No Plywood Under My Shingles!

Agree with Patchap. Weight from plywood is distributed well and is minimal. We do a lot of historic buildings with multiple layers over decks you wouldn’t believe, (mostly comp over wood over spaced sheathing). Adding plywood and one layer of shingles is a no brainer.

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Put 1/2 inch plywood on top. Buy the plywood and pay for installation labor :wink:

My roofer is insisting on removing the shiplap deck rather than sheeting over it. He says that it is inevitable that the plywood sheeting will start to lift and sent me pictures of prior jobs where that happened and because of that he is refusing to sheet over the shiplap deck saying that he cannot warranty the labor if we sheet over the lap deck. I raised the issue that the shiplap provides lateral support for the rafters and he claims that the plywood decking would provide the same lateral support? He says that they have removed lap and replaced with plywood sheeting in over 300 homes and it has never caused structural issues. I’m reluctant to let him go ahead with it but it seems like this may be an issue where there is just different schools of thought rather than a right or wrong - some say sheet over the lap deck, some say remove and sheet. Thoughts??

It’s not true. In the Pacific Northwest for years the highest volume of our work was shake conversion to comp. Shakes were always over spaced sheathing and NOBODY removed the spaced sheathing, we went over it with 1/2” sheathing. Never seen a problem when nailed properly.

But would it compromise the structure of the roof to remove the lap deck entirely?

Removing the lap decking and replacing with sheathing will do absolutely nothing to negatively affect the structure of your roof.

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nah,bullshit,just slap 7/16 osb ,hit rafters and good to go,how in the world properly attached osb would pop out,i dont understand physics behind it. please eli5 someone .ty.

The different school of thought is profit margin.

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I think going over makes the roofing nails have even more substance to grab onto.
And surely its original purpose of roofing nails not shooting into an air space.
The sheeting nails need to be ring shanked and shot properly into the trusses.
Honestly, this does take more skill than
If the original wood planks are removed.
Both are the right way to do it if nailed properly.
But it sounds like your potential contractor didnt have a roofer skilled enough to nail it right and he was just shooting into the bottom planks and not the trusses every time.

So he is protecting himself now against sloppy workmanship. Yes, it does cost him more to remove the wood and dispose it.
The wood would fill up a trash container or two all on its own without the roofing debris.

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He is not going to charge me any less for sheeting over the existing lap deck. He just doesn’t want to do it that way because of his past experience with lifting. So the bottom line is whether or not removing the existing shiplap deck would compromise the structure. I have 1 “no”, any one else have any thoughts on that??

Personally, i’d be looking for another roofer. Him suggesting leaving it will clause problems screams inexperience to me.

I strongly believe that plywood (or Osb) over spaced sheeting will give you the best of both worlds. Strength and holding power of solid wood, and the no gaps of 4x8 sheets. And he is pushing to give you a less quality alternative and charge you more to do so (you say he isn’t charging you more to remove it but I call b.s.).

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I’m just making sure what you are talking about. Shiplap, isn’t used in my area with wood shingles attached. Spaced 1X4’s are used. Normally spaced 3-4" apart. Smallest shiplap I’ve seen is 8" to 12". These are lapped over each other with no space between. Is this the decking that is on the home now?

1x6 planks. In some sections there is no gap between planks, in the majority there is less than an inch between planks, but in between some there is more than a full inch gap; some are broken, some are dry rotted, but about 75% is still solid.

Of course he is charging me more to remove the deck, but he won’t charge me any less to not remove and sheet over it which of course saves the cost labor, and trash disposal - as roof_lover pointed out, so yes you would think insisting on removing the decks accomplishes both aims: 1) avoiding the possibility of failing to properly secure the plywood sheeting over the lap deck, and 2) charging more for the extra cost of removal. But would removing the deck compromise the structure? Original 1946 timber frame roof - the rafters are stout and in very good shape. Would the process of removal cause damage to the structure? These are the questions I have. Right now I have 2 “no” - 1 from my contractor and 1 from Tileman. I’m just trying to make sure it’s done the right way so when I go to sell the house in the next few years it’s not a problem on a home inspection.

Since it’s a 3/4" solid deck now, sheeting over it would be the most logical choice. If you had plywood on it and wanted to sheet over it, 90% of roofers would tell you no. Understand you will be raising the roof another 1/2", so if you have flashing at a wall, you may have some details that need to be addressed. Drip edge will have to be checked to make sure it covers the original planks and the new decking. You’re looking at a minimum of 1-1/4" . If your fascia is below the planks any, you may have a gap. I’d check these issues. I would use at least a 2-1/2" nail, screw or ring shank and much like roof lover, hit the rafter. Once that nail is driven with a gun, it will sink into the rafter about 1-1/4". I would treat this like a redeck and I would field nail the horizontals. I’d also shop for a nail that has a ring or screw up the shank, close to the head.
I’ve removed plank decking before and ran into problems. When these homes were framed, the framer didn’t consider putting every rafter on any kind of consistent center, such as 16 or 24’s. They knew they were going to be putting up planks, so it wasn’t important. They might be an inch or half inch off. When you pull the planks off, plywood ends up getting wasted, because you cant stretch a 1/2". You may have lots of waste because of drops.
Anytime you place decking over another substrate, you could have a shingle fishmouth here and there. When the shingle nails don’t penetrate the deck, into open space, a minimum of 1/4" they could back out. It’s not likely, but with a good roofing labor warranty, I wouldn’t be too concerned. Not sure why the contractor doesn’t want to deduct some cost for a layover, but I’m not there to see it and I’m not going to second guess his idea.
side note. I didn’t realize this was a 14yr old bump post. Good job, digging up these old bones.

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I was very surprised when people started responding - last post 2006, ha!

Yeh, sheeting over the lap would require drip edge because the raise in the deck.

So if 90% of roofers wouldn’t sheet over an existing plywood deck, they would remove it and resheet, doesn’t that mean there is nothing wrong with removing the lap deck? And if your not going to second guess the idea of removal, are you saying it is ok?

I like this roofer - I’ve discussed all this with him and he has been cool, explains his rationale and why he doesn’t think there would be any problem structurally from removal, “I do 1000 roofs a year”.

I just want to do it the right way. But like most anything there are “10 ways to skin a cat.”

I have done a couple hundred sheet overs and dont recall any sheets popping
I tear off roofs my dad did 20 years ago and he used to nail them with roofing nails with minimal issues.
That said,as long as the plywood is rated for the span between rafters you wont hurt anything taking the old boards off.

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Full removal brings a lot more chance for accidents…
Danger is increased significantly.
Then sleeping at night knowing i threw away 2 trailer loads of perfectly good wood…

Just so you know, when i have done a full removal, i dont remove it all at one time.
Remove 5 feet across the bottom, sheet that
Tear another 5 feet across, sheet that.
This keeps the trusses straight , makes the job much safer and helps keep the structure intact while doing it.

There is nothing wrong with removing the old decking and it will not hurt the structural integrity of your building, especially if done incrementally how roof lover mentioned to keep trusses secured. There is nothing wrong with going over existing decking. You ARE paying more for it though no matter how it is presented to you, and it is unnecessary. No way is someone doing all that extra work for free.