Air-Sealing a Tongue-and-Groove Ceiling
Hi to all,
Long time reader of GBA and FHB. Quick abbreviated intro, (not sure if this the right place for it?) finish carpenter for 15 years, mostly custom cabs and trim work but I’ve been on my own for the last 5 working on all sorts of construction projects. Try to focus on kitchen install but I’ve done many basements, decks, siding etc.
My wife and I recently moved back to my hometown and purchased our first home together. We love the house but cosmetically its not entirely our style and are going to address updates in stages.
House is located in York, PA Zone 4a. It was built in 1978 by a local Chevrolet dealer owner. Its an all brick ranch (4300 sq ft total) with walk out basementand 2′ overhangs all around. 2×4 construction with 1 1/2″ foam board (looks like polyiso with some type of fiberglass facers. I think pretty novel in 1978) and r-13 fiberglass in the walls. Gas boiler with baseboard radiant heaters and 2 separate traditional ducted ac units.
I know I’m going to have a 100 other performance questions down the road but 1 of my first projects is to update the great room and I have some questions how to handle the cathedral ceiling. Currently the existing cathedral ceiling goes nonstructural wood beams and rafters > pine t&g edge and center bead nailed to 2×6 rafters > r 21? fiberglass faced > very loosely laid 1/2 eps board. Finally from above that in the attic is the structural roof overframe. I’ll attach a few photos to better describe. Its well vented from soffit and continuous ridge vent. The major issue is that the T&G ceiling is far from well air sealed. We don’t care for the dark stained edge and center bead so before I add a new decorative ceiling surface (possibly drywall, panel product, shiplap) what should be my approach to air seal. Visually I don’t want to loose too much depth of beams but my intial thought was to use 1/2″ foil faced polyiso, well sealed and then add whatever decorative ceiling choice. Or should I skip any insulation and just seal the exisiting with a smart VB? Sealing it from above isn’t possible because of the tight over frame on the south side. Half of the ceiling is angled due south, with zero tree cover and all of the sun.
Thanks
Dan
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Any sheet good will work as an air barrier as long as you can make it continuous and tie it into the wall. 1/2" plyiso is great as it is light, not too expensive, adds some R value and the seams can be easily taped. I would go even as far as going up to 2" polyiso as it would bump your assembly R vale up from ~R24 to ~R34. This would require strapping the ceiling or using long screws for the new finish.
Not sure how you would do the air barrier around the faux beams though, best to take those out and add them back in once the new ceiling is up.
You can keep the 1/2" EPS in the attic as long as it is unfaced (looks to be form the picture). If it is foil faced, it should be removed or enough gaps added so moisture can escape.
Thanks so much for the reply. The existing eps is unfaced and also not well detailed so no issues there. I'm going to make an investigative attempt at carefully removing the decorative rafters to detail the air barrier properly. They're "solid" pine but hollowed out in a u shape slipped over a 2x6 glued and nailed. If I can't remove them to save, I think i can spray from any gaps and tape to the sides up enough to be hidden.