Cavity tray upstand height

150 mm

Cavity tray over an opening, abutment or cavity interruption

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

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The minimum vertical rise of a cavity tray from its bedding in the outer leaf to its termination in the inner leaf.

The tray steps up the cavity to the inner leaf with sealed stop ends, discharging through weep holes in the outer leaf.Original ProPlot drawing, not to scale. Geometry verified against Approved Document C, resistance to moisture.

Basis in regulation

Part C
Approved Document C
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How to check it on site

Photograph each tray before the next lift covers it. Confirm the tray rises at least 150 mm, is continuous, and has stop ends and weep holes at each end.

Common failure

Trays laid flat or with too little rise, missing stop ends, and weep holes omitted so water collects on the tray and tracks inwards.

Effective from 20 August 2026. 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