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Srollins
Member
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# Posted: 19 Jul 2018 07:56pm
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Quick one gang, I found a good deal at Home Depot on 3/4" x 6" ship lap white pine , is there a problem using these for roof board sheathing?
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Borrego
Member
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# Posted: 19 Jul 2018 10:09pm
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I would rather use 2x6.....but maybe you could lay this down and then add ply on top......what kind of roofing are you using?
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ICC
Member
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# Posted: 19 Jul 2018 11:17pm - Edited by: ICC
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My question is, why? Why use boards instead of sheet goods?
Is it because you plan to make the underside visible to the room below? That then raises the question of, where does the insulation go? The insulation would be sheet XPS foam on top, then the finish fooring... shingles or metal?
Or is it because the shiplap is a super price? Cheaper than sheet goods? Boards were used for roofing before plywood came along, that.'s true. However those old roofs had the boards laid diagonally in order to provide racking resistance. Boards laid at 90 degrees across rafters provide little racking resistance, no matter how thick. If laying perpendicular to the rafters, then wider boards are better.
A shiplap board would have an advantage, over regular square edge boards, of better appearance, a less obvious gap between boards, if the underside is visible. But, IMO, the less rigid roof assembly, if boards are perpendicular to rafters, is a poor tradeoff.
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Srollins
Member
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# Posted: 20 Jul 2018 01:50pm
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Yes I'm going exposed appearance no insulation in the cabin and roof will be standing seam metal, I'm not apposed to adding a layer of plywood after the boards maybe 3/8" thick ply but the question is do I need to? I've never heard of anyone ever using ship lap on a roof , I just don't want any issues but at the same time want to take advantage of the cost affectivness.
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Eddy G
Member
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# Posted: 20 Jul 2018 01:57pm
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If your just using it for decking then why not?
Old cabins and homes used 3/4 (1 by's) for years before plywood sheathing was out there. If anything the ship lap would be an upgrade to the old fashioned 1x8's of yester year.
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Borrego
Member
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# Posted: 20 Jul 2018 06:06pm
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No insulation? If that's the case and you don't mind a less stable structure, then sure, go for it......as Eddy says, they used to do this back in the early days up till WW2
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Srollins
Member
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# Posted: 20 Jul 2018 06:31pm
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Thanks Eddy.
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Eddy G
Member
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# Posted: 22 Jul 2018 12:24pm
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Quoting: Borrego e and you don't mind a less stable structure, then sure, go for it
I wouldn't say it's any "less" stable maybe less convenient then sheet plywood. I hope it isn't two unstable, we own 3 houses right now one of them (a multi family investment property) was built in 1700. The roof deck is made up random sized boards (true 1") rough sawn boards...it's obviously had many new coverings since it was built and currently has asphalt shingles.
The house we live in was built in 1950 and has tongue and groove boards.
They're both still standing strong all these years latter.
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Fanman
Member
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# Posted: 23 Jul 2018 12:53pm
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Tongue and groove was used for many years, but I've never heard of shiplap being used for roof decking. I would be concerned as the overlap only supports the adjacent board in one direction.
That said, I've had no trouble with the same one way overlap in the T1-11 siding I used for my kitchen roof (rough side down)... though the T1-11 plywood is a lot stiffer than soft pine shiplap boards.
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Srollins
Member
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# Posted: 23 Jul 2018 03:21pm
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Understood fanman, my rafters are 16" on center. I too was concerned about the separation at the lap between the joist this stuff is dried so I dont think I will have a problem . but good point.
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socceronly
Member
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# Posted: 26 Jul 2018 12:25am
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Can you put down the shiplap or t&G and then put ply over top of it?
A no insulation mini cabin.
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