A ridge roll is a flexible, wide strip fitted beneath the ridge tiles that closes the opening between the tiling and the ridge batten. The strip is perforated or made of an air-permeable material, so the ridge still works as a ventilation opening. Together with ridge clamps it forms what is known as a dry ridge system. The Dutch term is ondervorst.
Why a ridge roll
Traditionally, ridge tiles were bedded in mortar. That mortar cracks through temperature cycling and movement of the structure, after which water gets in and loose pieces come down. The ridge roll solves this:
- Weathertight — keeps rain and wind-driven snow out of the ridge
- Vermin-proof — birds, wasps and martens cannot get in
- Ventilating — the warm, moist air rising from the eaves can escape at the ridge
- Low maintenance — no mortar to be repointed after 15 years
How it is installed
- The ridge batten is mounted on ridge brackets and set to height so that the tiling meets it at the correct angle
- The ridge roll is unrolled and pressed down onto the tiles — usually with an aluminium or lead-free flexible edge that follows the profile of the tile
- The ridge tiles are laid and each one is mechanically fixed with a ridge clamp or screw to the ridge batten
Ridge rolls come in several forms: with a perforated membrane, with a pleated aluminium strip, or with a brush edge that follows the tile profile. They are supplied in rolls, in widths matched to the tile type.
Points to watch
- Ventilation must be continuous. A ridge roll only works if air can also enter at the eaves. If the eaves are sealed, the ridge does not ventilate
- Press the flexible edges well down into the tile profile; an unbonded edge lets wind-driven snow through
- At low pitches manufacturers often set additional conditions; check the minimum pitch for the chosen system
- Fix every ridge tile. The ridge carries the highest wind load on the roof
- Do not combine with mortar. A ridge roll plus bedded mortar simply seals the ventilation again
Related terms
- Ridge tile
- Ridge
- Dry ridge system
- Ridge batten
- Eaves tile
- Roof ventilation
- Bird comb
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.