Strap material compatibility and fixing height

150 mm

strap and fixing materials are compatible and that the lowest fixing is within 150mm of the strap's base.

Roof holding-down straps must be made of materials compatible with their fixings to prevent galvanic corrosion or other degradation. Additionally, the lowest fixing point for the strap into the supporting structure should be positioned within 150mm from the bottom of the strap to ensure effective load transfer.

Basis in regulation

Part A
Approved Document A
Read the source

How to check it on site

Verify that strap and fixing materials are compatible and that the lowest fixing is within 150mm of the strap's base.

Common failure

Incompatible materials leading to corrosion, or the lowest fixing being too high, reducing the strap's effective resistance to uplift forces.

Last updated 28 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.

Related dimensions at this stage

Minimum

Minimum eaves ventilation for pitched roofs

7,000 mm

For specific pitched roof constructions, a minimum continuous eaves ventilation opening of 7000 mm²/m is a common requirement

Minimum

Minimum strap dimensions for holding down

30 mm

A strap used for holding down purposes, particularly in roof structures, must have a minimum cross-section of 30mm x 2.5mm and be at least 1000mm long to effectively resist uplift forces.

Minimum

Equivalent ventilation areas for a cold roof

10,000 mm²/m at pitched eaves; 25,000 mm²/m at low level on flat or shallow roofs; 5,000 mm²/m at the ridge

Cold roof construction with the insulation at ceiling or deck level.

Minimum

Clear air gap above insulation in a cold flat or shallow roof

50 mm

Cold flat roofs and cold roofs pitched below 15 degrees.

Minimum

Ventilated batten space beneath a roof underlay

25 mm

Roofs designed with a ventilated space beneath the underlay, including counter-battened details.

Minimum

Minimum tile or slate width at a verge

150 mm

All verges on plain tiled, interlocking tiled and slated roofs.