Radiant Barrier on Cabin Roof - layer confusion


Old 04-01-08, 11:53 AM
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Join Date: Apr 2008
Location: USA
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Cool Radiant Barrier on Cabin Roof - layer confusion

Hello there,

So I have an old cabin the the Santa Cruz mountains. It gets hot in the summer and cold cold in the winter. I'm looking mainly to warm it up. Will do other insulation work but the roof is my main puzzle.

The roof is exposed trusses, redwood plank deck, felt paper and asphalt shingles. I'd like to maintain the exposed wood inside to keep with the cabin feel so I'm trying to figure out how I can at least gain some benefit with minimal insulating above the decking.

I've mentally come up with the following scenario. If anyone can add or provide changes/pointers, I'm all ears.

Trusses, redwood planks remain. Above that I keep the felt (because its black and doesn't show in the cracks of the deck beneath it when looking up at the ceiling from the inside.) Radiant Barrier, Wood strapping 2x2's or 2x4's for taller space, OSB/Ply deck, Felt again and then asphalt shingles.

Would this have any benefit or should I use Radiant barrier with a foam board to help insulate? In the above scenario would the condensation stay on top of the felt which covers the redwood decking.

redwood plank decking
R barrier
wood strapping
Asphalt Shingles

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Old 04-01-08, 01:04 PM
airman.1994's Avatar
Join Date: Dec 2005
Location: VA
Posts: 5,632
RB will not help you keep the heat in! You need something with R- value.
Old 04-02-08, 09:31 PM
Ed Imeduc's Avatar
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,389

Some here have put the truss up then the redwood plank decking. On top 2X2 nailers. fill in with polystyrene sheetsthen the OSB felt and shingles.
Old 04-02-08, 10:22 PM
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Join Date: Apr 2008
Location: USA
Posts: 9
2x2 and polystyrene

I've seen a few articles about adding the R Barrier on top of decking with 2x2's. I thought I'd throw in the insulation as an added bonus. I guess I'm wondering if both R Barrier and the polystyrene would help for both summer and winter...
thanks for the reply.
Old 04-14-08, 06:21 PM
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If you are mostly concerned about cold weather think of your home as an insulated box. You will most definitely need bulk insulation and a tight envelope to minimize heat loss and air infiltration. Radiant Barrier can be used effectively to make the bulk insulation more effective. You would want to get it as close the to the interior living space as possible while providing an air gap on at least one side. There are different methods to achieve the air gap as mentioned in an earlier post.

Here is an illustration. If you put a hot casserole inside an ice chest it would stay warm for a certain amount of time. If the ice chest was LINED with FOIL (radiant barrier) then it would reflect more heat back to the interior and stay warm even longer. Therefore, making the ice chest (bulk insulation) more effective. This is how foil insulation can help in colder climates. I've had many customers put atticfoil behind sheetrock, then create an air gap between the foil and the bulk insulation (spray foam is best) with great results. This is especially true if you are using some kind of radiant heat source rather than a forced air method.

Stay Cool!

Last edited by the_tow_guy; 07-16-08 at 09:37 AM.
Old 04-14-08, 10:29 PM
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Join Date: Apr 2008
Location: USA
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Thumbs up spacers

So then in order to create the gap I could lay the RB down on redwood deck, Put the 2x4's down and then 1x1 beading flush to the RB and against the inside of each 2x4 to hold the polystyrene an inch above the RB and close to the layer of OSB decking above. Would that space also work well for the airflow...
Thanks for the input..
Old 04-15-08, 06:10 PM
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I'm not quite clear how you intend to do this. You are going to need some type of bulk insulation. You mentioned foam board. However, you would need to seal the air space to create "dead air" if you want to incorporate a radiant barrier. Are you planning on venting beneath the foam board? If so, the foam board will basically do nothing as far as insulation. (this is where I'm unclear about the airflow comment)

I'm all in favor of using radiant barrier when possible. But for your application you might just want to go with ISO board over the existing roof deck, seal all the seams (actually go two layers and offset the seams horizontal and vertical) to prevent air infiltration and then put a new deck on with new felt and shingles.

Here is some good info from BuildingScience.com about this type of non-vented roof assembly.

Stay Cool!
Old 04-16-08, 11:39 AM
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Join Date: Apr 2008
Location: USA
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Thanks for the input. You're absolutely right. That makes perfect sense. Thanks for the input. I guess I'll save the RB for sealing in the subfloor and save a few bucks.

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