Best economical way to seal a tongue & groove ceiling with rigid foam
Jayne_l
| Posted in Energy Efficiency and Durability on
My son’s house has the notoriously leaky tongue & groove ceiling with fiberglass batt insulation. Our plan is to pull up the fiberglass batts and foam seal in rigid foam between the joists. Because finances are an issue, we will probably do it in steps and have to re-use the fiberglass over top. Then when it is complete, we will add blown in cellulose on top.
What would be the minimum thickness and best type of rigid foam to use for this?
When re-using the fiberglass, do we leave the paper facing on, or should it be removed?
Is this a sound plan? Any suggestions are welcome.
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Replies
Jayne,
Please provide more details,.
1. Is this a sloped cathedral ceiling or a flat ceiling with an unconditioned attic above?
2. Please clarify how many layers you plan in your sandwich. It sounds like you are planning, from the bottom up: new ceiling, rigid foam, recycled fiberglass batts, and cellulose. Is that the plan? If so, it's unnecessarily complicated.
Sounds like attic access to fiberglass. The Kraft is not going to be a problem IMO. Keep it or lose it. Your project should work out well. One thing I know, spraying in the rigid foam is going to use lots and lots of cans of foam but not much you can do about that since you are doing a bit at a time.
Jayne,
As long as you achieve a relatively good air seal around the rigid foam boards between the joists your plan should have substantial benefits. I would suggest at least 1" thick foam. Thicker is better especially in heating climates but depends on your budget. Try to at least exceed local codes for ceiling R value by ~30%. I would recommend polyiso rigid foam and make sure. if it has one, the foil face faces down if you are in a predominately heating climate. I would recommend against using XPS because of its contribution to global warming potential due to their blowing agents.
You can replace the batts with the Kraft paper face down. Coming in later and blowing over loose fill will improve the overall thermal performance of the package with a reasonable price tag.
Yes we are in a heating climate (NW Pennsylvania 5a)
1.This is actually an A frame cathedral ceiling that the top portion (horizontal line of the A) is a flat ceiling that is open above to an unconditioned attic above. (excuse if i don't use proper building terms).
a. We will address the side unvented ceiling portion later which I know will involve layering inward with a new ceiling,but we are starting with the easiest and cheapest areas first.
2.A new ceiling is not in the budget, so I was thinking just one layer of rigid foam for air and vapor barrier next to the leaky tongue and groove. There is plenty of room above to blow in a lot of cellulose over the old batts, which would give them the most bang for the buck. I know it is complicated, but the money is tight and it is something we can do ourselves. But I am open to ideas if you have a better plan.
It is surprisingly easy to remove and re-install tongue and groove ceilings. (I've done it, typically the nails stay in the rafters and you just pull the boards off leaving the tongues intact and bend the nails over as you go). If I were you I would carefully pull the ceiling down, install taped foil-faced poly-iso foam to the bottom of the rafters foil side down, strip it with 1x3s and re-install the ceiling. you won't have to handle the fiberglass. you probably won't even have to re-paint the ceiling.