What is the ridge of a roof?

The ridge is the highest horizontal line of a pitched roof where the two sloping roof surfaces meet. The ridge board is the structural timber at the apex of the roof frame into which the rafters are fixed. Ridge tiles or a ventilated ridge system cap the junction at the top of the tile or slate courses to shed water and - in modern construction - ventilate the roof void.

What is a ridge board?

A ridge board is the horizontal timber running along the apex of a pitched roof into which the tops of the common rafters are fixed on either side. It is not a structural load-bearing member in the same way as a purlin - its purpose is to provide a fixing point and keep the opposing rafters aligned.

What are ridge tiles bedded in?

Traditional ridge tiles are bedded in a mortar mix and pointed at the joints. However, mortar bedding cracks over time as the roof moves. Modern best practice uses a dry-fix or mechanically fixed ventilated ridge system, which is more durable, eliminates repointing, and provides the roof ventilation outlet required by Approved Document F.

How do you ventilate a roof at the ridge?

Ridge ventilation is achieved using a purpose-made ventilated ridge tile or a dry-fix ridge system with a continuous ventilation strip running along the apex. This provides the high-level outlet required for cross-ventilation of a cold roof void, working in combination with eaves ventilation inlets.

Ridge - Construction Glossary

Definition

The ridge is the highest horizontal line of a pitched roof, where the two sloping surfaces meet at the apex. It has two distinct elements: the ridge board - the structural timber running along the apex into which the rafter tops are fixed - and the ridge tiles or dry-fix ridge system that caps the junction at the top of the tiling to shed water and ventilate the roof void.

In practice

The ridge board is not a load-bearing structural member - it provides a fixing point and keeps opposing rafters aligned rather than carrying load. Rafters are cut and fixed to it at the correct pitch angle. In cut roof construction the ridge board runs the full length of the roof; in trussed rafter construction the ridge is formed by the top chord of each truss.

Traditional ridge tiles are half-round or angular clay or concrete units bedded in mortar. Mortar bedding inevitably cracks and lifts as the roof moves seasonally, requiring periodic repointing. Modern best practice is a dry-fix mechanically secured ventilated ridge system - more durable, maintenance-free, and providing the mandatory high-level ventilation outlet for the roof void. When re-roofing, switching to dry-fix ridge is strongly recommended.

Building Regulations

Relevant PartsPart A (structure), Part F (ventilation)

Ridge ventilation requiredYes - high-level outlet for cold roof cross-ventilation

Approved DocumentsAD A, AD F

Approved Document F requires that cold roof voids are cross-ventilated between eaves-level inlets and a high-level outlet at or near the ridge. A ventilated ridge tile or dry-fix system satisfies this requirement. Mortar-bedded ridge tiles do not provide ventilation unless a separate ridge vent tile is incorporated.

Full Building Regulations guidance

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Roof Pitch & Rafter Calculator Roof Tile Calculator

Ridge

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