Steep-Slope Roof Systems, Part 1
January 22, 2020
There are a variety of roof systems suitable for steep-slope roofs including asphalt shingles, metal roof panels, clay tile, concrete tile, slate (both “graduated” thickness and uniform thickness) as well as metal shingle systems. Our firm has installed all of the above systems, primarily on institutional facilities, including K–12, 2-year colleges, 4-year universities and colleges, and government buildings.
There are certain components which make for a successful roof replacement project on steep-slope systems:
- Minimum slope of 4:12 — a roof that rises 4 inches for every 12-inch run is important for redirecting water and snow. And the more precipitation your region receives, the greater the slope should be. For example: Buffalo, NY requires a minimum slope of 6:12 due to how much snow it receives, while here in the South, a minimum slope of 4:12 is generally sufficient. Roofs with less than 4:12 slope should receive single-ply, modified bitumen (torched or self-adhered), or elastomeric coating systems.
- Ventilation — proper ventilation allows any heat or moisture trapped in the upper part of the building to escape and prevents cold air from filtering in.
- Flashing — steep-slope systems may contain a variety of flashing conditions, and proper application of metal flashings is integral to the installation of a water-tight roof system.
- Underlayment — installation of the underlayment begins at the eave of the roof prior to installation of any flashing. Choosing the right type of underlayment depends on the roof system being installed and is the foundation of a well-designed, dependable roof.
Proper ventilation of roofs is key to having a roof with a long service life. Ventilation of steep-slope roof systems should include vented soffits, louvered dormers or gable ends, electric roof vents, and venting at ridges. Electric roof vents will engage when the attic temperature reaches a pre-set level. Venting at ridges is accomplished on wood decks by cutting a space of one to two inches on each side of the ridge. Then, specially-designed shingle ridge pieces are installed. The special ridge shingle has venting plastic adhered to the shingle’s underside, allowing heat to vent at the space in the plywood. Metal roof systems have specially-designed ridge vents provided by the manufacturer as part of the metal roof package.
Proper ventilation on steep-slope structures comprised of a metal deck substrate can be accomplished using a pattern of 1” x 6” or 2” x 6” pressure-treated lumber, followed by roof insulation fastened to the metal deck, between the pieces of lumber. A second series of lumber is then mechanically fastened over the insulation, followed by plywood, which serves as the substrate for the steep-slope roof system.
Whatever roof system is installed on a steep-slope roof structure, maintaining the required minimum slope ratio and ventilation is vital. Failure to properly ventilate the system will lead to premature failure of the new roof. In entry Steep-Slope Roof Systems Part 2 and Part 3, we will discuss the importance of the remaining two components of a successful roof replacement, flashing and underlayment.