Insulating walls in an old house
I have an old house which I bought last year in Asheville, NC(Zone 4). I insulated the attic with blown-in cellulose to R-40 and now I am ready to figure out the walls and crawlspace/floor.
The exterior walls of the house have no insulation. There is vinyl siding on the house right now.
I have heard that blowing in cellulose into the walls can lead to mold and rot.
I am considering having fiber-cement siding(hardiplank) put on the the exterior of the house in the next few years.
What do people recommend for insulating the walls?
Should I just wait and add foam boards to the exterior of the house before putting on the new siding?
Should I put up foam boards on the interior walls(this is possible-the original planks are exposed right now).
If I blow in cellulose and add exterior foam boards and fiber-cement siding later will I have a mold/rot problem?
Thank you.
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Replies
Wyatt
Wyatt,
R-49 (or more) in the attic would be better. What is under the vinyl siding? Please describe the wall from outside to inside.
I do not know exactly what is under the vinyl siding but I believe there is a layer of shingles. I thought the attic insulation R-Value recommendation in North Carolina was R-38. Right?
I will find out exactly what is underneath the siding and post soon. Thank you very much.
Local codes vary but GBA usually recommends R-49 for Zone 4. Is there an area on the interior where you can peek into the wall and see how it’s put together?
Minjen,
Whoever told you that insulating stud bays with cellulose can lead to mold or rot is mistaken. Here in New England, dense-packing the walls of older homes with cellulose is routine. For more information on this work, see How to Install Cellulose Insulation.
Dense-packing your stud bays with cellulose has two benefits: it increases the R-value of your walls, and it cuts way down on air leakage.
If and when you decide to install new siding, you can add exterior rigid foam to your walls if you want to. For more information on this work, see these articles:
How to Install Rigid Foam Sheathing
Roofing and Siding Jobs Are Energy-Retrofit Opportunities
With the vinyl siding you meet the IRC definition of "vented cladding", which gives offers a more than adequate drying path for the wall assemblies in zone 4. Even if you moved the house to zone 5 it would still not need an interior vapor retarder tighter than standard interior latex paint(!).
https://up.codes/viewer/utah/irc-2015/chapter/7/wall-covering#R702.7.1
If the window flashing is absent and bulk moisture can get in there is some risk of mold below the windows but it will be very localized, not a generic problem with the stackup. Deep roof overhangs or window awnings can mitigate that quite a bit, but when it's time to re-side it's still worth rectifying any missing flashing.