Wall assembly rebuild
miroland
| Posted in Green Building Techniques on
We have gutted a 19th century Italianate in Hudson, NY. The 2×4 wall bays are open to the backside of heavy clapboard siding with no sheathing. For insulation, I’m wary of using fluffy bats (either rock wool or fiberglass) because there is no WRB and the cavity will surely receive moisture from the outside. Should we use spray foam, and if so, closed or open cell? Or rigid foam with sealed edges? Or some kind WRB adhered to the back side of the siding?
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use the search bar for unsheathed walls in old houses; here's one of many:
https://www.greenbuildingadvisor.com/article/insulating-walls-in-an-old-house-with-no-sheathing
Thank you, Bob. Unfortunately the full article seems to require Prime membership, which I'm not inclined to do right now. But I gather from what is there and the comments, felt paper tacked to interior nailers will create an air space, over which insulation (fluffy, spray, or rigid) can be installed. Can you tell me if the article calls for nailers when using felt paper, or is that just for interior rigid? Thanks.
Micheal,
You cans see the article, and any other relevant ones, by clicking the Free Trial link.
Following up on Martin's article on old wall insulation, I understand that 15# felt or a house wrap like Tyvek would act as a WRB and create an air space, would they also provide air sealing if taped? I'm thinking of using batt or blown in cellulose rather than expensive spray foam. Would that work? Also, is anyone familiar with "Spider Plus" blown in fiberglass from Johns Manville?
Thanks.
Felt is impossible to seal as an air control layer. Tyvek is doable but only if you have siding off.
Dense packing (cellulose or fiberglass) does a good job of air sealing, not perfect but good enough. Just make sure whatever you are using as the vent spacer behind your siding can stand up to the dense packing pressure without bulging to the point of closing the gap.