TradeCalculator.co.uk
UK Cavity Tray Types & Specifications
Cavity tray DPC types, widths, weep hole spacing and installation requirements for UK cavity wall construction.
Cavity Tray Types
| Type | Application | Material | Notes |
|---|---|---|---|
| Horizontal tray | Above lintels, base of cavity | Polypropylene / lead composite | Must span full cavity width + both leaves |
| Stepped tray | Roof abutments (pitched roof to wall) | Pre-formed polypropylene | 75 mm steps to match brick coursing |
| Catchment tray | Below openings (sills) | Polypropylene | Collects water running down cavity |
| Caverntray | Ridge abutments, parapet walls | Pre-formed rigid plastic | For complex junction details |
| Perpend weep vent | Weep holes in outer leaf | Plastic insert | Max 450 mm centres along tray |
Tray Width Requirements
| Cavity Width (mm) | Min. Tray Width (mm) | Notes |
|---|---|---|
| 50 | ~300 | Must extend min. 100 mm into each leaf |
| 75 | ~325 | Standard domestic cavity |
| 100 | ~350 | Wide cavity with full-fill insulation |
| 150 | ~400 | Wide cavity with thick insulation |
Key Installation Rules
- Cavity trays must slope toward the outer leaf at a minimum fall of 1:12
- Stop ends must be fitted at each end of the tray to prevent water running off the sides
- Weep holes at maximum 450 mm centres (every other perpend in stretcher bond)
- Trays must project 5 mm beyond outer face or use weep vents
- Minimum 150 mm upstand on the inner leaf side
- Laps between tray sections: minimum 100 mm, sealed with compatible adhesive
Related Calculators
See the DPC Specifications for damp proof course types, or the UK Lintel Sizes for lintel specifications above openings. See also the Cavity Tray Calculator.
Next up: related pages
Frequently Asked Questions
Cavity trays are required wherever moisture could bridge the cavity and reach the inner leaf. Key locations include: above lintels (unless the lintel has an integral tray), at abutments where a roof meets a wall, at changes in cavity width, above meter boxes and other cavity closers, and at the base of walls where the cavity starts above DPC level. Approved Document C requires them at all these positions.
Horizontal trays run level across the wall, typically above lintels and at the base of cavities. Stepped trays follow the pitch of a roof where it abuts a wall (like a lead flashing stepped into mortar joints). Pre-formed stepped trays (e.g. Cavity Trays Ltd Type X) match standard brick coursing at 75 mm steps.
The outer edge of the cavity tray should project at least 5 mm beyond the outer face of the outer leaf to form a drip. This prevents water running back down the wall face. Some trays have a pre-formed drip edge. Where a projecting drip is not possible, weep holes with purpose-made weep vents are essential.
Weep holes should be provided at maximum 450 mm centres (every other perpend joint in standard brickwork). They can be open perpend joints (mortar left out of a vertical joint) or purpose-made weep vents/tubes. Weep holes must be provided at the lowest point of every cavity tray to allow collected moisture to drain outward.
Related Calculators
Was this calculator helpful?
Last updated: April 2026
Verified against UK standards 路 estimates only, confirm with your supplier.