Advances in roof technology offer opportunities to increase energy efficiency.
When it comes time to replace a roof, a facility manager shouldn’t automatically replace it in kind or make decisions based only on the lowest bid scores. The new roof system should be selected based on its ability to improve other aspects of a building’s resilience, sustainability, wellness strategies and long term durability. Choosing a roof system based on the overall functional objectives of the building provides ongoing value over the life of the structure.
The durability of the roofing materials is always an important consideration. Roofing materials have changed significantly in the past 30 years due to labor shortages, environmental regulations and insurance requirements. These changes mainly affected the material fastening methods. Proper roof selection now includes not only determining the best roof membrane system, but also determining the correct fastening method for the building.
Since the roof is one of the largest exterior components, it is also one of the most expensive that will require maintenance for the life of the building. Therefore, the selection of a roof system should not be based primarily on an initial low cost. Ultimate cost considerations should be based on the long-term performance of a roofing system, which should include limited annual maintenance requirements and affordable repair methods. Initial cost savings are deferred when the roof system has a shortened service life or requires significant annual maintenance and repair costs.
In addition to these basic requirements, facility managers can use the new roof system to upgrade their system in two other areas: energy efficiency and the wellbeing of the residents.
Improving energy efficiency
Energy efficient roof systems and sustainability have developed significantly over the past two decades. Due to regulations and assessments of the facility managers, these topics have top priority when purchasing decisions for roofs. Recent advances in materials, methods, and design of system components have highlighted energy efficiency. Roof systems have an impact on energy efficiency through thermal capacity, emissivity and reflectivity.
The biggest deterrent to energy efficiency in the building envelope is heat loss from the exterior. Since roofs are often the largest external component, implementing methods to reduce (or eliminate) heat loss from the roof system is the best way to contribute to the overall performance of the building. Roof systems can eliminate heat losses by applying suitable thermal insulation and membranes with sufficient emission rates.
In roof systems, the thermal capacity is achieved by installing an insulation system with high values for long-term thermal resistance (LTTR). In commercial low pitch roof systems, the insulation is a rigid sheet that is placed over the deck. High LTTR insulation reduces heat loss in the winter months, thereby lowering heating costs through the use of a lower energy capacity.
The adoption of the ANSI / ASHRAE 189.1 standard for the planning of high-performance green buildings according to the International Building Code in 2007 provided the required LTTR values for the insulation of all commercial roof systems with low inclines for the first time. The LTTR values are based on the thickness of the insulation and are defined in the standard based on the geographic region of the building. This standard has increased the insulation thickness required in the roof system.
The emissivity prevents heat from leaving the building by undermining its exit as it rises to the roof level. In the case of roof systems, this is achieved through a combination of insulation and membrane material. The LEED emissivity for a roofing membrane is at least 0.90, based on ASTM E408.
Energy efficiency can also be achieved through adequate reflectivity of the surface of the membrane material. Unlike emissivity, which prevents heat from leaving the building, reflectivity prevents outside heat (from the sun) from entering the building. Reflective roof surfaces can be achieved with light-colored membranes or by adding coatings or other reflective surface materials. Reflective surface roofs can lower surface temperature by up to 30 percent and extend the life of some membrane systems by reducing expansion and contraction. Studies have shown that reflective surfaces cool the building in the summer, reducing the use of air conditioning, reducing cooling costs and energy capacity.
Proper roof construction should include the required insulation thickness, proper fastening methods, and required fastening rates. It would also be advisable to do dew point calculations for appropriate emission rates to remove condensation in the isolation system. When applying a coating, ensure that it is compatible with the membrane and that all prep requirements are properly met. The application should meet the manufacturer’s requirements.