Before attempting to replace your roof, it is essential to understand how to properly measure and calculate its pitch. In general, gable roofs have a low pitch while mansard roofs have a high one. In areas of high rainfall, the slope is generally high. In Papua New Guinea, longhouses feature steeply pitched roofs that sweep almost to the ground. Likewise, steeply pitched roofs are common in parts of Germany and Holland, where snowfall is heavy. However, in North America, the slope is at least six in twelve (1:2), with the minimum in Montreal being 30 degrees.
Asphalt shingles and roll roofing use asphalt as their base material. Asphalt shingles contain granules that increase water resistance. Another type of asphalt roofing is self-adhering. It meets ASTM D1970 standards to prevent water infiltration. Self-sealing shingles contain factory-applied adhesive that binds shingle courses together when exposed to heat. Roofing systems should also include back surfacing to prevent shingles from sticking to one another. Lastly, rafter construction directs water over a chimney, avoiding accumulation of ice and snow.
If your home is in good shape, but it has multiple layers of shingles, reroofing is not an option. Adding more layers can make the roof too heavy and may not fix the damage. Nevertheless, reroofing is an excellent solution for homes that don’t require a complete roof replacement. It requires less work and is less expensive than tearing off the old roof. If your roof is in good condition, reroofing is a great option.