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Question DetailsAsked on 4/29/2013

when should decking be replaced ditinh roof replacement

The entire roof was replaced with new shingles and underlayment

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1 Answer


Assuming you mean "when should decking be replaced during roof replacement - bit of a hand placement slip during typing there, it looks like.

When you say "when should decking be replaced, I assume you mean the roof sheathing - the plywood (or heaven forbid, particle board) that underlies the felt and shingles.

The answer is it should never need replacement (at least not in 100 years or more). If you attic is properly sealed to prevent household moisture from getting in, is well ventilated (eave vents and ridge or endwall vents, and the roofing is not let go to the point of disintegration before replacement (every 20-30 years, typically for normal shingles), then the sheathing and roof joists/trusses should stay in good condition indefinitely. Look at all the 200 year old barns with original roof structure and sheating, as long as the roof coering was maintained. Of course, barns tend to have steeper slopes, whcih helps a lot with preventing water from backing up under the shingles.

Now the caveats - if you are in a very cold climate where just natural air moisture that accumulates in the attic frosts up on the undersides of the sheathing in the winter, an area with very hot or very humid summers, your bathroom and kitchen vents leak into the attic area rather than venting flawlessly to the outside, etc - then the sheathing will eventually begin to delaminate and get bulges in it, and eventually rot. Letting leaves and other tree droppings accumulate on your roof will also very quickly promote shingle and sheathing decay. Also, if you are in a snowy area and have any low roof vents or experience ice damming or eave icing, then unless your vent caulking and ice and water shield works perfectly, eventually you will get small water leaks in those areas that cause local sheathing deterioration. In that case, practically speaking - at least some sheets of sheathing along the outer edge and in the vent areas will probably require replacement every 2nd or 3th reroofing, typically a couple to maybe 8 or 10 sheets.

One way to reduce this is, if you are in a part of the country where snow sits on your roof for a significant period of time, mandate an 8 foot strip of ice and water shield along the downhill edges of the roof and in every valley rather than the 3-6 feet most codes require, and demand ice and water shield overlayment OVER the felt around bathroom and kitchen vents and tailing out on TOP of the shingles about 3-4 feet downhill of the vent, so it gets any leakage back on the roof surface rather than letting it run all the way down the roof under the shingles. If you have a tight grouping of vents more or less in one uphill/downhill stripe (which is common in cold area houses, where all piping and vents are kept in one tight interior zone of the house), then I recommend a solid stripe of ice end water shield from ridge to eave, and extending 3 feet each side of the outermost vents, typically for a total width of about 10 feet. That provides much better water protection in the zone, where snowmelt from the vents promotes local ice damming and water backup under the shingles. This protection can eliminate sheathing damage, and extend your roof life 5 years or more, as this is the zone (along with valleys) that usually deteroriates first.

Answered 7 years ago by LCD

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