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Insulating Pipes Inside Insulated Walls with Two Air Barriers

jamesboris | Posted in General Questions on

Zone 2A. I’m running PEX-A hot & cold water pipes through walls (densely) insulated with fiberglass. Should I also put pipe insulation on the pipes?

This may sound silly, but I’m thinking that although the fiberglass will prevent heat loss, I’ve detailed both my exterior sheathing and my interior drywall as air barriers… and I want to be sure there’s no chance of condensation inside the wall.

Problem is, if I put insulation around the pipes, which are PEX-A, then I’d have to drill extra large holes through my studs to fit them… but I can’t do that (load-bearing wall), so the insulation would have to start and stop. I’m probably overthinking this — I’ve insulated plenty of pipes in my time, but this is the first structure I’ve dealt with that has 2 air barriers. Thanks!

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  1. Expert Member


    I don't see much point in further insulating the hot water pipes - especially in Zone 2A. The risk of condensation is on your cold water pipes if warm, moist air can reach them. If you decide to insulate any of them, just stop at the studs to avoid problems with the hole size.

  2. Expert Member
    BILL WICHERS | | #2

    If you've sealed the wall up well, you shouldn't have enough moisture getting in there to cause any problems. If you're worried, use the regular split pipe insulation, ideally the kind with and adhesive strip one edge so that you can seal it around the pipe. You don't need the insulation to pass through framing members -- just end the insulation tight against the side of the framing and start again on the other side with a new piece of insulation. The small amount of pipe going through the wood won't really be an issue, and the wood itself is enough of an insulator to keep condensation at bay.


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