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Question DetailsAsked on 7/6/2017

cand I re replace rafters with plyboard on roof

our house is 50 years old. rood is 8 years old but leaks. 4 different companies have repaired it but still leaks.
can plyboard replace rafters?

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1 Answer


I am stumped - if it leaks there is a problem with the roofing itself (very unusual) or with the person doing the repairs (or 4 people in this case), or you have a flashing leak or leaking vent pipe (probably most common cause). But replacing the rafters - how will that solve your problem ?

or is this perhaps a terminology misunderstanding - the rafters are the usually 2x4 or 2x6 (sometimes larger) "beams" which run "down" the roof from the ridge of the roof to the eaves and commonly overhang the eaves by 2-4 feet to provide the soffit area and provide a roof overhang to shield the house from direct rain impact in all but blowing rain. They are the supporting members that carry the roof load and cannot be eliminated unless you replace them with wood or rarely (in two story or less residences) metal roof trusses (which still have top chord members which serve the same purpose and look about the same).

Maybe you are talking about old planking used roof decking - the materials lying across the top of the rafters, which supports and the shingles are fastened into ? If so, then yes - that can easily (though of course means doing a full reroof in the process) be torn off and replaced with plywood sheathing - sheathing thickness determined by the design roof loading and commonly 15/32" thick these days (nominal 1/2") though wider than 24" rafter spacing or very high code design wind or snow/ice loadings can up that requirement. My preference - 3/4" pressure treated (for insect and rot resistance) exterior plywood, as in my mind OSB/waferboard and similar particle board type products are junk and asking for trouble in case you ever get a leak because they swell and fall apart when wet - though most contractors will propose them to keep their price down. (Even saw one house the other day being reroofed with - literally - sawdust board - just sawmill sawdust impregnated with glue (which was not waterproof - fell apart in a minute or two in a can of water), is basically a sheet form of MDF.

Sounds like you need a good roofer in the first place, and one who has (or you rent one for $50-100, if inclined to walk on roofs) a thermal infrared camera, which you/they use to identify where the wet areas within a day or so of when it has leaked again (so wet spots are still wet), to tie down where the uphill limit of the wet areas in the sheathing is. This assuming it is not evident from underneath. Best time to do the thermal IR scan is morning or late evening, when there is a big difference between attic and roof temperature - the wet zones change temperature slower, so will generally show up as cooler in the morning when the roof is already heating up from the sun, or warmer in the evening as they retain the day's heat in the wet material as the roof is cooling off. Works well on all but fully ventilated/double layer roofs (which have a continuous airspace under the roofing) or in tile roofs where the thickness of the tile masks out and distributes the underlying heat flow. The leaks will be near (but commonly a bit below due to wicking) the top or highest point of the wet spots.

Answered 3 years ago by LCD

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