Airtighness Goals
I think that we should raise or SET the bar for air tightness goals.
What is the bar? Is there an Energy Star standard?A LEED standard?
Should it be the Building America Westford Metric?
What is the Westford metric? is it 1.5 Air changes per Hour at 50p or is it 3 ACH @ 50?
How about Passivhaus Standards? 0.6 ACH50
How many out there are surpassing the Westford Metric?
Is any one besides Passive House USA meeting Passive house airtightness standards?
What is your best blower door result and how did you achieve your air barrier?
Asked by John Brooks
Posted Sat, 04/25/2009 - 10:06
Posted Sat, 04/25/2009 - 10:06
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John
Our last house tested at 0.7 ACH50. We had 8" of open cell in the roof, 6" JM Spider in the walls, moderately well detailed Tyvek (missed the FEMA header-wrap detail on this one) and caulked bottom plate and routine E-star thermal bypass checklist details.
Our 110 cfm bath fans on time delay motion sensors were only pulling 70 CFM even with well detailed metal duct. We had a sealed crawl with a bath fan pulling another 70 CFM 24/7 through the chimney to the roof.
I'd vote for setting the bar at 1.5 ACH50 provided it is accompanied with a 7.5 CFM/occupant fresh air strategy.
Posted Fri, 05/15/2009 - 23:33
Michael,
That is an impressive ACH (almost Passivhaus)
I think that ALL new homes(not just extra tight) should have a calculated fresh air strategy.
Leakage is not a reliable Fresh Air Strategy.
That also means that we MUST measure the ventilation airflow as you have done.
I agree that 1.5 ACH50 is a respectable and achievable goal for all houses.
I also think that it will be very difficult for most builders to achieve "1.5" with air tight drywall strategy alone. Just consider the Building America Westford House.
Air tight Drywall seems like a good idea .. but it is aparently Not So User Friendly.
I think the airtightness of my house(1.4 ACH50) is mostly due to the combination of 100% structural sheathing, open cell spray foam and careful sealing between framing to framing and framing to concrete.
If I had been more aware of Passivhaus at the time..than I would have put more effort into Airtightness and set my goal to be 0.6 ACH or better.
Besides Passive House USA and Thorsten Chlupp in Alaska .. I have not seen any published USA Airchange results that would meet minimum PHouse standards.(you got close)
Thorsten's results are likely due to the fact that he does predrywall blower door testing and corrections.
according to Thorsten's recent JLC article
"If you hold off doing the blower-door test until the insulation and drywall are installed, it’ll be too late."
This strategy means that Air tight drywall aproach is not an option.
Air leakage is not just an Energy factor ... it is a Significant durabilty Issue.
http://www.passivhaustagung.de/Passive_House_E/airtightness_06.html
Michael.. I understand your air barrier at the roof... but I am not clear about your walls.
Did you use 100% structural sheathing?
Do you test before drywall?
Can you 'splain Fema Header wrap? I am not familiar
Posted Sat, 05/16/2009 - 10:12