By James R. Kirby
Self-storage buildings are a unique type. Many are single-story with large doors, and have sloped roofs that drain to gutters. Economical construction methods are used, with metal buildings and concrete masonry a frequent choice. Interior finishes are inexpensive or excluded, and exterior finishes include paints or coatings. This type of construction is extremely appropriate and an effective way to house peoples extra stuff.
Of course, storage facilities can consist of any building type and can be several stories tall. Existing buildings, such as warehouses, can be converted to self-storage. In addition, these buildings are not inhabited, so they already use minimal energy.
The roof is a considerable portion of a self-storage building envelope, which consists of the roof, walls and all penetrations, such as doors, windows and skylights. Many facilities include metal roofs, which is a practical choice because the metal panels also act as the roof deck. This one product serves two functions, reducing material and labor costs.
A roof's energy efficiency comes from roof color, the amount of insulation and the production of renewable energy. Rooftop energy production includes solar electricity (rooftop photovoltaic systems), solar thermal (rooftop hot-water systems) and wind energy. While the use of small-scale wind turbines is not common, solar electricity is an expanding business. Heres an overview of how these three key roofing componentscolor, insulation and renewable energycan help a self-storage facility be more energy-efficient.
Geography plays a role in the construction of self-storage buildings, certainly when it comes to roof design. The United States is divided into eight climate zones, and theyre primarily based on heating and cooling requirements. Climate zone one is the most southern and generally requires the most cooling and the least heating. Climate zone eight is the most northern and generally requires the most heating and the least cooling. There's more to it than that, but thats the gist of climate zones.
Roof design and construction affects the energy efficiency and interior comfort level of a self-storage facility. Roof color and the amount of insulation are key factors that help regulate the interior building temperature, especially in single-story, non-conditioned buildings, which is often the case for self-storage.
For a roof with minimal insulation, a dark color will absorb the suns energy, transferring the heat into the building. This is good during a Minnesota winter, but not very desirable for an Arizona summer. In contrast, a white- or light-colored roof will reflect the suns energy and less heat will be transferred into the building.
Roof color on minimally insulated buildings is a balancing act. In much of the country, its neither always hot or always cold, so perhaps the most practical color for a roof on a self-storage building is a medium color, like a gray or green. The roofing industry has many options that fit into this color scheme.
Roof coatings are often used to extend the life of an existing roof or can be used to change roof color. This not only upgrades the aesthetics, it can greatly improve the interior comfort for non-conditioned buildings. Choose the coating color wisely!
Requirements for roof insulation are outlined by building codes. New construction needs to meet the requirements of the International Energy Conservation Code or American Society of Heating, Refrigerating & Air-Conditioning Engineers (ASHRAE 90.1). Its smart to construct an energy-efficient building from the onset.
Heating is generally more expensive than cooling on a per-unit basis. As a rule of thumb, the requirements for insulation increase the further north a building is located. The code-required insulation amount increases as one moves from climate zone one upward, with the highest insulation amounts required in zone eight.
Semi-heated buildings require less insulation. The codes recognize that where less energy is used, less insulation is needed. For heated self-storage buildings, the required amount of insulation is the same as that for habitable buildings. Insulation is a one-time cost that helps regulate energy use for the life of the building. It's one of the few building materials that have real monetary payback. A well-insulated building uses less energy and has lower annual energy costs.
Ideally, roofs should have two layers of insulation with staggered joints, and metal fasteners should not penetrate through all layers of insulation. A metal fastener through the entire layer of insulation is a thermal bridge that will reduce the insulation's effectiveness. When using multiple layers, the top layers should be adhered to the lowest layer. Properly installing insulation improves the energy efficiency of the roof system.
For an existing building, there are many ways to upgrade the insulation and increase the building's thermal value, whether or not a new roof is required:
- Adding below-deck insulation
- For buildings with exposed roof decks, spray-applied foams and cellulose insulations
- Adding insulation and a membrane on an existing structural metal-panel system
- Spraying polyurethane foam on the top of an existing roof system
Rooftop Solar Panels
There are a few options for rooftop solar-energy production. The most common is solar panels on racks that are attached to the roof or roof structure or held in place with ballast. There are also solar panels that adhere to the roof surface. Membrane roofs (single-ply, asphaltic) and metal-panel roofs (steel, aluminum) can be retrofitted with solar panels if solar is not installed at the time of construction. There are also solar shingles that are installed on steep-sloped roofs. These are installed in place of traditional shingles or tiles. In any case, its important to ensure the roof structure is capable of supporting the additional load.
For self-storage buildings with low energy use, the idea of solar energy is financially promising. A relatively small investment in solar energy can mean the elimination of electricity bills. Of course, theres a lot to consider when determining if solar energy makes sense. Electricity costs, local and state incentives, and whether a building receives enough sunlight are important. However, single-story self-storage facilities likely have plenty of rooftop space and typically arent shaded by other buildings, so rooftop solar is worth considering.
Through roof color, insulation and solar energy, every roof has the opportunity to improve its energy efficiency and production, whether its an existing roof or part of a new construction project.
James R. Kirby is vice president of sustainability for the Center for Environmental Innovation in Roofing. For more information, visit www.roofingcenter.org . The Centers criteria for rooftop solar energy is available at www.roofingcenter.org/special/pv .