ASHRAE Journal - May 2011 - 66

building sciences

Photo 10 (left): Bedroom Over Garage. Unfortunately, in my experience, garages are not effectively isolated from houses, especially at the second floor assembly to interior garage perimeter. Photo 11 (right): Bedroom Over Garage Done Well. Notice how beautifully the floor joists are draftstopped over the top of the wall that separates the interior garage perimeter from the house. This location typically represents a huge leakage area (aka, big holes). The true believers are a fun, well-meaning bunch, and I tend to get along with them. I invite them to my parties, but I have yet to be invited to one of theirs. Apparently, there is a message there. It could be my personality. On our custom home stuff we get to 1.5 ach@50, but it is a lot of work. The group that really has me confused are the PassivHaus folks who are pushing 0.6 ach@50Pa. Yes, that is the number. It comes from Germany, so it must be right. Have you any idea how difficult it is to get to 0.6 ach@50 Pa? The number doesn’t seem to be based on anything that makes any sense. It is less than half the R-2000 number that didn’t make any sense. What I have been more or less able to figure out is that the 0.6 ach@50 Pa doesn’t come from any energy conservation rationale directly; it seems to be based on the need to prevent moisture problems in highly insulated building enclosures. That is the argument for the number 0.6 ach@50 Pa as I understand it. Never mind that that the number, in itself, makes no sense as you can easily design highly insulated building closures without moisture problems that are not anywhere that tight. So why should I care? Or why should we care? From my own personal perspective you should be able to pick any number you want. And hats off to the PassivHaus folks for their own personal program number. It is their program, and they get to do what they want as far as I am concerned. I only get irritated when they criticize everyone else. This big old mangy junkyard dog of an engineer tends to bark back when criticized, and I bark back even louder when my friends get criticized, especially on stuff that is arbitrary and capricious. And arbitrary and capricious is OK too—in your own personal program and your own personal life—but not in mine. Public policy and national standards should not be arbitrary and capricious. That brings us back to the beginning more or less. Big holes, blower doors, tightness limits, ventilation, ventilation rates, combustion safety and public policy as opposed to private policy.
66 ASHRAE Journal

So, from a public policy and national standard perspective, in my opinion, get rid of the big holes, provide a ventilation system and ensure combustion safety and call it a day. Getting rid of the big holes means less than 3 ach@50 Pa as measured with a blower door. That is what a blower door is good for. Don’t use a blower door to assess acceptable indoor air quality because the approach is not reliable. What is the best way of providing acceptable indoor air quality and ensuring combustion safety? Easy. Install a controlled ventilation system. Start with ASHRAE Standard 62.2 recommended rates and add some slack and then turn things down and give control and responsibility to the folks in the house. Install sealed combustion or power vented appliances. Let me repeat that last part: install sealed combustion or power vented appliances. What is the next best way? Follow the combustion safety provisions of the building codes—they have it right—but installing sealed combustion or power vented appliances is even better. And don’t forget about this controlled ventilation thing. What is the worst way? Tightening up a house to an arbitrary and capricious value established just for the purpose of avoiding having to install a ventilation system and avoiding having to meet the combustion safety provisions of the building code, but making it look technically sound because a geek with a blower door did a test. Apparently, there is a lot of money in testing, but not so much in fixing the actual problem. What is the next worst way? Tightening up a house to an arbitrary and capricious value that is almost impossible to achieve and then overventilating it. If I had a choice, between these two, I would choose the latter, of course. But what a choice. I think, maybe, Goldilocks had it right, not too leaky, not too tight, just right. Then, add controlled ventilation, but not too much, not too little, just right. And, of course, sealed combustion and power vented all around. Joseph W. Lstiburek, Ph.D., P.Eng., is a principal of Building Science Corporation in Somerville, Mass. Visit www. buildingscience.com.
ashrae.org May 2011



ASHRAE Journal - May 2011

Table of Contents for the Digital Edition of ASHRAE Journal - May 2011

ASHRAE Journal - May 2011
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Seismic Restraint
Plug Load Design Factors
Technology Award Case Studies:
State-of-Art School
Green School Lab
Eco-Friendly, Affordable, School
Building Sciences
Special Section
InfoCenter
Solar NZEB Project
Emerging Technologies
IAQ Applications
Washington Report
International Column
Products
People
Classified Advertising
Advertisers Index
ASHRAE Journal - May 2011 - Intro
ASHRAE Journal - May 2011 - ASHRAE Journal - May 2011
ASHRAE Journal - May 2011 - Cover2
ASHRAE Journal - May 2011 - 1
ASHRAE Journal - May 2011 - 2
ASHRAE Journal - May 2011 - Contents
ASHRAE Journal - May 2011 - Commentary
ASHRAE Journal - May 2011 - 5
ASHRAE Journal - May 2011 - Industry News
ASHRAE Journal - May 2011 - 7
ASHRAE Journal - May 2011 - 8
ASHRAE Journal - May 2011 - 9
ASHRAE Journal - May 2011 - 10
ASHRAE Journal - May 2011 - 11
ASHRAE Journal - May 2011 - 12
ASHRAE Journal - May 2011 - 13
ASHRAE Journal - May 2011 - Letters
ASHRAE Journal - May 2011 - 15
ASHRAE Journal - May 2011 - 16
ASHRAE Journal - May 2011 - 16a
ASHRAE Journal - May 2011 - 16b
ASHRAE Journal - May 2011 - 17
ASHRAE Journal - May 2011 - Meetings and Shows
ASHRAE Journal - May 2011 - 19
ASHRAE Journal - May 2011 - Seismic Restraint
ASHRAE Journal - May 2011 - 21
ASHRAE Journal - May 2011 - 22
ASHRAE Journal - May 2011 - 23
ASHRAE Journal - May 2011 - 24
ASHRAE Journal - May 2011 - 25
ASHRAE Journal - May 2011 - 26
ASHRAE Journal - May 2011 - 27
ASHRAE Journal - May 2011 - 28
ASHRAE Journal - May 2011 - 29
ASHRAE Journal - May 2011 - Plug Load Design Factors
ASHRAE Journal - May 2011 - 31
ASHRAE Journal - May 2011 - 32
ASHRAE Journal - May 2011 - 33
ASHRAE Journal - May 2011 - 34
ASHRAE Journal - May 2011 - 35
ASHRAE Journal - May 2011 - State-of-Art School
ASHRAE Journal - May 2011 - 37
ASHRAE Journal - May 2011 - 38
ASHRAE Journal - May 2011 - 39
ASHRAE Journal - May 2011 - 40
ASHRAE Journal - May 2011 - 41
ASHRAE Journal - May 2011 - 42
ASHRAE Journal - May 2011 - 43
ASHRAE Journal - May 2011 - Green School Lab
ASHRAE Journal - May 2011 - 45
ASHRAE Journal - May 2011 - 46
ASHRAE Journal - May 2011 - 47
ASHRAE Journal - May 2011 - 48
ASHRAE Journal - May 2011 - 49
ASHRAE Journal - May 2011 - 50
ASHRAE Journal - May 2011 - 51
ASHRAE Journal - May 2011 - Eco-Friendly, Affordable, School
ASHRAE Journal - May 2011 - 53
ASHRAE Journal - May 2011 - 54
ASHRAE Journal - May 2011 - 55
ASHRAE Journal - May 2011 - 56
ASHRAE Journal - May 2011 - 57
ASHRAE Journal - May 2011 - Building Sciences
ASHRAE Journal - May 2011 - 59
ASHRAE Journal - May 2011 - 60
ASHRAE Journal - May 2011 - 61
ASHRAE Journal - May 2011 - 62
ASHRAE Journal - May 2011 - 63
ASHRAE Journal - May 2011 - 64
ASHRAE Journal - May 2011 - 65
ASHRAE Journal - May 2011 - 66
ASHRAE Journal - May 2011 - 67
ASHRAE Journal - May 2011 - InfoCenter
ASHRAE Journal - May 2011 - 69
ASHRAE Journal - May 2011 - 70
ASHRAE Journal - May 2011 - 71
ASHRAE Journal - May 2011 - 72
ASHRAE Journal - May 2011 - 73
ASHRAE Journal - May 2011 - 74
ASHRAE Journal - May 2011 - 75
ASHRAE Journal - May 2011 - 76
ASHRAE Journal - May 2011 - 77
ASHRAE Journal - May 2011 - Solar NZEB Project
ASHRAE Journal - May 2011 - 79
ASHRAE Journal - May 2011 - 80
ASHRAE Journal - May 2011 - 81
ASHRAE Journal - May 2011 - 82
ASHRAE Journal - May 2011 - 83
ASHRAE Journal - May 2011 - 84
ASHRAE Journal - May 2011 - 85
ASHRAE Journal - May 2011 - 86
ASHRAE Journal - May 2011 - 87
ASHRAE Journal - May 2011 - 88
ASHRAE Journal - May 2011 - 89
ASHRAE Journal - May 2011 - Emerging Technologies
ASHRAE Journal - May 2011 - 91
ASHRAE Journal - May 2011 - 92
ASHRAE Journal - May 2011 - 93
ASHRAE Journal - May 2011 - 94
ASHRAE Journal - May 2011 - 95
ASHRAE Journal - May 2011 - IAQ Applications
ASHRAE Journal - May 2011 - 97
ASHRAE Journal - May 2011 - 98
ASHRAE Journal - May 2011 - 99
ASHRAE Journal - May 2011 - 100
ASHRAE Journal - May 2011 - 101
ASHRAE Journal - May 2011 - Washington Report
ASHRAE Journal - May 2011 - 103
ASHRAE Journal - May 2011 - International Column
ASHRAE Journal - May 2011 - 105
ASHRAE Journal - May 2011 - 106
ASHRAE Journal - May 2011 - Products
ASHRAE Journal - May 2011 - 108
ASHRAE Journal - May 2011 - People
ASHRAE Journal - May 2011 - Classified Advertising
ASHRAE Journal - May 2011 - 111
ASHRAE Journal - May 2011 - Advertisers Index
ASHRAE Journal - May 2011 - Cover3
ASHRAE Journal - May 2011 - Cover4
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