Weep hole spacing above a cavity tray

900 mm maximum centres, with at least two weep holes over every opening

Over lintels, cavity trays and at the base of the cavity

Every figure for this topic is on one page: Cavity trays and DPC: where are they needed and how high?

Read the full answer

Maximum spacing of weep holes provided to drain a cavity tray or the base of a cavity.

Basis in regulation

Part C
Approved Document C
Read the source

How to check it on site

Count weep holes over each opening as the outer leaf is built. They must sit in the course immediately above the tray, not one or two courses higher.

Common failure

Weep holes omitted over narrow openings, or formed above the tray so water collects and tracks inwards.

Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.

Related dimensions at this stage

Maximum

Wall tie spacing at reveals and movement joints

Additional ties at 300 mm vertical centres within 225 mm of the opening

Within 225 mm of an unbonded vertical edge — reveals, movement joints, wall ends

Maximum

Cavity wall tie vertical spacing

450 mm

vertical spacing of cavity wall ties does not exceed 450mm.

Maximum

Cavity wall tie horizontal spacing (partial-fill insulation)

600 mm

horizontal tie spacing for partial-fill insulated cavities does not exceed 600mm.

Maximum

Cavity wall tie horizontal spacing (full-fill insulation)

900 mm

For cavity walls incorporating full-fill insulation, wall ties must be placed at maximum 900mm horizontal centres

Maximum

Lowest fixing position for straps

150 mm

For any structural strap, the lowest fixing into the masonry or supporting structure must be positioned no more than 150mm from the bottom of the strap

Minimum

Chimney wall thickness and construction

100 mm

The minimum wall thickness for block, brick, or stone chimneys, excluding flue lining, is typically 100mm