Sheathing thickness variations and cedar shingles

[Wayne Whitney]

Hello,

Short version: if my sidewall sheathing varies in thickness by 5/32", is that a problem for applying cedar shingles, or can I shingle right over that difference? I'll be using shingles with an exposure of

4.25" and a butt thickness of 0.45".

Long version: my house currently has 7/8" plank sheathing and cedar shingle siding. The shingles needs replacing, and since I'm in earthquake country, I'm going to resheath most of the house with 1/2" Struct 1 CDX plywood. I also plan to use a 1/4" thick rainscreen mesh (Home Slicker) on top of the new sheathing.

Now there are places where I'd prefer to leave the old sheathing, like around windows and doors so I can leave the trim in place. The new buildup will be 15/32" + 1/4" = 23/32" thick, or 5/32" less than the old sheathing.

If that difference is too great, I could either use 5/8" CDX (20-40% more expensive), or use horizontal furring strips (a hassle). Any other ideas? It's too thin for 1/4" foam board.

Thanks, Wayne

[tom]

Take a few of those cedar shingles and cut them down to use as transitions betwixt the high and low spots. You really only need them where the shingles will be nailed to the sheathing( ie: every 4.25 inches). Then shingle right over them. Tom

[Goedjn]

Thin layer of low-expansion spray-foam, scraped to flush.