by Mark Gregory, CGC, CCC
Architects, specifiers, and roofing contractors play an important role when working with a building owner to design a commercial structure that protects occupants from the outside environment. The roof is an essential part of the building’s design phase, and planning its construction from the beginning can be extremely complicated. Producing the best design possible at an affordable price is of the utmost importance for everyone involved.
To select, detail, and specify the most appropriate roof system for a project, both the commercial roofing contractors and the design team should have past experience with several of the available material options, as well as an understanding of the various roof assembly materials, system options, and roof design considerations.
Utilizing a collaborative approach from the first phase of the design process is imperative to identifying all of the criteria and required performance characteristics early. For example, during the initial inspection, a roofing contractor will determine what roofing systems the client has used in the past and whether that system meets the needs of an upcoming project. The design phase should involve clear communication of the designer’s overall concept with specifications and drawings that can then be executed by a professional roofing contractor.
Components to consider
When selecting a roof, there are many different options available, including thermoplastic, ethylene propylene diene terpolymer (EPDM), metal, and vegetated assemblies. While each of these systems has its own advantages and disadvantages, it is vital the chosen assembly fits the building’s usage, climate or location, energy and environmental performance, and warranty.
Building usage
A primary consideration during the design phase is the building’s intended use. The occupancy, insulation requirements, and maintenance schedule must be fleshed out. For example, a warehouse would require a different roof system compared to an educational institution or hospital. Also, the aesthetics would be more important for a school or healthcare facility and the design of the roofing system may need to include certain textures and colors for brand identity or curb appeal.
Climate
The aspects of the climate that most affect the design of the roof system include expected precipitation (amount and type), temperature, and wind. A building in a dry climate does not need the same type of roof as a building subjected to heavy rains. (Annual amount of snow accumulation must also be considered.) Snow can drift and collect in corners, topping flashings and leaking into the facility. Hail can puncture a roof system, so in regions prone to this weather, a roof that can withstand the harsh elements is needed.
If the geographical location of the building experiences large temperature swings between summer and winter, a roof system that will expand and contract with thermal movement is a good choice. Climate obviously affects the amount of insulation required. Predominately hot areas should consider a reflective roof system to save on cooling costs. Savings in cold climates depend on several factors, including cost of heating energy compared with cooling, the slope of the roof, insulation, and size of the building.
In areas prone to high winds, identifying uplift requirements is important. Any location with wind gusts higher than gale force (i.e. up to 100 km/h [62 mph]) should take wind speeds into consideration. Even a 64-km/h (40-mph) wind can cause a poorly attached roof to detach from the building.
Efficiency
A building’s roof was once just thought to be a way to keep the inside of a building dry, but the impact a roof can have on energy consumption is now better understood. The roof system is one of the largest surfaces of the building envelope; it has a significant impact on the energy-efficient operations of the finished project.
Every roofing system has a predetermined rate of reflectivity and emissivity. These characteristics help ascertain whether the membrane reflects or absorbs solar energy. The greater the reflectivity, the less energy is absorbed, helping cut the transfer of radiant energy. The lower rate of reflectivity, the greater the rate of energy absorption and the transfer of radiant energy.
Factors such as roof membrane color, increased insulation thickness, and different insulation types should be considered. After developing multiple scenarios, a well-thought-out decision can be made concerning which option makes the most sense and produces the best return on investment (ROI).
There are many programs offering the ability to develop different options for improving the energy efficiency of the roof system, including the Florida Power and Light Rebate Program and the Energy Star Roofing Program. Collaborating with professional commercial roofing contractors is ideal, as they have in-depth knowledge and can provide feedback for architects, specifiers, and building owners regarding how the choice of the roofing system affects energy performance.
