Blower Door - Slight Disappointment

Ok, we had what was supposed to be the second and LAST blower door test, but I am not happy with the result and I may have Dean Benton of Benton Green Energy come again after I have fixed some problems. 

Blower door reading on August 6, 2014

You may recall that a blower door test helps determine how much air leakage you have through the building envelope. The test involves putting a fan in an outside door frame and depressurizing the home to accentuate the air leaks. The house is depressurized to a level of 50 pascals which is about equivalent to the force of a 20 mph wind on the home. There are 2 main values that you get from the test - one is directly from the manometer as shown above and one is calculated based on the volume of the house. This article, Blower Door Basics by Martin Holladay on Green Building Advisor (GBA) explains it much better than I ever could.

Blower Door Set-up while we were at the rough-in stage. 

The number shown on the manometer above is called cfm50 or the amount of air that moves through the home at 50 pascals of pressure. The other number is ach50 or air changes per hour at 50 pascals.

Our previous reading was 98 cfm 50. The above reading is 235, but I think it leveled out at 220. In any case, the number has more than doubled - 2.4 times greater than the last blower door.

What happened??

Well, I have some ideas.

What do you think about this dryer vent? Do you think that there is some leakage around this pipe?

Dryer vent through the wall, not sealed around the vent pipe. This was installed AFTER the first blower door test.

What about the vent cover for the kitchen fan? Do you think that those little plastic louvers seal out air?

This flimsy plastic piece covers one of the fan vents. A similar cover was on the dryer vent. 

Now the photo below may show a less important air leak. This is the inside view of the Lunos e2 - a heat recovery ventilator (HRV) that exchanges outside air for inside air. It does go through the wall in large tube. We did seal the tube to the sheathing inside and out before the walls were closed in. Still it is designed to move air through the home. You may wonder why we go through all the trouble to seal up every possible hole in the building envelope and then deliberately install a fan to exchange air. Well, when you have a very well air sealed home, you need to move more fresh air through for the inhabitants, but it needs to be filtered, conditioned air, not random leaks. That's what the HRV provides.

Lunos e2 Heat Recovery Ventilator (HRV)

The reason I did not calculate the ach50 is because I am confused about the volume of the house. The house is a Cape Cod design with kneewalls and sloped ceiling upstairs so I don't really know what counts as the house or not.

For example, the space above the bathroom and the bedrooms is not really sealed off from the rest of the house. It is within the thermal envelope of the building. Do I count that? I think so, but I am not sure. I am going to post a questions on Green Building Advisor to get their advice.

Area above the bathroom. You can see the Intello Plus smart vapor retarder from 475 High Performance Building Supply. The ceiling joists are insulated with dense pack cellulose. There will be a small door that fits in the opening. It does not set tightly to the frame, however. Is this within the thermal envelope?

So, the big change from the rough-in stage to almost completion (I know, almost completed at 18 mos later - crazy ) is the vents. We taped cardboard over the area where the vents were during the first test, but I don't know if you tape over vent covers when you go for the final test. That's another question for the knowledgable people at GBA.

I'll let you know more later. Thank you for visiting here. 

Insulation in Kneewalls

Kneewalls are a challenging part of a home because they are a little bit hard to build and insulate. We chose kneewalls because of the expanded space and better, though challenging, insulation.

Here is a drawing from Shelter Kit showing the kneewall extension. So rather than having the rafters meet the floor joists directly, there is a extension of the wall that supports the rafters. This gives you more usable space.

Shelter Kit - Drawing of Kneewall 

The next drawing shows the increase in space in the upstairs with kneewalls.

Comparison of space with and without kneewalls

The difficulty arises with the funky cavities made by these kneewalls. How do you insulate this space?

Dormer framing with wall framing behind it

I posted a question on Green Building Advisor about it because I just didn't think the insulation company would be able to blow-in cellulose effectively in these spots. I decided to fill them with Roxul mineral wool insulation and then I'll cover that with the Intello Plus smart vapor barrier. Then we will insulate with the cellulose over that. Does that seem like a lot of insulation for this area? Well, it is, but this is what I call "a vulnerable area" a seam between sections of the house (the roof, the wall and the rim joist below) that is very prone to air leakage. 

Also the details of adding exterior insulation to this short section of wall would have been very challenging. So we omitted it from this section of wall. And we built this wall before I started going crazy about air sealing so the inside of this cavity is not air-sealed as almost every other cavity in the house is. The outside is taped though. 

Now you can see my efforts at insulating the kneewalls. This might not meet Grade 1 insulation standard, but the voids are filled. Remember that there will be at least 5 inches of cellulose interior to this insulation to make sure the wall is well insulated.

Intello Plus membrane will be stapled between the Roxul mineral wool insulation and the dormer wall framing in front. That space will be filled with dense-packed cellulose.

Bedroom kneewall stuffed with Roxul mineral wool insulation.