where air is leaking. For example, when the interior of the house is cooler than the outside air, leaks coming in will read as orange or red plumes against a blue background during a depressurization test. Conversely, in a pressurization test leaks from within will show up against the outside of the house as blue plumes against an orange background.
Trouble was, on this August day the high was a balmy 78 degrees and we had only been able to get the interior temperature down to 72 degrees with the single window unit we had hooked up to the generator! (The main cooling system could not be run since the house is not yet connected to the grid.)
So the ever-resourceful Chris pulled out his smoke pencils, which were better than nothing. With them you can spot leaks by the change in direction of the smoke as you pass it over a leak. But it is far far more tedious and less efficient that using thermal imaging. We were able to use the camera in the attic space, however, which was well over 90.
It was a nervous moment when Caleb started the fan. The result: .65 ACH50Pa (air changes per hour at 50 pascal of pressure) on our first try. We were delighted with that number, having had no idea what to expect. Chris found enough leaks with his smoke pencil that, in his view, we should easily get below the required .60 ACH50Pa by fixing them.
Most of the leaks were beginners’ mistakes, which we will chalk up to lessons-learned. All are easy to fix:
- The taping of the joints at the first floor subfloor had been damaged by foot traffic in a number of places in the course of the construction. We will re-tape those joints , and in the future we will make sure the subfloor tape is covered by a protective layer during construction.
- The men taping the joint between the top and bottom module had run the tape over the metal straps that connect the two modules, thereby leaving a crack every two feet or so where the tape was discontinuous. This led to a number of leaks around perimeter at that line. It is an easy fix, and avoidable in the future by taping before the straps are bent into place.
- While factory penetrations were all sealed by rubber gaskets and tape, the penetrations made in the subfloor after the house was set were only sealed with foam. Vince will cut the foam back and seal around each of this penetrations with a sealant gun, and tape where appropriate.
- We forgot to tape the overflow holes at bathroom vanity sinks. Right now these are holes to the exterior since the plumbing is not yet hooked up to the sanitary sewer line to the street.
- The attic hatch doorway, provided by Conservation Technologies, was remarkably airtight. It leaked, however, around the rough opening in the framing where in which it was installed. They had used foam to seal that gap rather than air seal tape. Again we will remove enough of the foam to allow a continuous band of tape around the frame.
John Meredith and his crew at Beracah Homes should feel very proud to have achieved this test result on the first try of their very first Passive House. It represents a very meticulous assembly process. To put it in perspective, the leakage recorded today is the equivalent of roughly a 3″ diameter hole in the entire building envelope. Chris reckons that by reducing that figurative hole by 1/4″ we will achieve the .60ACH Passive House standard.
Here are a few pictures from the day…
foamed site-made penetrations at the first floor — the foam will be cut away flush with the floor surface and sealant will be applied around each opening. Same drill will be performed at the bottom surface penetration.
This infrared photo shows the attic floor. Angled lines in the background are the rafters. Those in the foreground are the framing for the midspan rafter support. When we saw that big patch of blue we figured there was a lot of air somehow escaping from the house into the attic. A closer look revealed that the area was still damp from where the solar panel folks must have spilled some water during installation of the panels. The blue is caused by evaporative cooling!
Looking down at the attic floor and the folded up attic stair. The blue shows leaks between the attic framing and the frame of the attic stair unit. This was foamed not taped, and this shows why we prefer tapes.