What This Requirement Covers
Approved Document D (Toxic Substances) has a narrow scope: it addresses the requirement that cavity insulation materials used in masonry cavity walls must not release fumes that are toxic or harmful to the health of building occupants. In practice, the requirement applies to urea-formaldehyde (UF) foam injected into cavity walls.
Key Requirements
Regulation D1
Building Regulation D1 requires that where insulating material is injected into the cavity in a cavity wall, reasonable precautions must be taken to prevent the permeation of toxic fumes into any occupied part of the building.
Application
- The requirement applies specifically to injected cavity wall insulation in existing cavity walls
- The most common material of concern is urea-formaldehyde (UF) foam, which can release formaldehyde gas during and after injection
- Other injected materials (polystyrene beads, mineral wool blown fibre) do not typically produce toxic fumes and are less affected by this requirement
Precautions for UF Foam
- The inner leaf of the cavity wall must be substantially complete (i.e., without cracks, gaps, or missing mortar joints that would allow fumes to pass through)
- If the inner leaf is of fair-faced brickwork or blockwork without plaster, it must be checked for completeness and any gaps must be sealed
- The installer must ensure that the foam does not enter the building through gaps around window frames, service penetrations, or other openings
- The British Board of Agrement (BBA) issues certificates for cavity wall insulation products, including conditions of use
Current Practice
- UF foam has largely been superseded by other cavity fill materials (expanded polystyrene beads, mineral wool, and polyurethane foam) that do not produce formaldehyde
- Where UF foam is still used, it must be installed by a BBA-certified installer following the specific conditions of the BBA certificate
- The Cavity Insulation Guarantee Agency (CIGA) provides 25-year guarantees for cavity wall insulation installations
Practical Compliance Tips
- If specifying cavity wall insulation, choose a product with a current BBA certificate
- Ensure the installer is registered with an appropriate guarantee scheme (CIGA or equivalent)
- Before injection, the installer should survey the inner leaf for gaps, cracks, and missing mortar that could allow fume penetration
- Retain the installation certificate and guarantee for the property records
- If occupants report chemical odours after cavity wall insulation, ventilate the property and contact the installer and CIGA
- Building Control should be notified of cavity wall insulation work under Part D; some competent person schemes cover this notification