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Question DetailsAsked on 5/22/2016

new osb sheeting on roof but a dip between two rafters. Roofer says it is from settling. I think can be fixed.

27 yr. old house. Old roof had lots of leaks. Tore off old roof and am having new OSB installed but a high rafter makes the new roof look bowed at ridge 5 feet from Eve. Roofer put on shingles 1/2 of house and the rolling high point looks bad. He says it's from the house settling and will be fine. I think he should pull of the OSB sheet where the dip is and scab in some kind of boards to level the ridge. Who is right. Or is there a better way?

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A single high rafter should not be from house settling - sounds like an original problem to me - probably a miscut or mismeasure.

I assume you KNOW this is a rafter problem- not just a case of too tight a sheathing fit (no gap at joints) or debris on the rafter preventing the sheathing from laying down right - should be obvious if you look in the attic, because in those cases there would be a gap between rafter and OSB.

Ideally they should have noticed that not later than when they laid down the OSB - but before nailing. Certainly YOUR call on whether it looks bad enough to need repair. Several ways to fix this, but most would have to be done BEFORE shingling.

1) remove shingles and water barrier and build up the low point with shim 2x stripwood, as you say - before OSB went on - and making sure OSB fasteners are long enough for correct holding power figuring the shim thickness as having no holding power - so probably requires 1/2-1" longer screws or nails for the OSB being fastened in that area. Should also make sure there are enough nails through the OSB to ensure the stripwood is hold in place too.

2) go into the attic and drive in closely spaced wide shims (to avoid distinct bulges) between OSB and rafter, then use longer screws/nails through the OSB into the rafter to ensure correct holding strength - but again, would have to be done BEFORE roofwrap/shingles are on or remove and replace them.

3) best way would have been resetting the high rafter so it sat correctly - best done before OSB went on, but may be able to use a keyhole saw or sawzall or such and drills (depending on working clearance) to correct the setting height if due to an incorrect notch depth at a ridgepole. I have even done corrections like this (TEDIOUS !!!) with a die grinder (commercial size dremel tool) nibbling away the excess material to correct the setting location. Or if due to high setting of a joist hanger, with correct shoring with temporary supports the rafter could be freed from the hanger and either the hanger nails pulled and the hanger lowered, or the hanger abandoned (flattened out) and the rafter lowered and a new proper type joist hanger put in to hold the rafter at the correct height. Could be done with the roof already on assuming adequate room in the attic to work (or possibly by removing ridge vent in that area and working from the top, depending on type of fix - like if just shortening the rafter a bit to correct length), though a bit of risk (depending on how high it is) of putting a wrinkle in the shingles as it is lowered that might have to be taken out with selective nail/staple removal and trimming a few shingles to length to remove the wrinkle. Both these solutions probably, and the following one certainly should be at the direction of a Structural Engineer to be sure the work is done correctly and that all support is not removed from that section of the roof during the work.

4) Again would have to be done with the shingles off, but localized removal and then using a close clearance saw like a toekick saw or hand rip saw, cut a proper thickness strip of wood from the top of the high rafter (which would also have to cut through any nails left there), renail the sheathing over that area, repair the water barrier, and replace the shingles. Then repair the rafter (with structural engineer design) - usually either by sistering 2x4's or even paired glued and nailed 1x4's with close pattern nailing on both sides of the trimmed rafter (must be 2x4 material if only nailed), or by putting in nailed and glued 2x2's on both sides along the top to beef it up and a 2x4 flat on the bottom glued and nailed properly to turn it into an I beam. Commonly, with only a small amount of rafter removal (say an inch or less) just a longitudinal 2x4 pattern nailed flat under the rafter is adequate - depends on snow load and amount of depth cut away and original rafter depth. Another method for short runs of trimming is gluing and nailing plywood strips or pattern nailing repair metal strapping on both sides of the rafter - but because these come no more than 8 feet long in general, only useful if the reduced section length is about 4 feet or less in length, as a rafter repair cannot generally be made up of several pieces - usually has to be continuous for the entire repair length.

On the repair - you said a high rafter is the problem - shimming up the OSB on both sides would then leave a ramped ridge effect which would not reduce the height of the out-of-plane section of the roof, so I doubt that would look acceptable - if obvious now, would probably look like an extremely flat gabled section of roof, and if near the ridge more likely to stand out against the skyline at the ridge. Lowering or cutting down the high rafter is probably the only visually acceptable way to correct this - and if hgih enough to be real obvious, the trimmed rafter should be reinforced, not just left with a reduced depth - especially if in snow country.

Contractor would have to give you prices depending on how he wants to do it (including engineer cost if applicable so you are looking at total cost either way). Unfortunately, because this was (presumably) a pre-existing condition, unless blatantly obvious in the original roofing as a bulge (which he should have mentioned to you) or required to be fixed as part of the contract, unless correction was in his scope of work then the cost of tearoff of that section and correcting the issue would probably rightly be at YOUR cost.

Hard to estimate the cost - but I would expect lowering the rafter without roofing removal, or minor removal only to remove any wrinkle that forms, likely in the $500-1000 range. Any solution with tearoff of that section and repair from above more likely $1000-1500 range, I would guess.

I would guess his preference would be tearoff that area and fix from the top, especially if a roofer only and not a framing carpenter (which you may need for the rafter repair). My personal preference, if there is work room and the rafter hanger or length can be adjusted to solve the problem would be to try to fix it from inside the attic - or through ridge vent slot if just a matter of trimming the rafter end so it is a bit shorter so it will drop down where it is supposed to be. But then my background includes a LOT of remedial jobs for issues like this, so fixing it iin place is less scary to me than to many contractors, who generally tend to think of tear out and replace with new rather than in-place repair solutions.

Answered 3 years ago by LCD



This is Brendon M. in Member Care.

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Brendon M.

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Answered 3 years ago by Member Services

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