Bituminous Roof Minimum Slope

The minimum requirement is 2 12.

Bituminous roof minimum slope.

Some people recommend not installing asphalt shingles on slopes below 5 12 but a skilled roofer may well be able to make this work. Modified bitumen membrane roofs must have a design roof slope of 1 4 12 or greater 2 slope. The minimum roof slope allowed by code for any type of roof is in 12 applicable only to coal tar pitch roof systems. On occasion codes will permit aggregate surfaced coal tar roofs down to 0 125 inches.

They provide excellent weather resistance great value and now more than ever a tremendous range of beautiful designs and color blends. Building elements a minimum design slope of 0 25 inches per foot is recommended for all membrane roof systems. What is the minimum pitch slope of an asphalt shingle roof. Let owens corning help you determine when it is time for a new roof and then let us help you choose the shingles for your roof that are right for you.

The idea is to provide positive drainage toward roof drains so there is no ponding water 48 hours after a rain storm. This number corresponds to the number of inches of rise in a 12 foot run. The minimum slope for a flat roof is 1 4 per foot or 1 4 12 but some owners or insurance companies require a minimum slope of 1 2 per foot. The short simple answer is 2 12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles.

Asphalt shingles continue to be the most widely installed roof covering option in north america. Modified bitumen roofing minimum roof slope roof pitch r905 11 1. Asphalt felt paper that is tacked to the roof sheathing. Re cover with a second bituminous roof is generally permitted by building codes once surfacing gravel is removed spudded and wet areas replaced.

The following table provides the minimum required allowable roof slope for each type of roofing material mentioned in the code. That works out to about nine degrees if that works better for you. This means for every 12 horizontal units the roof must rise a minimum of one fourth vertical unit. Shingles of all types need to have a slope to function properly.

For example the international building code 2018 edition ibc 2018 prescribes a 1 4 12 minimum roof slope for asphalt built up polymer modified bitumen thermoset and thermoplastic single ply and liquid applied membranes in new construction. Experience the total owens corning roofing system and high quality roofing shingles. But shingle roofing is not watertight in the sense that standing water or wind driven water on a low slope roof can work its way up between the laps which is the reason for the minimum 2 12 slope. Owens corning produces high quality asphalt coating asphalt sealants and adhesives for asphalt shingles.

All asphalt shingle roofs with a pitch of 4 12 or more have an underlayment of 15 lb. The 2 12 number is rise over run or two units of vertical for every 12 units horizontal.