To glue roof boards?

Started by Bretttf, September 28, 2011, 10:32:46 AM

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Bretttf

I'm am about to put my roof sheathing boards on a shed roof.
I'm using 18mm (3/4") plywood and I plan to glue & screw it down but wondered about gluing the edges too?
Is it ok to put a run of glue along the edges of the boards too or should I leave a gap for movement?
Thanks


MountainDon

#1
I'm not sure about the glue; don't recall anyone doing that on a roof.

As for fastening the sheets to the rafters, depends on the screw if that is safe. Most screws that most DIY'ers grab are the common deck screw; gold zinc, etc. These are NOT good as their steel is hardened to keep the drive heads from stripping out easily. That makes them brittle. Shear forces, such as created by wind forces acting on the roof can readily shear those off. The building codes do NOT approve screws for that reason. Nails will bend before breaking. Using a proper size nail; 8D common, 2 1/2 x 0.131" diameter with 6" edge spacing and 12" field spacing (or less) is approved for normal wind areas. That's from IRC Table R602.3(1). There are footnotes that cover special situations. They should be read. Areas with tornadoes require more nails.

Just because something has been done and has not failed, doesn't mean it is good design.


rick91351

I would never glue.  I have had to change out sheeting before.  It would make it more difficult to get the new sheeting down correctly.  Why would you screw it down?  It would take longer and would not hold as well as nails.
Proverbs 24:3-5 Through wisdom is an house builded; an by understanding it is established.  4 And by knowledge shall the chambers be filled with all precious and pleasant riches.  5 A wise man is strong; yea, a man of knowledge increaseth strength.

CjAl

Use a ring shank nail if you feel you need the holding force of a screw. I also would never glue roof sheeting. Back when i did roofing id charge you double if i had to fight with that. Its very common to have to replace it. Especially from roofs put on by people who dont really know how.

Bretttf

Thanks for your responses guys, some points I had not considered.
My thinking was glue & screw would help keep the roof stiff, but if just nails are better then nails it is.
Time to glue & screw isn't an issue really, my garden cabin is a little hobby/project I'm doing at the moment.
Also I'm in England so Tornados aren't an issue thankfully


CjAl

Im.in huricane territory so i know the allur of glue it n screw it. I glue floor sheeting, wall stud, wall sheeting and pretty much anything else i can but nothing i have a good chance of needing to rip apart. I usually nail to minimum code ten add a few screws on top of that, mainly around edges.
metal roofing i will screw almost double around the edges and glue the seams. Huricane ike proved the benifit of that to me.

rocking23nf

I used tongue and groove 5/8ths sheets, and screwed them down.

Heavy as hell, but real sturdy also.

Bretttf

I think I'll use ring shank nails only to prevent any of them creeping out and potentially damaging my roof covering, which is going to be that EPDM Rubber.
Does the roof ply need to be exterior grade?
I can get free 3/4" (18mm metric) ply sheets that are approx 3' x 4' which I will use to sheath the interior but would that be good for the roof deck?
If not would any treatment make it ok to use seeing as it's free?

davidj

Note that a lot of ring shank (and galvanized) nails are thinner than the equivalent length smooth nails.  Be sure that they have the same thickness as 8d common nails (which may mean going 10d).

Undersized sheets won't be as strong.  You might be able to do something with metal straps to compensate but I'm not sure you could work out what without talking to an engineer (our neighbors put the sheets vertical, rather than the correct horizontal-and-overlapped, and they fixed it with straps).


considerations

"I can get free 3/4" (18mm metric) ply sheets that are approx 3' x 4' which I will use to sheath the interior but would that be good for the roof deck?"

Free is always tantalizing, however, the 8' span of sheeting on a roof covers twice as many rafter bays as a 4' piece and helps to stabilize and stiffen the roof structure.....somebody smarter than me told me so, and now, after seeing my cabin "shell" go from somewhat "flexible" to rock solid, I believe it. 

firefox

Since this is only a shed for practice, you can probably deviate from the norm, as long as you don't end up doing the same on something
that matters.
If the plywood is free and you can have as much as you want, I would
think you could just double up and have two layers such that the top layer ends up overlapping all the seams. Ofcourse there will be more cutting and nailing. If it is a small shed then I would think you could glue the two layers together as well as nail. Just be aware that if you ever have to repair it, you will have to treat it as one heavy massive and
awkard piece.

What the folks here are advising is good advice especially for something like a house, but if your just doing this for fun and you
understand the pitfalls, then just have fun with it.

This is just my opinion and should not be taken as good advice.
Bruce
Bruce & Robbie
MVPA 23824

firefox

Be aware, that if this isn't exterior plywood, it will tend to delaminate if it gets damp. You will need to put several coats of
some kind of waterproofing that will soak into the plywood.
I went to school near Dover and in London. It tends to get a wee bit
damp on your side of the pond.
Bruce
Bruce & Robbie
MVPA 23824

Bretttf

I could use that metal galvanised strap to help stiffen things up. We call it building band here.
I know I'm not following any code or normal practises fully but when things are free & with the costs of timber these days I'm just trying to do the very best I can with what I've got.
I have learned about framing, sheathing & other carpentry skills from this forum & I see you guys are a very knowledgeable bunch & also very resourceful.

I was thinking i might overlap the joints of the roof on the underside by using my 4' x 3' ply sheets as my ceiling boards too. That and the metal strapping would stiffen it up.
If not then I'll do 2 layers as you suggest because I can have as much as I like.
Its a kind of by product from the packaging we have at work
I've already had 35 sheets for my floor boards which I glued & screwed & that is very stiff with very little deflection.
Thanks for your help & ideas gents. I know I'm not strictly to any code so I do appreciate your suggestions to help resolve any issues I have