We have passed the preliminary blower door test.

Energy rater Chris Conway of Conway Green Construction visited the site last week with his blower door fan and infrared imaging camera to perform the first blower door tests of our house. It was a critical moment, determining whether all our efforts in taping and sealing had proven effective. It was important to do this before finishes were applied so that we could correct any problems without having to tear out anything.

The blower door testing protocol for a Passive House is quite rigorous. First of all, the number you must reach — .6 air changes per hour (ACH) at a pressure of 50 pascale — means that your building is virtually airtight. .6 ACH at 50 pascale translates to .05 ACH at normal air pressure. In other words, it takes about 20 hours for a single air change in a Passive House, whereas the rate is about 1 ACH for a typical 1950’s brick ranch house.

Second, the way the Passive House Institute requires that ACH number be calculated is more stringent. Whereas, most blower tests divide the total volume of air that escapes per minute by the total gross volume of the house. The PHI requires you divide that number by the net volume of the house, excluding all interior and exterior walls, and all floor framing areas from that gross area, so that you get a much smaller denominator in your equation, giving you a higher number for air changes per hour.

Our results
When we began, we were at about .67 air changes per hour at 50 pascale (As Chris explained to us, 10 pascale is the equivalent pressure to that required to raise the liquid in a soda straw about 1”). We then went around with Chris’ infrared cameral and quickly found a 2” hole that had inadvertently not been sealed and a few cracks under doors. In addition, Panelwrights had deliberately not completed all of the SIP taping so that we could learn what difference the tape actually made. It was clear from the first test and from the infrared imaging that the taping is essential.

After all taping was completed, we went around with the infrared camera looking at every exterior wall and roof surface in the building, finding every tiny bit of air infiltration. After this experience it is clear to me that thermal imaging is absolutely essential in getting a building tight enough to reach the Passive House standard.

What we found
The basement slab and walls were incredibly tight. We found virtually no leaks there, nor were there leaks at top of the basement walls, where the SIP panels bear upon the concrete.

We found several leaks in some of the windows and door. It is likely that these are places where the integral weatherstripping had pulled away from corners.Here is an example:

Differential temperatures between windows and their adjacent walls was between 4-5 degrees, just as expected. This assures us that there will be no drafts at our exterior walls waused by temperature differentials.

We found virtually no thermal bridging in the roof SIP in which we had inset a structural beam. We had set all beams carrying the roof below the SIP panels rather than in the panels in order to avoid  thermal bridging through the panel. In this one case, because of a headroom issue, we had kept the beam in the panel. The infrared image at that beam showed about a 1 degree difference in interior surface temperatures at either side of that beam.

One general weak point we noticed was at the taping of window frames. In every case, there were tiny leaks at the interior corners in the frames where the tape had not been pushed tight into the those corners. We went round the entire house and sealed those little gaps.

In the end we achieved a rating of .59 air changes per hour, just under the requirement. According to Chris, drywalling and trim will continue to increase our airtightness. Keith Kauffman, the construction superintendant, takes this personally and you can be sure that all finish carpenters will have caulking guns in their pockets as they install the trim at each exterior opening. The official blower door test will be performed when the building is completed.

Here are some more of the thermal images: See the scale at right to find temperature/color calibration. Here you see an un-taped SIP panel joint. The wispy lines of color in the corner indicate air movement there.

Above you can see a a wall penetration that didn’t get fully caulked.

And here is Chris, explaining how it all works in three short segments.