Why Roofs Have So Many Layers (And Other Residential Roofing Installation Questions)

If you are staring a new residential roofing installation in the proverbial face for the first time, you may have lots of questions about roofing. Looking at your estimates from various roofing contractors, you will see several types of roofing materials listed. These materials are necessary for creating an effective layered roof. However, you may be quite curious as to why the roof has to be layered at all. You may have some other residential roofing installation and construction questions, too. The answers are as follows. 

Each Layer of the Roof Serves a Purpose

Traditional roofing is layered roofing. Each layer serves a purpose. (Even metal roofing has one to two layers underneath, or it utilizes the current roof as its underlayers.)

There is a particle board layer that is nailed to the trusses, which are the framework of almost every residential home. Over the top of the particle board is a thin layer of material that will help protect the particle board and prevent it from absorbing moisture. Over the top of that, there is typically a layer of roofing "carpet," which is black and looks like a sponge.

Some roofing contractors may skip this "sponge" layer and go right to the rubber underlayment, but both layers do the same thing; they waterproof your roof. Finally, the shingles are nailed down, usually in strips over the top of the entire roof. The ridge poles and gutters are added last to help move water down and away from the roof and the foundation.

Why Metal Roofs Have Fewer Layers

Metal roofs need fewer layers because they do not experience water ingresses like traditional shingles can. In other words, metal roofs are naturally waterproof, which is why consumers love them. At the least, you may have a rubber layer over the particle board and under the metal roof, if you hire a contractor that tears off all of the old roof and starts fresh.

At most, you will have all of the old roof under the new metal roof, with possibly a layer of pitch/tar between to hold and secure the metal roof while the metal is bolted and secured to the several layers of old roof. However, most contractors recommend a complete tear-off of the old roof. If you are planning to install a metal roof as the metal roof and rubber underlay is all you really need for the next several decades.