Roof now has 1/2″ plywood on eaves and rakes with 1/2″ OSB on main field of roof, in northwest Wa.
I wish to reroof with 5/8″ plywood do to moisture issues.
Wouldn’t it be more structurally sound to start at eave and rake bottom corner and run the 5/8″ ply continueously, perpendicular to 24″oc roof trusses, eliminating having to fill in pieces do to 20″ rakes.
Staggered ends of 5/8″ ply would fall at 24″ though and not 48″ in this case do to 20″ rakes where excess would be trimmed off.
Would this be acceptable and/or beneficial?
Replies
I can't think of a reason why only the eaves and rakes would be
plywood. I don't think I've ever seen a roof decked with two different materials except when the deck was exposed at the overhang and a better looking material than OSB or exterior plywood was used.
I'd start with the plywood on the lower corner, let the 4" run past the fly rafter and trim it later. And proceed from there.
resheathing roof
Thanks for your response JimB,
I think the builder was cutting corners/cost.
The ply on the rakes and eaves are exposed under 20" overhangs. There is a 2 birdhole block vent per each 24"oc rafter bay.
Your method is exactly what I was implying...made sense to me.
Align your first sheet with the rake edge, then push it farther out as far as needed to center the other edge over a rafter. Trim off the excess. For the next course (of course) stagger the start by 24 or 48 inches.
You want the ply on the ends to extend at least from rake edge over the gable rafter to the first inboard rafter. As you approach the other end, if you notice that that won't happen, put a shorter piece somewhere in the "field" to compensate.
resheathing roof
Thanks for your reply also, DanH.
Your suggestion concurs with JimB's and my thought proccess.
I have read that with 5/8"ply it is not neccesary to stagger ends but I feel if not by 48" than 24" is better than no stagger at all.
Also, I didn't feel comfortable with the seam over the gable rafter or eave.
I drew it out on paper and with my dimentions (63' length by 20' to ridge) it should take 40 sheets of ply for back half, with 10 end cuts (4" and 28" opposite end) and 8 rips across top, at ridge for continuous vent. No short filler pieces neccesary, if my calculations are right.
Now, because of a NRA article I read, that I should have bookmarked, (Google search) stating that felt paper will be fasing out by 2014; what are your thoughts on ice & water shield and/or synthetic like "Feltex" for underlayment with laminated shingles vs. 15 lb felt. (Region 4C Northwest WA)... rains alot here in this upper northwest corner.
"Moisture issues"?
The roof sheathing system you describe has been the standard here in Western WA for at least since the late 70's when I came out here. We used to use 1/2"cdx in the field, then switched to o.s.b. sometime in the mid 80's or so. The cc grade plywood is used around the perimeter because we use open soffits and exposed rafter (truss) tails and it looks more finished.
What "moisture issues" are you having that you need to resheath the entire roof?
Look at RoofTopGuardII or Titanium UDF50 for synthetic underlayment. Both have been used by many people here with great results (I like the Titanium myself - haven used the other yet)
The synthetic underlayments are WAY berrter than felt. I have used Titamium UDL and Feltex with great results. they are more expensive than felt, but much stronger. Why does it matter? I recently had a patch of shingles blow off in a near 100 mph wind event. It was the middle of winter, and the wind was followed by a solid month of snow and sub-zero temps, so I souldn't get up there and fix the roof. Even with the missing shingles, I had zero leaks in the roof. Neighbors who had felt had major water damage from leaks because the felt blew off at the same time the shingles did. You could see the plywood/OSB on their roofs and mine all you could see was the gray Titanium UDL.