Radiant barrier OSB and corrugated panel
Sara85602
| Posted in Energy, Heating & Insulation on
Hello All,
I have just finished sheathing on my remodel/construction project using radiant barrier OSB. The finish siding will be 26 gauge corrugated steel panels.
Problem: The radiant OSB requires 3/4″ air space between it and siding but also needs a vapor barrier. My theoretical idea is applying the barrier with furring strips (which will also be used to attach the corrugated) and perhaps attaching the barrier to top and bottom furring strips to form a “bubble” over the sheathing and under the corrugated.
Do any of the knowledgeable builders here have suggestions for the type of barrier and the best way to attach it?
Thanks very much.
Sara (in S.E. Arizona)
Country neighbor quote of the week: “Duct tape would’ve sealed those gaps”
Replies
First of all welcome to Breaktime.
I do not have an answer to your question, but this reply will serve as a bump to keep your post closer to the top of the list.
Someone will be along shortly to offer thier advice. Meanwhile, could you fill in your profile? It helpfull to know what area of the country and/climate to live in to correctly answer questions like you posted.
Dave
I'll give you another bump, and then take WAG at your situation.
I have never use radiant barrier OSB, but have used foil face rigid foam sheathing. The foil is a vp if taped with foil tape. Not sure if that is the case with foil faced OSB.
If you are in a predomenately cooling climate it is ok to have that vapor retarding membrane on the outside of the house. The purpose of the vp in that case is to retard the movement of the hot, humid outside air from entering the wall cavity as it moves toward the cooler (air conditioned ), drier enterior of the building. No vp is required on the inside of the wall because you want the assembly to dry itself out in that direction.
IMO placing a vp over your furring strips outside would be totally useless. That 3/4 air space between the radiant barrier OSB and the vp over furring is going to act like a big moisture trap. Durring the day the humid outside air will find it way into that space through all those screw and/or nail pentrations you made putting on the steel siding. Since it can't get into the sealed up foil face OSB, it just hangs around in there untill the temperature drops to below the RH dew point at night. That is when it condenses on the coolest surface available, and that will be the foil and the furring strips. Repeated cycling of that process will eventually lead to rot and mold deveolping in that boundry area.
If you are in a heating or mixed climate you don't want a vp on the outside of the wall anyway. You want it on the warm side of the wall assembly, where it will retard the movement of warm humid interior air from entering the wall as it migrates toward the cooler exterior surface.
I would use a house wrap over the OSB and follow it with the furring strips and steel siding. The house wrap will act as a moisture barrier, keeping liquid water out of the wall. The 3/4" air space and steel siding will be a drainage plane and a self vented exterior wall assembly.
I say this with some confidence because that is the way my shop is built, and I have had no moisture issues in the six years since it has been completed.
Dave
Thanks for your reply Dave.
In this particular area of AZ, the humidity generally hangs around 20% (or less) except during the rainy season. We are of course, a mostly air-conditioned place (up to 110 in July) but in a spot where it starts getting to freezing at night around mid-October.
The seams of the the radiant OSB are spaced with the recommended clips and foil taped. I would have just put up the vapor barrier as I would with traditional OSB, but two things kept me from going ahead:
1. the manuf. instructions that the 3/4" space is necessary
2.when I talked to them, they told me using corrugated was "a different application than siding", which they give instructions for on their website.
I'm going to go ahead and attach the wrap to the OSB and use the furring strips for the corrugated siding over it.
Sara
Which way is the foil facing, inside or outside? Usually you would face it inside (as on a roof), then not have the insulation touch it.
If you put vapor barier directly on the foil, you negate what the foil does and just spent too much money on regular OSB with a pretty cover that now doesn't do anything.
If the foil is on the outside:Unless I'm way off base here (other will say so) I think you should furr out 3/4" or 1" and then put the vapor barrier over the furring. Attach the corrugated panel to the covered furring. This will give you the VB as well as the radient barrier spacing.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.
Per manufacturer's instructions, the foil faces outward on walls and inward on the roof.
This is the conundrum; the 3/4" space is necessary for the radiant to work but would it negate the point of the vapor barrier if I nail it to the furring and then put additional holes through it when the corrugated goes up (as Dave suggested in his msg.)?
What do you think about tacking the vapor barrier to furring at the top and bottom?
Properly fastening VB will not negate it's effectiveness... yer not launching your house into space. The corrugagted will help pin it to the furring anyway. VB is attached with plastic cap nails or staples.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.
Paul,
As I mentioned in my intial bump post, I'm not familiar with radiant barrier osb. I'm assuming it is a foil faced product. Is that correct?
If so, and the seams are taped, why would they require and addition vp? And, by vp I mean a 6 mil poly or visqueen type product. Isn't the foil an effective vp?
Dave
No. The foil face is perforated (every 1/2") so that vapor passes through instead of accumulating inside the wood and being trapped behind the foil.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.