Can this really be? ACH50 of 0.62?
With homage to Martin’s Christmas poem, I thought I’d share the results of my blower door test and ask… Is this really to be believed?
The interior volume of my home, including unfinished basement, is 53,569 ft^3 as calculated in my SketchUp model of the place. The blower door test results showed 551 CFM at 50 pascals, giving an ACH50 of 0.62.
I set out this year to build a “pretty good house”, and I used this resource extensively in that quest. But, I’m no builder, and while I employed a great number of the methods and strategies I found at GBA and elsewhere to limit air leaks, I can’t say I did every one to perfection, or even completion. Here are some of the techniques I did use:
1. ICF poured concrete basement
2. Foam gasket and acoustical sealant under mud sill
3. Caulked perimeter of sole plate
4. Covered rim joist exterior with 1″ XPS panels, foamed in place
5. Great Stuff Door and Window seal around all doors and windows
6. Canned spray foam everything that I thought could be a path from outside to inside
7. And finally, insulated by applying ccSPF to exterior sheathing to create my “envelope”
I don’t really feel like I did anything all that special. No $30 rolls of european tape, or caulking OSB panels. No special windows. (I installed Anderson 400 series double hungs, and 200 series casements).
I believe the ccSPF applied to exterior sheathing deserves the credit. Here’s my question… are things likely to improve further, or worsen, once I actually install air-tight drywall, but then punch holes for HRV, dryer vent, bath exhaust fans, and range hood?
I got so excited about the results that I am now motivated to try to get to Passivhaus target ot 0.60. I’ve already identified a few “weak” spots with the IR camera, and I had my plumbing stack open to the atmosphere during the test, so there’s hope… right?
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How big is your house? Assuming you have 8 foot ceilings in the basement and 9 foot on the single main floor above a full basement suggests about 3150 sq ft or a rectangle that is 36 feet by 87.5 feet.
Kent,
Congratulations on your blower door results. If you re-test later, your results could be better or worse -- depending on your attention to details. Good luck.
Jerrry - Directly answering your question, my house's "footprint" is a bit over 2000 sq. ft., basement ceiling height 9', main floor ceiling 9', and 2nd floor 8'. Just taking floor area times ceiling height gives me a "usable living space volume" of 47,000 cu ft, but neglects other interior conditioned space volumes, such as open-web truss volume and "storage" space behind knee walls.
Your question gets to the heart of what constitutes "interior volume", however. Is all space inside the thermal envelope included in the blower door calculations? Or just usable living space? XRG Concepts, who performed the blower door test, asked for total interior volume within the air barrier, which seemed to make sense to me (.... wait.... do I get to include space within double stud wall cavity interior to the ccSPF?!?)
Anyhow, I was, honestly, astonished that the results came in this well. I was targetting an ACH50 of under 1.0, and I believed that the ccSPF would be the key component in the design that would get me there. I'd be very interested in the experiences of others, especially anyone else who employed spray foam as their chief air-barrier layer.
Kent, Well done! It offers encouragement for the rest of us. No real benefit to making that last jump to .60, but probably worth doing just for the fun of it.
Before you go any further, just be aware that Passive House calculates volume differently - subtracting the volume of interior walls most significantly.
Kent, in the highly unlikely event that your technician accidentally had Ring A installed on the fan, but had the manometer set for Ring B (as shown in your photo), the actual flow would have been in the range of 1660 CFM50. You seem surprised that your test result was as low as it was, so I raise this as a possibility to consider. It is highly unlikely that this happened, and it is highly likely that you got an accurate test... however... I will admit to mishandling my gear on at least one occasion and getting what seemed like a remarkably good result on a test. When I rechecked everything, I found my error. It is also possible to get inaccurate readings with things like pinched hoses or even a manometer that is needing calibration.
Again... I doubt it happened, and I think your result is right... but there are ways to get a bad number, and I've done it.