Flat roof with pitch: to shingle or not to shingle?

Answered by Brett Kulina ~ September 12, 2012 ~ No Comments

Can you use shingles on a flat roof with a slight pitch?

Brett Kulina

If you want to install asphalt shingles on your home, then you must first determine the pitch of your home’s roof. Most building codes require a minimum of a 2 in 12 roof pitch if standard asphalt shingles are going to be installed.  Keep in mind that your local building codes may require an even steeper pitch, especially if your home is in a high snow area.  The problem with low-pitched roofs is that they cannot shed rainwater and snowmelt quickly enough to prevent the water from finding its way back under the roof shingles.

If you do not know the pitch of your home’s roof, then you can calculate this slope by using a small builder’s level and a tape measure.  Remember, a 2 in 12 roof pitch means that there is 2 inches of vertical rise for every 12 inches of horizontal run, likewise a 4 in 12 pitch would equate to 4 inches of rise for every 12 inches of run.  To determine your roof’s slope, hold the level so that one end of the tool rests on the roof while the other end is held in the air indicating a “level” position.  Starting from the point where the tool touches the roof, measure 12 inches horizontally along the tool and make a pencil mark.  Keeping the tool level, use a tape measure to measure the distance from the 12-inch pencil mark down to the roof, which will give you the approximate rise.

Before purchasing any roofing shingles, you should carefully read and understand the guidelines supplied by the shingle manufacturer, as the installation requirements vary between the various brands.  Some manufacturers may require a self-adhesive underlayment, such as Grace Ice and Water Shield, or a double layer of 30# roofing felt under your new shingles if your roof’s pitch is greater than a 2 in 12 but less than a 4 in 12. Likewise conditions around your roof’s eves and overhangs may also necessitate the installation of an adhesive underlayment to help prevent ice dams from building up under your roof shingles.

If you determine that your home’s roof is too flat for asphalt shingles, then you should consider using another type of roofing material, such as an EPDM rubber membrane or a rolled roofing product that is torched down with hot tar.  Once again, check your local building codes before making your final decision so that you can rest assured that you have chosen the appropriate type of roofing material for your home’s specific conditions.

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