We got a remodel going in a new town, and yesterday we got spanked by a BI in a town we haven’t worked in yet on a vapor barrier inspection.
This is a one hundred year old house, and we are gutting the lower floor and leaving the second floor plaster walls and ceiling intact. We firred the lower 2×4 walls out to accomodate a R-21 Batt and added a a a 4 mil poly VB. The VB was caulked to top and bottom plates and seams taped.
He was over-the-top on the VB inspection. Had us go back and tape even errant staple holes. Inspected every bead of caulk and if there was one spot where there was a 1/8″ gap in the coverage we fixed it. He got done with all this and asked if we were gutting the upstairs. Duh! I think a light MAY have gone on in his engineer’s brain that it might not make a lot of sense to be taping a staple hole on the first floor when the upstairs doesn’t even have a vapor barrier.
Anyway, I plan to call him and very politely ask him to cite me the code that tells us that we have to take a vapor barrier to this extreme on a house that is about 50% gutted. Anyone know anything about this. I believe it would be in the Minnesota State Energy Code. All can find pertains to new dwellings.
Replies
Marson,
Everything you will ever need to know about vapor barriers (also vapor retarders, there's a difference), you can find on BuildingScience.com:
http://www.buildingscience.com/documents/reports/rr-0410-vapor-barriers-and-wall-design
will get you started.
But the inspector wasn't being too crazy checking all the holes, a hell of a lot more moisture can get into the wall through a small hole than will diffuse through the wall materials themselves.
Thanks for the reply. I am well aware of the science of vapor barriers. I'm looking for a code citation as it pertains to a house that is only 50% gutted.Remember, this is a house that has stood for one hundred years without any vapor barrier, with blown cellulose in the walls since probably the 70's.I intend to call the inspector next week and ask for such a citation. If he is asking me to spend an extra say $500 on what I view as overkill given the circumstances, I'd like some back up.
Ah, sorry can't help you with local code stuff. But if code doesn't agree with these articles, i've heard that generally if you present all this science to the inspector (politely), they generally shut their mouths and go away... Like you said, house has been standing for 100 years, no VB, but also no insul to create condensing surfaces, either...
Well, if we are going to talk about building science, we should have some observations, no? I just counted and my company has gutted or partially gutted 13 houses in the last year. All were on either side of 100 years old. 7 of them had blown cellulose, 2 had old style fiberglass (probably from a remodel in the 50's) and 4 weren't insulated at all. NONE , I repeat, NONE of these had any evidence of condensation in the walls. (some had obvious roof issues that led to rot). So the idea that if you don't tape up a staple hole will lead to condensation in the walls is balderdash. I think what saves these old houses is breathable sheathing.
When you add a partial vapor barrier and stuff the cavity with insulation, you slow down air migration to the point where it could condense on the insulation, leading to mold and all that. Without a barrier, even with (leaky) insulation like FG or loosely blown cellulose, there was probably enough air movement to carry the moist air outdoors and keep condensation from occurring. Poly + FG is probably the most susceptible combination for mold.
I have not gutted some thing in a couple of years, but I believe our city does not require a vapor barrier for walls any more, just crawl space. I will have to call and check to be sure, but from the attachment which is based on the IRC it does not call out for one.
Wallyo
Did you use kraft-faced batts? If so, it looks like your best bet would be to just remove the poly. Leaky poly will trap moisture. Kraft appears to be sufficient for your application and will allow some breathing.
Could you tell him you are going to use vapor barrier primer/paint? I've never used it myself.. but starting to think about going that route.