In flat roof construction, which layer is typically located above the thermal insulation?

In flat roof construction, the layer that is typically located above the thermal insulation is the roof membrane. The roof membrane serves as a primary waterproofing layer that prevents moisture ingress, thereby protecting the underlying insulation and other components of the roofing system from water damage. It is usually made from materials that have high resistance to water and weathering, such as EPDM, TPO, or PVC.

Having the roof membrane positioned above the thermal insulation helps to shield the insulation from direct exposure to the elements, which could compromise its performance. Additionally, it ensures that the insulation remains dry, thereby maintaining its thermal performance over time.

In comparison to the other options, the vapour barrier is installed below the insulation to limit moisture penetration and prevent condensation within the insulation layer. The roof deck is the structural component that supports the entire roof assembly and is located beneath the thermal insulation. The wear course, often associated with built-up roofing systems, may be applied on the top of the roof membrane for added durability and protection from mechanical damage but is not the layer immediately above the thermal insulation. Thus, the roof membrane is the most appropriate answer as it directly fulfills the role of providing a waterproof barrier while being situated above the insulation layer.