Illinois Roofing Practice Exam

How should double layers of rigid board insulation be installed in a low-slope roofing system?

1. Layers should be installed side by side

2. Layers should not have any spacing between them

3. Joints in the layer should be vertically staggered and offset from joints in the layer below

4. Double layers of insulation should not be used in low slope roofing systems

The correct answer is: Joints in the layer should be vertically staggered and offset from joints in the layer below

The correct approach to installing double layers of rigid board insulation in a low-slope roofing system is to have the joints in the upper layer vertically staggered and offset from the joints in the layer below. This method is crucial for enhancing the overall thermal performance and structural integrity of the roofing system. By staggering the joints, you minimize the chance of direct paths for thermal bridging, allowing for more effective insulation and a more uniform distribution of load across the roofing surface. This practice also functions to reduce wind uplift risks and potential water infiltration by creating a more robust and interconnected insulating layer. Other methods, such as placing the layers side by side or not allowing any spacing, do not achieve the same level of insulation effectiveness and could lead to weaknesses due to alignment that invites thermal loss or moisture issues. The suggestion that double layers should not be used at all in low-slope systems overlooks the fact that, when appropriately installed, they can provide significant benefits in energy efficiency and roof performance.