How to insulate garage walls from the outside?

Question

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)?

Answer 1

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.