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Shed roof insulation

1722 Views 8 Replies 4 Participants Last post by  omgdiddy
Okay reading everything online it says that 1" airspace is required from soffit to ridge in a cathedral ceiling. So installing r-13 fiberglass in the 2x4 cavities I'll need some baffles.

How do I get airflow tho to the cavities that just "end". And don't continue from soffit to ridge? Do I just insulate it anyway and leave it? And put baffles on the cavities that I can?

(Reflectix in picture is being removed and fiberglass is being installed)
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One inch is considered a minimum for a cathedral ceiling, but the resulting 2.5 inches that remains will be far short of the required minimum amount of insulation. The 2009 energy codes show NJ at r-38 for ceiling, that would be about 11" to 12" of fiberglass insulation.

That roof looks like a hip roof where the rafter channels do not go all the way to the top. Another solution may be needed.

Well I'm not too concerned about meeting energy standards. It's a shed that'll only be heated and cooled periodically. Not 24/7.

And since the floor is carpeted and the shed has stuff inside (pretty much a work/getaway building) a company won't spray foam, not to mention it's way beyond price affordability for me.

So as of now I'm thinking of just leaving the reflectix on the ceiling since it leaves the cavity open, or try installing air chutes in the areas I can and putting r13 in.

The design of the roof sucks, and even tho the roof has a ridge vent, there are no soffit vents, and they're too small to even put any in.
No drywall.
Only the reflectix loosely re installed to hold the fiberglass and act as an additional radiant barrier (it's suggested as an additional method in the instructions, as the fiberglass installed, and reflectix on the inside living space)
I don't know that I would really get too concerned on the roof ventilation in there if it's not being heated all the time. If your really worried about it, tack some 2 X 2 strips to the bottom of the rafters and then install your insulation, leaving the airspace at the top. But without any soffit ventilation, not sure if it's going to do anything for you.
Mike Hawkins:smile:
Thanks all. Here is what I did.

Walls have r13. And reflectix over it. Simple.

Ceiling I added the air chutes in the cavities that I could and continued all the way up.

The remainder of the roof I split the batts of fiberglass in half and installed it in the cavities, naturally leaving a loose air space behind it (fiberglass vs outer wall) as gravity did it's thing by pulling it outward a bit, then replaced the reflectix over it.

The reflectix itself isn't air tight by design because of all the bends/design of the ceiling. But the fiberglass is snug along the 2x4 sides.

Huge difference inside now in comfort. Went down to 47 and windy last night and it was still 68-70 without heat.
The corners are no longer drafty as the insulation stopped the air flow.
But a nice air flow/seperation is created between soffit and the top of each cavity. Ridge vent is uninsulated and hollow with just the reflectix running over the surface to allow flow behind it.

Understanding the roof should be a higher r value then about r6 (batts were split), and yet efficiency is slightly dropped, it still is a lot more insulated now and the drafts have stopped. Even a thin layer of fiberglass works wonders and will lower the heating and cooling need dramatically.
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I'm just a beginner here, but if you have a ridge vent with no intake vents, isn't your heated air just going to escape through it?
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