A roof system includes all of the components in a successful roof, from waterproofing membranes to coverage surfaces, such as gravel. Most owners and property managers recognize the importance of this complete roofing investment that protects their buildings and its contents from water damage. Although a manufacturer and/or contractor's warranty may have been acquired, the owner is ultimately responsible for proper roof care and maintenance. Roofing contractors have become a valuable resource in helping these owners manage their assets and offer owners routine scheduled roof inspections and maintenance programs.
A good roof system requires proper design, quality materials, quality application, and bi-annual maintenance to perform successfully.
We’ve included definitions and explanations for the components of a roofing system, so that when it’s discussed, you’ll know what’s meant.
The Roof System
The National Roofing Contractors Association (NRCA) classifies roofs into two major categories: Low-slope roofs and steep-slope roofs. There is no such thing as a "flat roof" because if a roof was completely flat, the water would never drain off of it.
Low-Slope Roofing or Commercial Roofing includes waterproof or impermeable roof types that are built on a slope less than 14 degrees:
Primary Components of low slope roofs:
- Decks & Substrates (the first layer)
- Membranes (the second layer)
- Surfaces (the third layer)
Decks & Substrates
Decks and substrates provide the foundation for your roof system. It must be durable and strong.
- Wood – plank or plywood used primarily in housing and light commercial
- Steel – most commonly used in commercial, manufacturing and distribution facilities
- Light Weight Concrete – poured over metal pan
- Concrete – gypsum plank, Tectum (acoustical), and double “T’s”
Substrates, which attach the roofing membrane to the building:
- Fiberglass Base Sheets, insulation(s), and vapor barriers.
- Base sheet – nailed or mopped down. They are the most commonly used in wood decks (residential).
- Insulation – fire resistance, energy conservation, recovery boards screwed down with an exact pattern. Insulation is most commonly used in commercial facilities.
Membranes help protect your building from moisture and other weather. There are a number of different kinds of membranes, and we can recommend which one is best for your project.
Rubber / Thermoset (Single-ply)
EPDM (ethylene propylene diene monomer) is an elastic synthetic rubber. Because it is fully cured, seams are formed using contact adhesives or tapes. Seams and flashings require careful attention. EPDM is lightweight, flexible and usually black. It is available reinforced and non-reinforced, fire retardant and non-fire retardant, and varies in thickness from 45 mil to 90 mil.
TPO, PVC, CSPE (Single-ply)
These thermoplastic membranes are flexible, reinforced, heat-welded membranes. Most thermoplastics are reinforced and fire retardant. Selection of the most appropriate membrane requires knowledge of the specific conditions on each roof, including the building environment and physical stresses to which each individual roof is exposed, and the performance of each membrane. Thermoplastic membranes are lightweight, energy efficient and aesthetically pleasing. They adapt well to unusual shaped buildings and to buildings that experience substantial movement. High production rates, greater chemical and fat resistance and great tensile and tear strengths make thermoplastics a fantastic choice for nearly any low slope roof.
Built-up roofing (BUR) (tar & gravel) and Modified Bitumen roofing
This roofing membrane is built up by alternating layers of asphalt or coal tar saturated felts or fiberglass mat roofing plies. These systems can be durable and long lasting when carefully installed in multiple layers with quality bitumen, felts and flashings. Built-up roofing (BUR) can be used in both new construction projects and on existing buildings. BUR systems have low flexibility and are only appropriate on roof decks with minimal movement or where appropriate expansion joints are provided. BUR systems require periodic maintenance to maximize their service life. In some installations, BUR can be designed to be more durable and resistant to casual roof traffic.
Modified bitumen roofing
This roofing membrane is manufactured in a consistent, controlled environment and is generally coated or covered with mineral granules. Modified bitumen systems are more flexible than BUR systems, yet share many of the advantages, including good resistance to roof traffic. They are a good choice as a replacement for a BUR system or on certain high traffic roofs.
Surfaces (Gravel, Coatings, Granules and No Surfacing)
The purpose of surfacing is to provide weatherproofing, protect the foam from UV exposure, provide protection from mechanical damage and assist with fire resistance nature of the roof system. There are several different ways to surface a roof.
- Gravel is inexpensive, covers well, is ultraviolet resistant, and performs well in standing water.
- Coatings (spray, roller or brush applied) are easily maintained, offer view of membrane for ease of repair, and oxidize in standing water.
- Granules are broadcast into a coating to provide increased surface durability and aesthetic value.
- Pavers can turn a roof into a patio.
- No surfacing at all is also an option, since many roofing assemblies are designed to operate without the addition of surfacing.