How to insulate angled walls with poor access?

Old 04-16-16, 06:51 PM
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How to insulate angled walls with poor access?

I've got a story and a half with knee walls and a tiny attic. The knee walls and attic are both just big enough to crawl through. I'm putting fiberglass batts on the vertical walls, blowing in cellulose on the horizontal surfaces, but I'm stuck on the angled walls. They're about 45, framed with 6" studs, 4' long, with 4 roofs worth of nails coming down. I can barely reach a hand into each one from either the knee walls or the attic. I'd really like to both insulate and leave some air flow over the top.

How do I best insulate this? I've thought of stuffing 4" fiberglass bats or rigid down there from the attic but I'm worried about them hanging on all the nails. I've also thought putting rafter vents in and blowing insulation underneath. Worst case, I could take off the drywall and do any of these options.

The first two options sound near impossible to me and the last sounds like a much bigger project.

Any opinions on the best option?
Old 04-16-16, 07:48 PM
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Actually, 1 hour and all of the drywall on those slopes will be out the window and then you can proceed to do the job right. It sounds like there is no insulation in there currently??

With 5.5" of rafters and needing a minimum air gap for ventilation you are left with 4.5" for insulation. If you use 1" rigid foam board for your air baffle (one inch foam spacers on each side) you have 3.5" left to fill with insulation. If you use either high density fiberglass (R-15) or Roxul, also R-15, then you a total of R-20. Way short of the minimum for CO, either R-38 or R-49. But those are ceiling requirements and they allow something less on the slopes. Not that less works any better on a slope, just that they realize the depth issues.

So, to your advantage, having a full width layer of rigid keeps all air flow off of the fiber insulation which doesn't improve the numbers they use, but does improve the performance which is what you care about. If you currently have zero insulation, that R-20 will be a huge improvement.

If you want or are required to go to code minimums, we can look up the slope required values and discuss how to get there. Most people making ceiling improvement on capes don't like the idea of adding 3.5" of wood to those rafters to accommodate R-38 insulation, but something like that is what code calls for.

As for stuffing fiberglass down those cavities, removing the drywall looks easy.


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