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Stopping The Rot at Eaves Level: Best Practice for Vapour-Permeable Roofing Underlays
By Niall Crosson
Tuesday 21st October 2025
Best Practice for Vapour-Permeable Roofing Underlays
When it comes to the long-term performance of a pitched roof, one of the most vulnerable areas is the eaves. This is where roofing membranes/underlays are most exposed to sunlight and moisture, and where the most common failure point is. Over time, that seemingly small detail can lead to major problems, including timber rot, moisture ingress and expensive repairs.
Blog author
Niall Crosson
Technical Director (BTech, MEngSc, MIEI, CEPHC)
Niall is the Technical Director for Ecological Building Systems and was also the company’s first employee. Niall holds a first class honours degree as a Bachelor of Technology and a Masters in Eng.Sc. Niall is a certified Passivhaus Consultant and has provided technical guidance on many award winning low energy projects in Ireland and the UK, and has authored or co-authored several chapters in both the Passivhaus Handbook and the Passivhaus Designers Manual. Niall is also on the board of directors of the Irish Green Building Council and provides guidance on several national standards committees. Along with this, Niall has contributed to several construction publications including The Journal of the RIAI.