Maximum slope for built-up roofs (tar & gravel)

[Zane Remenda]

Hi all,

Just wondering if anyone knows what the maximum slope is for a built-up roof (tar and gravel). I frequently see tar and gravel on flat roofs, but rarely on sloped roofs.

The roof was less than 8 years old and was missing a lot of gravel.

Thanks
Zane

[Jerry Peck]

Just wondering if anyone knows what the maximum slope is for a built-up roof (tar and gravel).

Depends on the type of asphalt used.

"Dead level" asphalt is what is used on flat roofs, when that asphalt heats up in the sun it tries to seek its own level, kinda like very slow moving water - but it is trying to seek 'level' and puddle there.

"Flat" asphalt can be used on roofs up to a 1/4:12 slope.

"Steep" asphalt can be used on, as I recall, roofs up to 3:12 slope. (I've read 2:12 and 3:12, so it may depend on the manufacturer?)

"Special steep" can be used on, as I recall, roofs up to 6:12 slope.