Is 4.5 ACH50 too high?
Bought a new home, fairly new construction (2yrs old) 3400 sq ft. 2 levels. our area straddles zones 5b and 6b, so depends on the year, can be either pretty cold or mild winters. summers are always dry.
after our first heating/cooling season, with pretty high utility bills (gas heat ~$300/mo in winter, summer electric cooling bills even higher), we got an energy audit. We were already experiencing hot/cold rooms, so guessed there was likely an issue. auditor was not impressed wtih attic insulation (batts b/w joists and topped off wtih blown in. supposed R49, but he suspects it’s not performing to that level due to all the batts on the attic floor). Camera showed some gaps in the wall batts at the top plate, corners. Crawlspace wasnt too bad. currently has dirt floor with plastic barrier and batts b/w joists. Blower door = 4.5 ACH50. HVAC air balance looked good
Obviously, with everything being finished, there’s only so much we can do for air sealing. Both the energy auditor and insualtion folks recommend sealing up the crawlpace to reduce stack effect. I’ve got 2 estimates, one for 6ml + 2″closed cell on walls (poured conrete), and 12mil +3″ closed cell. the latter is almost twice as much. Is it twice as good?
They are willing to go, take all the attic insulation out, air seal attic floor (that can be reached) with foam, but it’s very expensive. Insulation guy doesn’t think it will be worth the cost (i may not see a big change in blower door result or comfort). we have tried to seal registers, can light fixtures, outlets, etc, best we can, still 4.5ACH. we do have a fireplace andrange hood venting outside. not sure if that makes a difference.
My impression is we get lots of leakage into the/from the attic (the hatch was not well sealed, and we’re going to fix that). We get lots of ice dams, and the snow on our roof is always gone before everyone else’s in the area (accounting for roof color and house orientation, etc). I’m not sure if just sealing the crawlspace will make a significant enough difference?
Any thoughts/advice? thanks in advance!
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Replies
To answer your title question, yes. The IRC has required 3ACH50 for your zone since the 2012 revisions. That's the code minimum that every builder, even the cheap ones, is supposed to hit.
--John
Unfortunately, not every jurisdiction has adopted the 2012 (or 2015) code. For a new house, 4.5ACH50 is pretty lousy, code required or not.
As for the fix in the attic, it shouldn't be necessary to air seal the entire attic floor with foam, except to fill whatever holes there are (electrical or plumbing penetrations and ?) and then reinstall the batts and/or cellulose.
The fireplace could be a major culprit.
The "and?" in Stephen's post would include all top plates of interior walls.
Yes, 4.5 ach50 is too high. The fact that you have no snow on your roof and ice dams is totally unacceptable. So, yes, it's a good idea to fix these problems.
It's often a good idea to have a blower door operating, depressurizing the house, as you are looking for air leaks and sealing them. The work is called "blower-door-directed air sealing." The workers should concentrate in the crawl space and attic.
In most cases, it's best to hire an experienced weatherization crew (or home performance contractor) for this work -- a contractor who has heard of the term "blower-door-directed air sealing" -- rather than a spray foam contractor.
-- Martin Holladay
Thanks everyone for the answers. Unfortunately, very few builders in our area build to tight envelope standards, so numbers like this are kind of common (so I hear). A lot of builders are starting to offer HERS scores (ours was 60), but clearly there are components of that, that have room for improvement.
I will look around to see if there are any contractors that do blower door directed air sealing. I know a few do pre and post, but I don't think they are testing WHILE sealing. My concern with the attic space, some parts are inaccessible. with our luck, that's where the big leaks will be :-) I think a big part of the cost I was qouted was just to get the insulation out/labor. I'd hate to pay all that, and not get mouch benefit, so I may start in the crawl, as I know they can get in there and do a good job. thanks
You should have been able to determine whether the fireplace was a major air leakage offender during the blower door test. It's clearly a prime-suspect. If it's a pre-fabbed sheet metal unit built into a chase, very often the chases are poorly air sealed and often poorly insulated as well, even if the fireplace unit itself isn't a leaky sieve (though they often are.)
Air & heat leaks into the attic sufficient to melt all the snow and form ice dams with an R40+ insulation on the attic floor are likely to be wetting the insulation in some places, and driving air infiltration high enough to make for overly-dry wintertime conditioned space air. Even if there isn't "payback" for air sealing on an energy-cost basis, there's usually immediate payback to getting it under 3ACH/50 on a comfort basis. (With diminishing returns below that level.)
The payback might be in not needing to re-roof as soon and not reading to repair water damage from ice dams and moisture damage from interior air bringing moisture into the attic.
Good points. and now that I think about it, I do remember while the blower door was going, there was quite the draft at the fireplace (it is a prefab metal one). thanks again