By: Rebecca Reilly
Roofing insulation varies based on the type of roof system. The goal of roof insulation is to prevent heat loss through the roof of a building. Many different types of insulation are available; insulation can be spray applied, installed in the form of a board or made of batt insulation. Board insulation is the most common type of insulation for flat roofs. The boards are either mechanically fastened to the roof deck or secured with adhesive. In some roof systems, the board insulation can be weighed down with gravel ballast or a paver system. The three most common types of board insulation are extruded polystyrene foam insulation, often referred to a blue board or “XPS” insulation, polyurethane and polyisocyanuate insulation, often referred to as “ISO.” The type of insulation in a roof system is often determined by the roof system manufacturer and the energy code requirements.
Vacuum insulated panels are a new type of board insulation on the market. These panels are meant to achieve high R-value with minimal thickness. Testing to understand the full potential of these panels is still being performed. A downside of using vacuum insulated panels is they cannot be cut or punctured. This makes it difficult for roofing contractors to install insulation around penetrations. Early planning is required so that insulation boards can be prefabricated to accommodate penetrations. The other difficultly with vacuum insulated panels is that they must be stored with care to prevent puncture. This can be especially tricky on a job site with limited storage capacity.
In New York City, flat roof systems are required to meet a minimum R-value of R-30. Typically, the greater the required R-value, the greater the thicknesses of insulation. Insulation manufacturers post R-value based on the expected value after it ages. Age causes the R-value of insulation boards to decrease. Insulation also loses R-value when it gets wet. For this reason, insulation must be stored in a dry environment and its packaging should remain in tack. If a board gets wet, it should be disposed of. Additionally, insulation can be damaged. For this reason, many roofing manufacturers require cover board be installed as protection over the insulation.
In some cases, insulation may not be necessary to meet energy code requirements when performing a roof replacement. If the space beneath the main roof is not conditioned, insulation is not mandated by code. Additionally, landmarked buildings are also often exempt from the energy code.