Ridging and fishmouths on flat roofs

Roofing · Modified Bitumen · printed page 24 (PDF page 25)

Original page Sign in to save

Book index entries

Fish Mouths on Flat Roofs Fish Mouths Ridging Ridging on Flat Roofs Built-up Roofing

Text in the illustration

roofing felt
ridges and wrinkles may be due to lack of asphalt, moisture, felt slippage or differential thermal expansion
fishmouths are open at the edge of the felt ply potentially allowing direct water access

Generated explanation

The illustration shows a roofing felt ply on a flat roof with two elongated raised ridges or wrinkles in its surface. The annotation identifies lack of asphalt, moisture, felt slippage, or differential thermal expansion as possible causes. A separate raised fold extends to the edge of the felt ply, forming an open fishmouth. This edge opening potentially allows water direct access beneath the ply.