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raymaccallum 05-02-2010 02:00 PM

removal of exterior sheathing to apply spray-foam insulation from the outside
 
Does anyone have any experience with this? I can't find any info. on the web where someone has done things this way. It's time to replace the now ill-fitting, dented and dirty aluminum siding and I'd like to address our inadequate cellulose insulation at the same time. Because there is already cellulose between the stud walls on our second floor, ideally I don't just want to pour in spray foam on top and get a poor air seal, but rather remove the sheathing, clean out the cellulose and spray-fill the cavity from the outside where I can see it all.

I don't know if our sheathing is structural or not (I'm guessing it is board and not plywood, given the age of the house). If it is structural, is it safe to remove it in sections and replace it as I work? If it's not structural, is this nonetheless a lot of work for too little gain and I'm better off pouring foam on top of the cellulose then using rigid foam over the sheathing before siding?

Thanks,
Ray

the carpenter 05-02-2010 10:00 PM

To me, topping up the walls then putting on rigid foam before siding sounds like the best option.
Any exterior sheathing , whether board or plywood, is structural. I'm sure you could rip off the exterior sheathing and apply spray foam but it sounds like ALOT more work and ALOT more mess than it's worth.

raymaccallum 05-03-2010 12:55 PM

Quote:

Originally Posted by the carpenter (Post 436827)
To me, topping up the walls then putting on rigid foam before siding sounds like the best option.
Any exterior sheathing , whether board or plywood, is structural. I'm sure you could rip off the exterior sheathing and apply spray foam but it sounds like ALOT more work and ALOT more mess than it's worth.

Thanks for your reply. Our second floor is really drafty at the floor level, so my concern with the 'top-up' option is that it leaves the cellulose at the floor level (albeit more compacted by the poured in foam). Do you think that the air barrier and thermal break provided by rigid foam on the exterior will markedly reduce this problem?

the carpenter 05-03-2010 09:47 PM

yes I do. We've been doing alot of rigid foam on the exterior even in new construction. It makes for a very tight house. I've said before in other posts, I'm not completely sold on using a rigid product that isn't breathable in place of Tyvek. If moisure gets in, how's it going to get out? Then again, how's it going to get in either. Anyways, food for thought.

JIreland 03-24-2011 05:52 PM

We did it at our place
 
We removed the asbestos shingles, tar paper and 1x sheathing and sprayed BASF 2lb in our 1920 bungalow in Calgary, Alberta. We also did the same procedure at our friends 3 storey 1909. It is a ton of work, but I thought it was the right thing to do and we contributed all the labour ourselves so the cost was actually less than paying the extra for a icynene pour formula (which only one contractor we talked to would do. This contractor charged extra for the pour formula, gave no guarantees and would not be responsible for leaks into the house.)

Our house also had bracing at each corner which was basically a row of blocking in 10 stud bays cut at a 45 degree angle working from the double top plate to the sill plate. This would have rendered the pour formula useless for about 20% of the wall area.

Our house is now much warmer, and our gas bills (we had no insulations at all before) are down 75% in the winter (R50 in the attic, new windows and a new furnace also helped I bet). We have cold spots around the floor at the exterior but that is because the 1x subfloor runs through under the sill plate and there is very little we could do to insulate this weak spot.

In our next house I will use rigid foam on the exterior as well and lap it right over the rim joists hopefully to stop this problem as well as the inherent thermal bridging that always occurs at rim joists and beams.

Send me a PM and I can send you some picture of our house while the process was taking place.


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