roof sheathing

[billconner]

My search here for roof sheathing didn't yield much - probably wrong terms.

Small hip roof porch addition - probably not on piece of ply not cut - all hips and valleys - 9 pieces total. Unheated and 60 PSF dedign snow load. Asphalt shingles. 16" o.c. rafters. Metal "W" valleys.

I prefer CDX ply but open to arguments for OSB? Some articles claim OSB is stronger.

Nominal 1/2" or 5/8"? Was planning 1/2" CDX but now leaning toward 5/8" CDX. Working alone at 73 years weight is a consideration.

Thanks in advance!

 

[pcmeiners]

Replaced sheathing on a number of roofs, never used anything but 5/8" plywood . Years back all the new house construction in NYC used 1/2" ply which proceeded to have the plies delaminated due to condensation. Basically after that occurred you needed to know where the roof rafters were or else you fell through what was left of the plywood. As to weight it is not fun at upper age, but 1/2" is only a little less "fun".

 

[billconner]

Replaced sheathing on a number of roofs, never used anything but 5/8" plywood . Years back all the new house construction in NYC used 1/2" ply which proceeded to have the plies delaminated due to condensation. Basically after that occurred you needed to know where the roof rafters were or else you fell through what was left of the plywood. As to weight it is not fun at upper age, but 1/2" is only a little less
"fun".

Probably not condensation over an open porch but understood. Underside of existing porch roof looks brand new at over 30+ years.

 

[mike93lx]

I'd be doing zip sheathing. Either thickness would be sufficient, especially for a little porch and 16oc.

I wouldn't be running 5/8 ply. Too heavy and no real benefit for this, IMO

 

[Firebrick43]

Advantec osb is phenomenal even compared to cdx.

5/8 is much stiffer and doesn’t telegraph where all the panel joints are like 1/2” does when the sun comes out on a cold roof

 

[Kaizen]

also a fan of zip. I like it as if it gets wet its not a big deal. I used 5/8 on my shop but that per sheet is heavy. 1/2 zip will meet code on 2 foot stud spacing. Definitley cut on the ground and push the pieces up ahead of you on the ladder. Dont forget the seam tape

 

[MushCreek]

I used 5/8 OSB on my house, 2' centers, and it's very strong. Heavy, though. 66 lbs. a sheet if I recall.

 

[PopcornSutton]

Go 1/2" OSB with clips between joists. Much better since you're doing 16" centers.

 

[PCustoms]

I'd be doing zip sheathing. Either thickness would be sufficient, especially for a little porch and 16oc.

I wouldn't be running 5/8 ply. Too heavy and no real benefit for this, IMO

also a fan of zip. I like it as if it gets wet its not a big deal. I used 5/8 on my shop but that per sheet is heavy. 1/2 zip will meet code on 2 foot stud spacing. Definitley cut on the ground and push the pieces up ahead of you on the ladder. Dont forget the seam tape

Zip or adventek.

At 16" O.C. 1/2 is likely fine.

I'm about to donate small eyebrow and have a sheet of 1/2 zip left over from something else, will probably use that

 

[billconner]

I appreciate all the input. I'm probably going to go with 1/2" (7/16) CDX. The existing roof is 1/2" OSB, looks new on underside, and was installed on 1994.

 

[carlaisle]

1/2" CDX will be fine with 16" spacing. Sure, 5/8" is "better", but you're not really getting the benefit out of how much better it is at that spacing.

I have seen the arguments that OSB is stronger, but am unmoved. I've seen mother nature turn too much OSB into sawdust without the use of a saw.

 

[finn]

Check your local code. Inspector here insisted on 5/8”. Everyone uses OSB for roof sheathing here.

My shed, put up about 30 years ago, has 1/2”, and needs resheathing because of warping and cupping. House is 5/8” and is fine.

 

[mike93lx]

Check your local code. Inspector here insisted on 5/8”. Everyone uses OSB for roof sheathing here.

My shed, put up about 30 years ago, has 1/2”, and needs resheathing because of warping and cupping. House is 5/8” and is fine.

I've had two houses now with 7/16 osb and 24oc trusses... Roofs are flat.

 

[finn]

I've had two houses now with 7/16 osb and 24oc trusses... Roofs are flat.

Pretty mild climate, I presume.

What does your code require. 7/16 wouldn’t even come close. You’d never get an occupancy permit.

 

[mike93lx]

Pretty mild climate, I presume.

What does your code require. 7/16 wouldn’t even come close. You’d never get an occupancy permit.

Massachusetts and virginia.

Pretty mild is relative, but I don't think MA would fall into that bucket.

No idea on code, I don't build houses

 

[billconner]

I know nominal 1/2" meets code and was shown on drawings for permit.

On my garage I use rough sawn 1x10s - very nice to work on and less expensive than panels.

 

[nadogail]

Many buildings have been sheathed with Shiplap.

 

[billconner]

Related after looking at existing roof more I think I have to tear off 2 layers. A little over 3 square. It's been a while since I've done reroofing but might be up to it once more.

If I do tear off, can I put down peel and stick/ice and water over whole porch roof and expect it to be Ok for a few weeks? I'd like to do full tear off, then build addition, then install roofing all at once.

I may hire it done - just because of tear off - but investigating options.

It is 4/12 or very slightly less on addition, and last one was 8/12. I hope the lower slope compensates for 30 years.

Also, smallest dumpster I can find is 10 yd and over $750. Any other strategies for getting rid of tear off?

 

[jkeyser14]

Pretty mild climate, I presume.

What does your code require. 7/16 wouldn’t even come close. You’d never get an occupancy permit.

I'm in Maryland. Hot and humid in the summer, snow and ice in winter with up to a couple feet of snow build up. We also have 7/16 with 24" OC trusses. Pitch is 12/12 on front of house, 10/12 on rear.

House is 8 years old and no issues so far.

I did climb the roof when I did my final walkthrough and the sheets are very bouncy, but bouncy doesn't mean bad .

 

[carlaisle]

Not sure of your exact location, but this came up searching in the general vicinity. Maybe it's helpful?

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[reader2580]

If I do tear off, can I put down peel and stick/ice and water over whole porch roof and expect it to be Ok for a few weeks? I'd like to do full tear off, then build addition, then install roofing all at once.

I did peel and stick on the front half of my house roof. I left it that way for the entire winter with no leaks. (It was not my original plan.)

 

[billconner]

So I had decided on the nominal 1/2" CD - actually 15/32 - and building supply was out so they offered 5/8" - 19/32" - and I said OK. Since largest single.piece I'll install is about 3/4 of a sheet, hopefully I can handle it.

I'm quite certain code allows 15/32 on 16 o.c. framing here - with 60 psf snow load.

 

[chaddodson]

So I had decided on the nominal 1/2" CD - actually 15/32 - and building supply was out so they offered 5/8" - 19/32" - and I said OK. Since largest single.piece I'll install is about 3/4 of a sheet, hopefully I can handle it. I'm quite certain code allows 15/32 on 16 o.c. framing here - with 60 psf snow load.

Good on you for tackling this at 73 — that's impressive. For your setup (small hip roof, 60 PSF snow load, 16" OC spacing, and working solo), I'd say you're on the right track leaning toward ⅝" CDX. It gives you a bit more rigidity and holding power around valleys and hips — areas that tend to flex or get beat up during install. That said, ½" CDX is technically acceptable under most codes with 16" OC rafters and asphalt shingles, so if weight is becoming a challenge, you’d still be within spec using it. OSB is stronger in some lab tests (especially in shear), but it’s less forgiving to moisture — especially on an unheated porch where temperature swings can invite condensation. CDX will breathe a bit better and be easier to handle if you’re making lots of custom cuts. My vote: ⅝" CDX if you can manage the sheets solo, otherwise ½" will still get the job done with proper support and fasteners.

 

[billconner]

I had "investigated" the existing roof by using my phone camera through a hole in the ceiling. Thought existing framing was 16 oc but it is in fact 24 with 1/2" OSB. Not changing that. Addition is 16" oc and 5/8. Not too worried. 2/3 torn off and covered with ice and water shield. If it stays sunny I'll get rest done in next two days. Then new Azek fascia, followed by roof. Rest of trim and ceiling can be done in fall and colder weather.