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Question DetailsAsked on 10/5/2014

I am replacing a low profile roof 2/12 but less than 3/12. Is it better to install a rolled roof or shingles?

If shingles are okay...which is better GAF timberline HD or GAF 3 tab 25 year sovereign shingles. This a 2 story house and the roof is not visible from the ground, so looks are not important. Also, do I need a ridge vent if there isn't an attic? The ceiling has fiberglass insulation and pine boards hiding the insulation between the rafters that are seen from below? The house is located on a river in Maryland with plenty of trees blocking the roof.

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Shingles versus roll asphalt roofing product - I would go with the shingles every time except on barns and sheds where the cost difference can control and minor leaks do not matter so much, because roll roofing lifts in wind and tears in wind and due to shrinkage and aging much easier than individual shingles - more like 5 o at most 10 year or so life as opposed to 20-35+ with good shingles.

However, for a less than 3:12 roof, especially in Maryland where you probably get a fair amount of rain and commonly gusty winds, I would use a seamed membrane roof or raised-seam metal, because that flat you are quite likely to get wind-blown rain and possibly wet snow-blocked water getting in under the shingles. If you do go with shingles for appearance look, I would go with full-coverage water shield underlayment rather than a semi-permeable roof wrap to provide a true secondary water barrier,because you are likely to need it.

If this was done right there should be an air gap (probably 2-4 inches) above the insulation, right under the roof sheathing, so any moisture that gets in there can escape rather than saturating the wood and insulation. It should also have had vapor barrier (visqueen) on the underside of the rafters, above the pine boards (which are presumably tongue and groove ?). If there is an air gap there, there should also be open (screened) eaves and eave baffles to keep the insulation (which should have been netted or continuously stapled) from slumping and blocking off the airflow under the roof surface. So yes - since that is an insulated airspace outside the building envelope, you should have eave and ridge venting. You can find some fairly lengthy discussions about attic and cathedral roofed insulation and venting issues in the Home > Roofing and Home > Insulation links in Browse Projects, at lower left.

Answered 5 years ago by LCD

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