Retrofit attic/ceiling vapor barrier
Once again I need help from the pros. Please remind me to say no to these projects and explain to my friends and relatives that woodworkers don’t know building just because we share a few tools! Oh well, this nice lady does make good apple pie.
I’m upgrading the insulation in an attic that doesn’t have a good vapor barrier to the living space. It is a flat ceiling (not cathedral), and has open 2×6 joists (no attic floor) with only a few inches of fiberglass batts. After finding and sealing all the holes and leaks in the ceiling, wall sills, etc. I plan to either lay more batts to the top of the joists or get loose-fill blown in (with baffles to avoid covering the soffit vents). There’s some recessed lighting which I’ll check for I.C. rating, or build a box around (I saw this in F.H.).
Over most of the ceiling, the paper side of the batts was not well secured to the joists and has largely come away, or had been torn away, perhaps from homeowner DYI or recently installed A/C ductwork. Also, during an bathroom remodel, the batts were just laid into the joist cavities from above after the dryall ceiling was replaced.
I absolutely do not want to tear off the ceiling drywall thoughout the whole house. Can anyone suggest alternatives? My naive mind thinks of plastic sheeting installed somehow from above, or one of the rigid foam boards cut to fit and “glued” with that spray foam in a can.
Thanks a lot.
– Mark
Replies
That's easy enough. Blow in several inches of cellulose, (the ducts are insulated and sealed, right? If not, we should be talking about foaming the roof and bringing the attic into the living space) and use a VB paint on the ceiling. You've already taken the more important step of air sealing.
Andy Engel
Senior editor, Fine Woodworking magazine
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None of this matters in geological time.
Generally speaking, you don't need a vapor barrier in the ceiling. The moisture is allowed to travel up into the attic and be vented out. Also, the kraft facing is a moisture barrier and putting in two vapor barriers can trap moisture.
You get out of life what you put into it......minus taxes.
Marv
I agree with Andy and Marv, but would add that the current best practice is that while an air barrier is a necessity, a moisture barrier is not, in fact wall and ceiling assemblies should be somewhat moisture permeable to allow controlled moisture to pass and/or assemblies to dry. The vapor barrier paint Andy refers to is more akin to a lower permeability coating than a barrier.
My $0.02
Thank you all for your help. I'll happily paint the ceiling (it needs it anyway). After a few summary paragraphs I have a ventilation question.
The A/C duct work is insulated. The bathroom fan duct and all of the ceiling seals (A/C vents and bathroom fan) needs work. I recently read a procedure in F.H. on the bathroom fan/duct which I'll follow. The attic access pull-down stairs will get a box/cover.
It turns out the two recessed lights are not I.C and I will replace them. I had thought about building a box around the non-IC lights, but a little looking told me that was a no-no (FH 138?). Just one of many so-so items this lady got in her remodel.
It looks like most of my effort will be finding/sealing all the holes (I've found about a dozen already), the soffit baffles, and finding a pro for the loose-fill blow in.
If I may impose on you all for one more item. The attic venting looks well short of that normally recommended. There are two small soffit vents (about 6"x16") on each side of the house (total of four) and a temperature triggered exhaust fan on the roof (no ridge vent). I'm guessing it would be easier to change this now before filling the attic with more insulation, especially loose-fill. The attic is about 1500 sq ft (30' x 50'). I could do a continuous soffit vent and get a pro in to do a ridge vent. I've noticed some debate on the pros and cons of attic ventalation. Any suggestions?
Thanks again for all your help.
- Mark
Not sure how to tell if you're getting enough circulation but......check the roofing nails that are poking through the roof. If they are rusted, that means you need more air flow. The water coming up from the house is condensing on nails and will eventually rust them away.You get out of life what you put into it......minus taxes.
Marv
Since there is an AC system I'm assuming that you have a fair number of cooling days, in which the warm moist air outside wants to condense closer to the living space, so perhaps the moisture barrier isn't a great idea. Local building codes will probably reflect the best advice on that. Back home in Wyoming (7,000 ft. and cool temps) we always use a moisture barrier in the walls and ceiling, while here in Idaho (3,200 ft. and warm temps) walls yes, ceiling no.
Rigid insulation foamed at corners is a barrier that works in any climate, as are a few inches of professionally-applied spray foam.