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Community and Q&A

Insulating a House with Wood Siding and No Sheathing

HMNola | Posted in Energy Efficiency and Durability on

We’ve recently purchased an old 1850’s house in Louisiana (raised, shotgun style). It is structurally in really good condition. The wood siding does need some repairs, but not so many that it makes sense to strip the whole thing (in which case we could sheath it and replace with hardie board). Also, we want to preserve the quality old wood wherever possible. So it has wood siding nailed directly to the 2×4 studs with no sheathing, no insulation, and then drywall inside.

We don’t want to live in a leaky sieve that costs a fortune to heat and cool, but I also do not want to create an environment for mold and rot because I do not have proper barriers in place. The climate here is very hot and humid and I’m gathering that one of the reasons that old houses can last so long down here (besides the superior wood used in framing during that period) is because they have been allowed to “breathe.” My head is swimming with researching the different types of barriers (air, vapor, thermal) and how condensation happens, and where air flow is necessary, and where it’s bad, and I’m just very overwhelmed.

Has anyone dealt with a project like this in the south, and what were your solutions? Someone recommended pulling all the siding off, scraping and back-priming it, wrapping the house in tyvek, and then putting it back on. I’ve also read about creating an air barrier between siding and insulation with spacers and foam boards. I’ve wondered about leaving the cavity open and making the walls really thick plaster.

Also, the house is almost 2000 sq ft with 11 ft ceilings, it’s not just a little cabin or a room. We thought we’d save money by keeping the old siding but now I think we’ll just have to pay that much more to insulate it.

Any guidance greatly appreciated.

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  1. Expert Member
    CARL SEVILLE | | #1

    In your climate the return on insulating the walls isn't worth the cost, unless you are planning to remove the interior drywall and expose the stud cavities. The temperature differential between interior and exterior rarely gets high enough to make it viable. If you do an exceptional job of air sealing the envelope with caulk and foam sealants at all gaps in the drywall walls, remove attic insulation and seal top plates to drywall at interior and exterior walls and around all lights and pipes, and seal the floor or create an enclosed crawlspace your house should perform just fine. Eliminating the air leakage will help manage the humidity and heat movement in and out and keep the house fairly comfortable.

  2. HMNola | | #2

    Thanks Carl. We actually are planning to open up the drywall, because of changing interior walls, and replacing/reframing rotting windows. With all the stud cavities open, is there a good way/product to insulate directly against the back of the siding?

  3. Expert Member
    CARL SEVILLE | | #3

    Look at this post from last year: I installed felt paper stapled to the studs then installed spray foam which provided a great air seal.

  4. Expert Member
  5. HMNola | | #5

    Thank you!

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