At what slope does the NRCA recommend using a weatherproof membrane under slate roofing?

The NRCA (National Roofing Contractors Association) recommends using a weatherproof membrane under slate roofing for slopes greater than 4:12. This guidance is based on the understanding that, at lower slopes, there is a higher risk of water penetration, especially during heavy rains or wind-driven conditions. The membrane serves as an additional barrier to protect the underlying structure from moisture infiltration, which can lead to significant damage over time.

At slopes of 4:12 or lower, relying solely on the slate roofing system might not provide sufficient protection against water intrusion, which is why the incorporation of a weatherproof membrane is critical in these scenarios. For slopes above this threshold, while a membrane may still provide an added safeguard, the risks associated with water damage are reduced, making it less of a necessity. Thus, the recommendation to use a weatherproof membrane specifically for slopes greater than 4:12 reflects both best practices in roofing and a proactive approach to safeguarding building integrity.