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Got an idea I want to run by you folks:
Want to add insulation in the attic (old house).
Want to be able to use the attic for storage and have some kind of walkable surface (so blown-in or batts would be difficult to live with).
Already have R15 Fiberglass in the attic floor joist bays (2×4 construction).
Sistering taller joists won’t be a good idea because: they don’t rest on the top of the walls (there’s a 3ft section of roof between them) and I worry that the added load would cause trouble (roof is 2×4 construction too).
So my idea is: lay 3″ foam panels (Owens Corning Extruded Polystyrene – the pink panels or Foamular, both are made with Isocyanurates, which I hate, for the environment, but I digress) over the joist bays, then 1/2″ OSB on top of that for some resistance to footprints and voila, I end up with an R30 ceiling. And usable storage space too.
Now, is there something I’m missing or is it really that easy? I know that foam panels are more expensive than FG Batts or Cellulouse so its not usually used this way but other than that it should be ok, right?
Actually, living in Michigan, I would like to get R40. Any good ideas other than 2 more inches of foam? Oh, the head room up there is not great as it is, so if I use up too many for insulation I’ll lose real storage potential (extra clothes, old boxes, lightweight bulky things).
I already sealed the basement ceiling (plugged any holes with rock wool, confirmed a dry basement (40 ~ 60% RH year round), and sealed the attic floor with fire-rated caulk. Also filled all plumbing / wiring chases with packed cellulouse. The house is heated with steam, so no duct-work issues to worry about. So I am hoping that moisture won’t be a problem, but plan to check up there from time to time.
Anyway, you know how it is, you want to do a project but just want to run it by the experts in case you overlooked something vital.
Thank you for your time, and any advice you might have. What a great web-site this is.
Replies
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Got an idea I want to run by you folks:
Want to add insulation in the attic (old house).
Want to be able to use the attic for storage and have some kind of walkable surface (so blown-in or batts would be difficult to live with).
Already have R15 Fiberglass in the attic floor joist bays (2x4 construction).
Sistering taller joists won't be a good idea because: they don't rest on the top of the walls (there's a 3ft section of roof between them) and I worry that the added load would cause trouble (roof is 2x4 construction too).
So my idea is: lay 3" foam panels (Owens Corning Extruded Polystyrene - the pink panels or Foamular, both are made with Isocyanurates, which I hate, for the environment, but I digress) over the joist bays, then 1/2" OSB on top of that for some resistance to footprints and voila, I end up with an R30 ceiling. And usable storage space too.
Now, is there something I'm missing or is it really that easy? I know that foam panels are more expensive than FG Batts or Cellulouse so its not usually used this way but other than that it should be ok, right?
Actually, living in Michigan, I would like to get R40. Any good ideas other than 2 more inches of foam? Oh, the head room up there is not great as it is, so if I use up too many for insulation I'll lose real storage potential (extra clothes, old boxes, lightweight bulky things).
I already sealed the basement ceiling (plugged any holes with rock wool, confirmed a dry basement (40 ~ 60% RH year round), and sealed the attic floor with fire-rated caulk. Also filled all plumbing / wiring chases with packed cellulouse. The house is heated with steam, so no duct-work issues to worry about. So I am hoping that moisture won't be a problem, but plan to check up there from time to time.
Anyway, you know how it is, you want to do a project but just want to run it by the experts in case you overlooked something vital.
Thank you for your time, and any advice you might have. What a great web-site this is.