Bituminous Roof Minimum Slope

This 1 4 12 minimum roof slope requirement also applies to spray polyurethane foam spf roof.

Bituminous roof minimum slope.

Shingles of all types need to have a slope to function properly. 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. 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. All asphalt shingle roofs with a pitch of 4 12 or more have an underlayment of 15 lb.

On occasion codes will permit aggregate surfaced coal tar roofs down to 0 125 inches. Some people recommend not installing asphalt shingles on slopes below 5 12 but a skilled roofer may well be able to make this work. Asphalt shingles continue to be the most widely installed roof covering option in north america. 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.

They provide excellent weather resistance great value and now more than ever a tremendous range of beautiful designs and color blends. The idea is to provide positive drainage toward roof drains so there is no ponding water 48 hours after a rain storm. Asphalt felt paper that is tacked to the roof sheathing. This number corresponds to the number of inches of rise in a 12 foot run.

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. The minimum requirement is 2 12. There are differing opinions as to the minimum slope for a roof but the generally accepted minimum is 3 12.

Building elements a minimum design slope of 0 25 inches per foot is recommended for all membrane roof systems. Modified bitumen membrane roofs must have a design roof slope of 1 4 12 or greater 2 slope. That works out to about nine degrees if that works better for you. We can even help you find a professional to install it.

The short simple answer is 2 12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles. Experience the total owens corning roofing system and high quality roofing shingles. The 2 12 number is rise over run or two units of vertical for every 12 units horizontal. 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.

Owens corning produces high quality asphalt coating asphalt sealants and adhesives for asphalt shingles. The minimum roof slope allowed by code for any type of roof is in 12 applicable only to coal tar pitch roof systems.