cedar shingles applied over rigid insul?
charlie44732377
| Posted in Construction Techniques on
Hi Guys
Constructing a woodworking shop with office space on 2nd floor:
I would like to sheath with 1/2″ CDX or OSB over 2×6 frame, then apply either XPS or ISO (1″) over sheathing, then apply cedar shingles over the rigid insulation. (see “Save energy with Rigid-Foam Insulation”, FHB Aug. ’06)
Two concerns: 1-Will shingles be secured strongly enough when nailed thru the 1″ insulation (I know it’s not ideal, but will it be strong enough). 2-Moisture concerns affecting the backs of the shingles: I would not put a vapor barrier on the inside of the walls. XPS is considered a moisture “retarder” and ISO a moisture barrier.
I really don’t want to apply nailing strips for the shingles on the outside of the rigid insulation.
Thanks Charlie
Replies
Why don't you want to install nailing strips?
extra time and money and it won't address my 1st concern regarding how strongly attached the shingles will be through the 1" foam
charlie
You probably should keep the vapour retarding materials on the inside anyway.
Unless you have enough insulation inboard of the foam so that there is no possibility of a dew point ever occurring inside the wall cavity, you are simply asking for trouble by putting that foam on the outside.
Ron
The nailing strips help the shingles dry by having an air space behind them.
what climate?
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Massachusetts North Shore on coast
In that climate, the shingles won't last ten years applied ddirect tight to foam like that. Water will be blown into the material and will be retained at the backside. The surface will dry faster and the shingles will cup out like crazy while the backs stay damp and rot.as for the Q of how well they would stay attached, that depends on the length of nail you use.
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Charlie,
I did what you suggest at my own Vermont house 27 years ago. But I installed 1x3 horizontal nailers every 5 inches up the wall, corresponding to the 5 inch exposure of my cedar shingle siding. I screwed the 1x3s through the foam to the diagonal board sheathing under the foam. I wouldn't attempt to install the shingles directly on foam, without the 1x3 nailers, though. The shingles will last much longer if they can dry on both sides. My siding is in great shape -- never been painted or stained -- and the wall is perfectly dry (I had to open up a wall when I added a window a few years back).
You got it right.
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If you dont want to apply nailing strips there is this allternative:
http://www.benjaminobdyke.com/html/products/slicker.html
Dont know the cost dif vs 1x3 but you should do one or the other. What Piffin said is absolutely going to happen, especially with you being on the water. Another thing that will go a long way towards longevity is getting them pre finished. Check out the warranty
http://www.cabotstain.com/cabot/products/siding_factory.jsp
http://www.maibec.com/eng/pages/siding/Maibec_Brochure_eng.pdf
Thank you "reinvent"Good advice. Cedar shingles bureau recommends applying directly over 30# felt; not sure why it would be different over rigid insulation in regards to the moisture problem.I have installed red cedar shingles on my house and I stain them myself with a neat little handmade dipper with 2 paint rollers above the small vat of stain--like an old ringer washer, the drying them by sticking the narrow ends in an upward tilted series of grooves in boards on a fence--works great, I should patent it.I'm in the process of checking out "homeslicker" on that website you suggested, but am a little worried about all the "fluff" between the shingle and the sheathing.Thanks again Charlie
"directly over 30# felt; not sure why it would be different over rigid insulation in regards to the moisture problem"Two comments there - Do a little research in the materials data and safety sheets and you will find that the EPS foam panel is a lot different from 30# felt.I have also found cedar shingles to harbour rot on their back sides when applied against tarpaper and then stained or painted. Water still penetrates, but cannot wick back out as easily so it is traped there. These were siding jobs about 25-35 years old
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"Cedar shingles bureau recommends applying directly over 30# felt; not sure why it would be different over rigid insulation in regards to the moisture problem."
First, I don't understand why you'd consider placing the foam board on the outside rather than the inside, where a vapor retarder belongs in a heating climate. By the way, anything with a perm rating less than 1 is considered a vapor retarder, which includes all rigid foam boards with the exception of expanded polystyrene (or sprayed in place icynene).
Second, cedar shingles MUST breath, which is why the best roof installations are on skip sheathing with interlaced felt membranes. On sidewalls, felt underlayment will be the best option (short of cedarbreather or house slicker), as it is an effective rain and air barrier but is hygroscopic and will wick moisture away and allow vapor diffusion in either direction. In other words, it will allow drying whether wetting is caused by environmental leakage or by vapor migration from inside.
In fact, felt underlayment functions better than the high-tech housewraps, which can create a condensation surface for outward-migrating moisture if there is any void between sheathing and siding, and will then trap liquid water between sheathing and air barrier, with no drainage plane such as with shingled (overlapped) felt or building paper.
the reason I don't want to put the rigid insulation on the inside is that, being a shop, I want to be able to screw lots of shelves, hangers etc on the walls and attachments wouldn't be as strong when made through 1 1/2" of insulation and sheetrock. But I might have to, huh? What about 30# felt over the rigid insulation on the outside? Or like I think I mentioned, shingles over homeslicker over the rigid insulation on the outside?Thanks so much Charlie
Felt over rigid foam board won't allow the back of the shingles to breath (release moisture) because there is no hygroscopic layer under the felt to wick the moisture away.
Placing a layer of Homeslicker between the foam and the shingles will allow breathing, but I would be skeptical about the stability of small diameter shingle nails that have to penetrate 1-1/2" or more before hitting wood, and you'd still have a wrong side vapor barrier.
It's easier to screw or lag in ledgers on the inside to attach shelving, etc, and drywall screwed through an inch of foam is more stable because it is a large membrane which doesn't move with moisture changes as shingles do.