Replies

1. GBA Editor
   Martin Holladay | Jun 07, 2013 05:43am | #1

   Tim,
   If you want to upgrade your wall insulation, there are several ways you could proceed. Your decision depends on what type of access you have. If the walls are being opened up and the stud bays are visible, you can install new insulation between the studs. If the walls don't have to be opened up, you can install a layer of rigid foam on the exterior of the wall sheathing. (Of course, if you go this route, you'll need to install new siding.)

   Leaving the existing insulation materials in place will not cause moisture problems. All of the layers you describe are vapor-permeable enough that that won't trap moisture in a dangerous way.

2. Expert Member
   Dana Dorsett | Jun 07, 2013 12:10pm | #2

   Eastern WA covers quite a range of climate, much of which is altitude dependent. In case it makes a difference, what's your location (or at least your ZIP code)? Is there some type siding on the exterior ship-lap, or is it ship-lap siding nailed directly to the studs?

   There were lots of variations on the theme from 1890-1930. My 1920s house had about a half-inch of horse-hair laminated between heavy kraft, but woven between the studs (it bisected the cavity on the diagonal), which made retrofitting cellulose with out gutting a real PITA, since it couldn't be a simple drill & fill, and dense-packing alone would only fill half the cavity. I ended up fabbing up some hooks out of 5/16" steel rod to insert into a dense-packing hole to shred and remove the horse-hair a bay at a time, and yes it WAS time consuming, but less time consuming than a full-gut of the finished interior.

   I suspect you could do something similar- devise a way to shred the heavy paper air-barrier, sufficiently to be able to slip a dense-packing tube in there, and let it compress the thin batts in place. An insulation contractor probably wouldn't give you a fixed quote on it but if you drilled a 2-1/4" hole in each bay (from either the interior or the exterior) and pulled the paper yourself, the insulation bids should be slightly cheaper, since the dense-packing hole are already drilled.

   In any event, blown cellulose is preferable to blown fiberglass on this kind of retrofit, since it's more air-retardent, which makes a difference when the density at every part of the cavity is difficult to verify, and the moisture buffering capacity of cellulose is protective of the ship-lap and studs.

   But if the exterior ship-lap is also the siding, a full cavity fill might not be advisable- it may depends on your actual climate and the amount of roof overhangs, etc. It's pretty dry compared to the western slope of the Cascades, but it's not exactly a desert (at least in most places.)

3. 
   davidmeiland | Jun 08, 2013 09:32am | #3

   I'm a little unclear on the wall construction. It sounds like a fairly typical 2x4 wall until you describe that batt and the air space on the OUTSIDE of the shiplap. Is there not more framing out there to create the space for the batt and the additional air space, and to support the siding and trim? It would be good to have a photo or diagram of exactly how this was built (and was it all built at once, or was the outer stuff added on later by someone wanting to insulate?).
   I would try to go with rigid foam on the exterior if you are replacing siding and windows. You can get a much better job that way as opposed to simply insulating the cavities, and you can get a lot of air-sealing value out of it too.

4. 
   heinblod | Jun 08, 2013 11:54am | #4

   If it looks like this

   http://www.chemheritage.org/discover/media/magazine/articles/30-2-changes-in-the-air.aspx

   then leave the building. And seek professional advise.