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Question about roof insultaion in unventilated shed


mjricha's Avatar
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Join Date: Mar 2017
Posts: 2
FL

03-18-17, 12:14 PM   #1 (permalink)  
Question about roof insultaion in unventilated shed

Hello,

I have searched the forum and I can't find an answer to my problem, so I was hoping I could get some advice.

We just had a 10x14 Tuff Shed Installed in Central Florida. It is very hot and humid here and we wanted to insulate it and condition the space (for a work room, she-shed, etc). So when we ordered it, we ordered it with a white metal roof, hoping to reflect a lot of the heat. We ordered the shed UN-ventilated, because I was under the impression that the metal would be exposed on the interior of the shed. The plan was to closed cell spray foam the exposed metal.

However, the installation was OSB with felt and THEN the metal roof, with a radiant barrier underneath. We didn't pay any extra for the radiant barrier, I guess it came included with the upgrade cost of the metal roof.

We wanted to make a loft in the shed as well for extra storage, but the radiant barrier poses a problem. I have read here that you cant spray foam a radiant barrier. If we install a traditional drop ceiling and insulate with fiberglass, we lose the ability to have a loft, and we will have to cut holes in the sides of the shed for ventilation. We would rather not do that.

Any advice on what to do? If it would be better to spray foam the ceiling anyway and lose out on the radiant barrier, that would be fine as long as we achieve a high enough R value. I am not trying to spend a fortune cooling this thing.

Thanks!

 
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Marq1's Avatar
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03-18-17, 01:17 PM   #2 (permalink)  
I've read this post 3 times and I'm still not sure what the issue is and what the OP is looking to do?

 
Bud9051's Avatar
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ME

03-18-17, 01:38 PM   #3 (permalink)  
I'm on my second trip through so I'll summarize and ask a question or two.
1. A 10 x 14 will not cost a fortune to cool even with minimal insulation.
2. The roof as I take it is metal over osb with a RB on the inside, but not sure if the RB is attached to the bottom of the sheathing or across the bottom of the rafters.
3. A "Tuff Shed" looks to be just a home Depot brand of a regular stud framed shed.

Your only concern in your climate would be cooling an exterior surface to the point where the high humidity would cause condensation, a low risk.

Tell us where the RB is currently installed.

Bud

 
mjricha's Avatar
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FL

03-18-17, 02:05 PM   #4 (permalink)  
Sorry, Ill be more specific.

From the top down:
White metal roof
Tar paper
OSB
Radiant barrier
Ceiling Joists.

The radiant barrier is attached to the bottom of the sheathing

My question was, If I spray foam in between the celing joists, I would be covering the radiant barrier with spray foam. I have heard this is bad and will negate the radiant barrier. Is this true?

If so, will having the spray foam insulation even be worth it if the effects of the radiant barrier are negated?

Sorry again, hope this helps

 
Bud9051's Avatar
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03-18-17, 05:26 PM   #5 (permalink)  
@mj "If so, will having the spray foam insulation even be worth it if the effects of the radiant barrier are negated?" Yes, there must be an air gap for the RB to have any value. But, that loss is easily compensated for with the spray foam.

Spray foam for a small project isn't inexpensive and requires a DIY approach because the large contractors usually don't want little jobs. Since this isn't living space I believe the thermal barrier to cover the foam does not apply but check local authorities, local codes rule.

An easier and less expensive approach might be to cut and fit rigid foam into the rafter cavities, In fact you could use a foil faced foam and get back some of the RB value lost.

Bud

 
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