Applying Shingles on Steep Slopes and Mansard Roofs

Technical Bulletin #23

Current as of June 2019

With the many different styles of architectural design, steep slope (including mansard) roof shingle applications are not uncommon. While it is always important to follow the manufacturer’s installation instructions, it is even more so on steep slopes. Often, manufacturers have enhanced application instructions when shingles are applied to steep slopes.

While a standard steep slope will normally require a 4 nail application per shingle, in part due to the effectiveness of the factory-applied self-sealing adhesives on shingles, very steep slopes that meet or exceed 15:12 (50 degrees), like mansard style roofs, will require more care. In that case, one should meet the following recommendations:

  • Secure the shingle to the roof using an enhanced fastening pattern. Often, this is a 6 nail pattern as opposed to the traditional 4 nail pattern*.
  • Seal down each shingle, at the time of application, with  three 1”diameter (approximately the size and thickness of a quarter) spots of asphalt plastic cement placed 1” above the bottom edge of the shingle and equally spaced across the shingle*.

Fasteners should be placed according to the shingle manufacturer’s installation instructions. On very steep slope roofs, correct placement of nails on laminated (two-piece) shingles is even more critical as the nails will penetrate both shingle layers when placed correctly. If the nails are placed too high on the shingle, it is possible that, over time, the bottom layer, which will be held in place only by the factory applied adhesive, will delaminate and slide off the roof.

*Check the shingle manufacturer’s installation instructions to know the correct pattern, type and quantity of nails and adhesive.

The information contained in this bulletin is for general education and is not intended to replace advice from a qualified contractor or direction on usage/installation from the manufacturer. Consumers should be aware of the safety hazards associated with work on roofs and, before doing so themselves, should consider following CASMA s advice of using qualified contractors. This bulletin may be reproduced with permission on condition that it be reproduced in whole, unedited, with attribution of copyright to CASMA.