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I have a partially finished double garage that has no insulation in the exterior walls. Half the garage (10'x20') is finished and is now my office, and half (also 10'x20') is now a workshop. The dividing wall that I put up in the garage does have insulation, so we're just talking about exterior walls. There is a bonus room above the garage, so I have no access from above, if that matters.

My plan is to remove the T-111 panels from the outside of the house, cut the tyvek house wrap, lay the batting in the walls from the outside, then put back the wrap and T-111.

For the record, I have removed and reattached a couple of the T-111 panels before without incident, but didn't have the time/foresight to deal with the insulation issue back then when I did it.

Are there any downsides to doing the insulation from the outside as opposed to taking down the drywall inside, or cutting holes in the drywall and blowing insulation in? Any special procedures for putting back (or replacing) the house wrap? Can I just seal the cuts in the house wrap with some kind of tape, or do I need to fully replace it (though it seems like I would still need some sort of tape there)?

  • Insulating from the outside will make it easier to seal electrical boxes that are installed on the sheetrock side, so there's that. I haven't done this, so not sure of what problems you might face. – JPhi1618 Jul 18 at 16:21
  • What are you doing for inside vapor barrier? – isherwood Jul 18 at 16:34
  • If an older home the “house wrap” may be tarpaper or felt if it is I would replace it with a tyvek or modern barrier. – Ed Beal Jul 18 at 16:38
  • Why would you insulate the interior dividing wall? – Sickest Jul 18 at 17:00
  • @Sickest Because it's between my air-conditioned office and the un-air-conditioned workshop/garage area. – Haydentech Jul 18 at 18:49
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I see no problem with your plan. I asked about vapor barrier in a comment, and since you're not using any that concern is moot. It makes no difference which side you install fiberglass batts from.

I would make a minimal number of strategically-located cuts in the housewrap. If you can cut over lumber you'll be able to tape them (using approved housewrap tape) fairly easily. If you can't, I'd consider installing strips of housewrap across the cuts and taping those edges over framing, where you can press it tight for a good seal. Lap all joints with water flow in mind, of course.

  • I agree , for your sake I hope they did not use ring shank nails on the T1-11 they can be a bugger. As Isherwood states to seal any cuts in the tyvek and also use this opportunity to seal around window flashing if that was not done originally.+ – Ed Beal Jul 19 at 15:06

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