ROOF SLOPE or PITCH : Rise/ Run
Conventional Slope: 4 in 12
Low Slope: 2 in 12 to 4 in 12
Flat: 0 in 12
The run in roof slope is usually expressed as 12.
Steep Roofs
Steep roofs are not watertight. They’re designed to shed water only. Flat roofs are meant to be waterproof.
VULNERABLE AREAS on Steep Roofs:
- wide chimneys near lower edges of the roof
- Chimneys in valleys
- Skylights
- Drains from upper roofs that discharge on lower roofs
- Changes in materials
- Equipment obstructing drainage
- Complicated flashing details
- Asymmetric valleys
- Patched areas
- Roofs that change slope
Ice Dam Potential
Occurs in areas where snow accumulates on roofs. Most common on the lower edges, party walls, chimneys. The northern slopes of the roof are the most vulnerable.
Possible solutions:
- Eave Protection
- Electric Heating Cables
- Upgrading Insulation and Ventilation
- Sealing attic floor to reduce leakage of warm moist air of house into attic
Multiple Layers
TIP: When counting the layers of roofing at flashing details. Be ATTENTIVE as many roofers usually cut the edgers of the under layer.
Metal drip edge flashing indicates wood workmanship but it is not a requirement.
Roof Type | Materials Used | Life Expectancy | Minimum Slope | Conditions | Multiple layers | $ |
Asphalt Shingles | Fiberglass Base, Asphalt & Surface Granules | 15-25 Years | 2 in 12 | Old, Damaged, Poor Installation, Fastener Problems, Hip and Ridge Shingles, Multiple Layers | 2 Max | |
Wood Shingles & Shakes | Cedar *
Redwood, Pine | 20 - 40 Years | 3 in 12 ; 6 in 12 more recommended | Old, Rot, Curling, Cupping and Splitting, Missing, Exposed Fasteners, Vulnerable Areas, Multiple Layers | You should not find multiple layers | |
Slate | Natural Stone Roofing Product | Depends on quality of slate. Durable overall. | 3 in 12 | Old/Damaged, Patches, Exposed Fasteners | ||
Clay Tile | Clay | Indefinite | Installation problems, cracked or broken, pitted or spalling, missing, fastener problems, flashing problems, underlying membrane problems, previous repairs | |||
Concrete Tile | Not confirmed Yet. However, some manufacturers provide a 50-year Warranty of the tiles. | Installation issues, cracked or broken, pitted or spalling tiles, missing or loose tiles, fastener problems, flashing problems, underlying membrane problems, previous repairs. | ||||
Fiber-Cement | Asbestos Cement, Mineral Cement, Cement Asbestos) | 30-50 years | 3 in 12 | Efflorescence, Cracked, Broken, Missing shingles. | ||
Metal Roofing | Copper, Stainless Steel or Aluminum | 25-50 Years | Rust, Fastener Failure, Loose or missing shingles or flashing, installation problems, dented, buckled roofing. | $ < Slate or Clay
$ > Asphalt | ||
Roll Roofing | Asphalt Based Material | 10 years or less | Cracked, Blistered, Buckling or Wrinkling , Open Seams, Loss of Granular Material, Fastener Problems, Cemenbed directly to sheathing, mechanical damage, downspout discharge, Multiple layers |
Wood Shingles/Shakes Roof : if more than 10-15% requires replacement, consider reroofing.
Slate Roof : Many other materials imitate slate (rubber, concrete, plastic). Be careful.
Clay and Slate Roofing: Fasteners and Flashing are most likely to fail than the clay/slate tiles.
Spanish Clay Tiles are commonly imitated by concrete tiles. Be careful.
Flashings
VALLEY FLASHINGS
Used when two different roof slopes come together to form a valley. They can be covered by the roofing material ( closed valley) or open and visible (open valley).
In open valleys, there should be at least 4-6 inches from the middle of the valley and it should widen as it goes down at a rate of 1/8 inch per foot. The widening is crucial since uniform width valleys are more prone to ice damming.
Closed valleys are common in asphalt shingle roofs. They are totally not recommended for wood roofs and could be used for clay, concrete or slate (but not common)
Chimney Flashings
Aluminum is not compatible with masonry mortar. Should not be used.
CRICKET OR SADDLE - peak that deflects water and snow around the chimney. Recommended if the chimney is 30 inches wide or more.
PIPE OR STACK FLASHINGS
ROOF/SIDEWALL FLASHINGS