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Question DetailsAsked on 8/15/2017

My dad wants me to leave old wood up on roof and place new boards right on top... not a good idea right ...

I have a back extension leaking for 10 yrs... around windows , in side paneling falling and rotted , this is what I can see... rafters are black and falling chips.... from constant water... I want to put new addition on next season, so just to make this not leak temporarily, got wood and all bought but my dad keeps saying to leave the old rot stuff... what ya think?

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Voted Best Answer

Here is a previoius similar question with answer - but relating to permanent installation -

For a case where you are going to replace the addition next year anyway, I would not be putting new wood on unless the roof cannot handle the winter snow load or is already collapsing - in which case I would just do spot repairs as needed - tear out small bad areas and put down cheapest OSB available and shingle over.

I have even seen cases where 3/8" plywood was put down OVER the shingles in the bad area (assuming the rafters will hold nails or screws) as sheathing reinforcement, then new roof water barrier (usually tarpaper as cheapest) put over it and underlapped with the surrounding shingles, then overshingle (including perimeter overlap) with the cheapest shingles or even strip shed granular shed roofing roll material done like an overlay shingle layer. Note if you do the plywood overlay thing you need to treat the area right above it like a roof edge and put in a starter row or two of shingles to bring the roof surface up to roughly planar, laid in under an overlapping existing row at the top, to provide runoff continuity and to prevent a low trough at the top edge of the plywood - make sure you have a decent continuous (though not necessarily perfectly flat) runoff path down the roof to prevent ponding at the patch.

Note that if patching (localized replacement of sheathing as opposed to overlay) because there is a chance (likely in your case) that water is running down the water barrier under the shingles, so at the patch you need to run its water barrier up UNDER the existing water barrier on the uphill and sides to catch any water running down over it so it does not dam up at the patch - the patch water barrier is then run out on TOP of the existing water barrier or shingles at the downhill side to drain - covered with shingles of course. Same sort of detail as around a skylight.

If the roof sheathing is not about to collapse you can just overlay with 70-90# shed roll roofing as a temporary fix, being sure to tuck it up one full shingle layer (so you need to reach up under with nail removal rybar under the shingles to loosen them and then with diagonal cutters reach under overlying layer and pull the nails on that row to get the new material in under) under decent condition shingles. Will typically (except in tornado/hurricane force winds) last 5-10 years and is about the cheapest and quickest solution other than an ugly tarp nailed down with wood strips. Available in a few unobtrusive granule colors - black, gray, dark brown, orangish brown, white in our area, varies by brand. For one season protection even non-granuled shed roll roofing (basically very heavy tarpaper) might well suffice, at about $0.50/SF including the nails. In windier areas use the more expensive round cap roofing nails which have about a 1" diameter metal washer on the nail to reduce the chance of pull-through in high winds - you will want plain metal or black probably, not the bright type used to nail on synthetic roofwrap where they are bright colored so workers can avoid catching their foot on them while walking around on the roof.

One note on the new addition - if you have chips coming off the rafters sounds like dryrot - so don't assume the roof is going to support you everywhere when working on it - test as you move around. And that type of damage is almost certainly going to need roof framing replacement during the rebuild. Also, the side paneling falling off means you should probably assume pretty much all the framing is shot - walls too, so you would have to strip out some interior finishes to see, but I would be counting (at this point) on the addition remodeling possibly being a total teardown and replace.

Bear in mind in the rebuild, while slightly rotted or just moldy wood can be cleaned up it is commonly not economic to do so, plus any damaged material you leave in place become a likely red flag for a home inspector at resale time - so generally best not to leave any questionable material in place and do the job right.

One other thought - especially if your parent(s) are elderly - sounds like there is almost certainly rot in the walls and ceiling too, which might be quite dangerous for them (especially black mold) - elderly people are more susceptible to lung problems from mold in the framing.

Answered 3 years ago by LCD

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