Can you get a house any tighter?

[davenorthup]

Going to do some finish work on a house in the bush. The owners just sent a note with their blower door test results of:

0.1 ACH at 50.0 Pa

The house is small - about 16 x 20 with a loft. It has 2 windows, one door. Basically has an outer and inner shell separated with about 30" of 'blown in' for the walls. The ceiling insulation is well over R-100...

Very impressive to say the least - anyone heard of such a tight house?

[Bluewoodrock]

0.1 ACH at 50.0 Pa

You sure that's not a corrected ACHn number? I've heard of buildings that tight at natural air changes- not at 50 Pa. Not to say it's not possible, but people get these results confused all the time.

[ThingOfBeauty]

A couple of friends built a PERSIST style guest house here, also about 16 x 20, though it had nice 12' walls and cathedral ceiling.
They couldn't get the blower door to give a reading even on the small ring.
They were so excited they were at the time talking about going back with a duct blaster to see if they could get numbers that way!
2x4 walls, taped tyvek, two layers of 1 or 1.5" XPS taped both layers, over the roof with the same stuff.

[worthy]

It would be just as interesting to see a reading on the air quality of such a dwelling. I can't help but recall the deaths of enthusiastic "sealers" when the energy savings mania first hit in the '80s and they sealed up their homes on the model of a plastic bag wrapped around your head.

******
I built a custom house a few years ago that I figured was pretty tight. Lots of foam and gaskets. I suggested the owners might want an HRV. It wasn't required by Code so they said, "No."

[davenorthup]

Mike - yep it was definitely at 50 Pa.

Doug - I wondered how they got that reading as well. On my own house years ago we ran into the same problem; due to the smaller size of the structure. I think the rater opened a window to get it started (I forget)- I am not sure how they got the reading...

Worthy - they have an HRV. You are right you can not seal these places up w/o dealing with fresh air. I heard awhile back that code (might just be local code) was catching up and if you had an "unusually tight house" code would required an HRV for new construction. Unusually tight = vapor barrier.

On the flip side I saw a rating 2 weeks ago that had 32 ACH - granted there was no insulation yet; it was an old house and likely has been that leaky since the 50's...

[Alaskan Son]

.10ACH @ 50Pa? Crazy!!!

I built a small, simple duplex last summer with .10 ACH natural infiltration. It was 2 ACH @ 50Pa. We left the energy raters manometer hooked up and turned the kitchen and bath fans on and quickly got the house up to like 80Pa I think it was. Not so good. We installed some Fresh 100s and there were also some crawlspace air inlets that were normally open, but I seriously think if its tight it needs an HRV, if no HRV leave it leaky. I built my own house to the new ventilation standards we have here without an HRV and my energy bills are actually higher now than the were in the last house I built (comparatively leaky without any real ventilation standards).

FYI while we're on this subject, something to think about for those of you who live in snowy areas. Switching from naturally aspirated boilers and furnaces in the garage to sealed combustion...
I didn't realize until I i did this in my own home that the boiler or furnace also ventilates the garage and removes the moisture in the air. Now with my house being so tight and the boiler being so efficient, there's no way for the humidity (especially from the snow melting off our vehicles) to escape so all my garage windows start sweating like crazy. It could be addressed with a fan or something I know, but its just something to be aware of.

[David Meiland]

A 16x20 house with 8-foot ceilings (assumption) has 2560 cubic feet. Point-one of an air change would be 256 cubic feet of air. The blower door would have to move and accurately measure 4.27 CFM50. Not possible as far as I know (and I only have Ring C anyway) so I would probably have to send Ted in there to test that house at 500 pascals and break all the windows, or possibly cause a roofing failure.

It can't be done with a Minneapolis duct blaster either, they only go down to ~20 CFM I believe.

[Allan Edwards]

16' x 20'? That's not a house that is a master closet (her side only!).

[Ted S.]

I've never had the problem the house is so tight that it can't be measured. I guess that would be the case here.

Could it be any tighter? I don't know, I guess it could be theoretically 0ACH50. That's pretty scary as far as I am concerned.

Most of the folks who build these high performance homes know what they are doing, they know about ventilation and back drafting or are assisted by others who do.

What's really scary is that as these air sealing requirements get pushed into the mainstream, they become practiced by builders that have absolutely no idea about the science of it all. No offense to them, they have plenty of things to worry about and energy efficiency requirements are advancing very quickly.

The more houses we do, and the more jobs we stumble into as things are already progressing, the more I realize we are going to have some real problems out there.

I hope the ventilation requirements and combustion safety testing gets as much as attention as air sealing, it should be progressing as fast if not faster than the air sealing requirements. Air sealing right now is like a show off type thing, the tighter you are the bigger bad ass you are. Meanwhile the Jenn Air is over running the flue draft, and if you cook fish you're going to stink for a week.

[Ted S.]

16' x 20'? That's not a house that is a master closet (her side only!).

Or a Man Room, with a pool table, shag green carpet and a vintage wood clad console TV.

[dgbldr]

The house is small - about 16 x 20 ... about 30" of 'blown in' for the walls.

So is that 16x20 outside or inside ? :)

[Lavrans]

So is that 16x20 outside or inside ? :)

That's the same thing I thought...

[m beezo]

That's the same thing I thought...

16 x 20 on the inside would be different than 16 x 20 on the ouside if they have such thick walls that you are loosing over 4 ft of wall off the two sides. That would then be a 12 x 16 house on the inside. Wouldn't it?

[davenorthup]

It's a little bigger than that, but yeah those are the interior measurements. The whole thing totals out at about 600FT2.

I have not seen the place yet in person and Allan made me a little worried b/c my contract states I am working on a house and not a closet. I double checked - it's a house Allan, and you had me all worried for nothing. Who wants to spend 12 days working in a closet?

David - it has 2/3 loft above. So a little more cubic space than you figured. I do not operate blower doors so know little of their capacities. I do not remember the total ceiling height.

Michael - I think at 2 Pa one should likely have an HRV. I wonder why your tighter house is more expensive to heat than your previous all other things constant? We are essentially tripling the size of our house currently and my fuel usage will be about the same for the greater space. My electric will increase a little b/c of the HRV. My current house is very tight; but only has R-19 walls and R-38 roof and double pane windows. New complete house will have R40 walls and R60-80 ceiling, triple pane and be a REMOTE house...

Interesting observation RE the the garage moisture. Never thought about the ramifications of removing the ventilation ducts when switching to sealed combustion. No garage here. :)

I agree Ted - I have spent a good part of this spring doing repairs on homes with improper uses of vapor barriers, no air sealing, improper ventilation and so forth. We at least have a 2 day cold climate building class required before licensing; but we still see some many errors...

When I am there I'll post some more information and maybe some photos of the place if I get their permission. I have seen a lot of progress shots and the owners know what they are doing and doing a great job at the house construction. You have to be pretty sharp when every part of your project arrives by barge or plane.

[David Meiland]

it has 2/3 loft above. So a little more cubic space than you figured. I do not operate blower doors so know little of their capacities. I do not remember the total ceiling height.

Let's say it has another 50% volume over what I figured, with a full 12/12 cathedral ceiling. That would give it 3840 cubic feet. Using the E ring on the blower door gets you down to 8 CFM I think, so you'd be on the very edge of conducting a single point 50-pascal test. The fact that there are only two windows is probably the only reason I can think of for a test result that low, other than operator error or a manometer out of calibration.