The question of how many layers of shingles you can put on a roof depends on your local municipal building codes.
In the U.S., most states and municipalities allow two layers. The other factor that affects the number of allowable layers of shingle is the pitch of the roof such as a 4/12 pitch. Some municipalities allow roofs with steeper pitches to have three layers of shingles.
Factors to Consider
Normally, your professional roofer knows the local municipalities’ specifications.
However to better understand roof pitch, it is necessary to know what pitch sizes mean. For example, to know the amount of shingles needed for full tear off of shingles or a layer of shingles over an existing layer, pitch size is a factor.
Roofing pitch is defined as the slope at which the roof rises. For example, a 4/12
roof pitch simply means that the roof rises four inches for every 12 inches of depth. Most residential roofs are between 4/12 to 9/12 in roofing pitch.
Roofing pitch determines the safety and integrity of the building structure.
Types of Roofing Materials
Another factor is that understanding pitch also helps you to know the best types of materials for the roofing contractor project to be performed such as the one here on Meet RV.
Depending on the type of building, there are approximately eighteen types of
roofing materials. These include in commonly use order:
. Asphalt (3-Tab or architectural)
. Metal and metal clad with vinyl
Note that the type of roofing material affects cost. The average lifespan of an
asphalt roof in moderate climates is approximately 20 years. In regions where there is continuous humidity, high winds or rains, the wear and tear on roofing materials may decrease the lifespan of an asphalt roof. This is a factor to keep in mind when deciding to add a second layer of asphalt.
Slate, being a more expensive roofing material, lasts up to 100 or more years.
Metal roofing materials last about 50 years. A wood roof will last 30 to 40 years in normal climates. Concrete tile roofs last up to 50 years or more.
Rely on a Roofing Professional for Best Advice
Your professional roofer is your best guide to the lifespan of a second layer of
asphalt roofing material.
Also, the condition of the original layer of roofing material is a deciding factor in whether a second layer of roofing material should be considered or whether a full tear off is needed.
Normally, if your roofing underlying material is asphalt, asphalt will be the second layer of roofing of choice. This may also depend on local building codes.