Bituminous Roof Minimum Slope

All asphalt shingle roofs with a pitch of 4 12 or more have an underlayment of 15 lb.

Bituminous roof minimum slope.

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. 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. This means for every 12 horizontal units the roof must rise a minimum of one fourth vertical unit.

We can even help you find a professional to install it. The idea is to provide positive drainage toward roof drains so there is no ponding water 48 hours after a rain storm. Re cover with a second bituminous roof is generally permitted by building codes once surfacing gravel is removed spudded and wet areas replaced. They provide excellent weather resistance great value and now more than ever a tremendous range of beautiful designs and color blends.

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. There are differing opinions as to the minimum slope for a roof but the generally accepted minimum is 3 12. Some people recommend not installing asphalt shingles on slopes below 5 12 but a skilled roofer may well be able to make this work. What is the minimum pitch slope of an asphalt shingle roof.

Building elements a minimum design slope of 0 25 inches per foot is recommended for all membrane roof systems. The following table provides the minimum required allowable roof slope for each type of roofing material mentioned in the code. The 2 12 number is rise over run or two units of vertical for every 12 units horizontal. Modified bitumen roofing minimum roof slope roof pitch r905 11 1.

This 1 4 12 minimum roof slope requirement also applies to spray polyurethane foam spf roof. Asphalt felt paper that is tacked to the roof sheathing. Shingles of all types need to have a slope to function properly. Modified bitumen membrane roofs must have a design roof slope of 1 4 12 or greater 2 slope.

Owens corning produces high quality asphalt coating asphalt sealants and adhesives for asphalt shingles. Experience the total owens corning roofing system and high quality roofing shingles. Asphalt shingles continue to be the most widely installed roof covering option in north america. The minimum requirement is 2 12.

The short simple answer is 2 12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles. 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.