TB/02 – Strip Foundation, Cavity Wall and Ground-Bearing Slab

This strip foundation detail illustrates a typical junction between a concrete foundation, insulated masonry cavity wall and ground-bearing floor slab.

The drawing is intended for architectural designers, building professionals, contractors, developers and self-builders preparing a Building Regulations package or project specification.

For a plain-English introduction, see our related plain-English guide The wider structural context is set out in Approved Document A.

The detail shows:

• Typical 600 mm wide × 225 mm thick concrete strip foundation
• Minimum foundation depth and relationship to finished ground level
• Foundation blockwork and weak-mix cavity fill below ground
• External brickwork and Celcon Solar aircrete block inner leaf
• Partial-fill cavity wall insulation with a 50 mm clear cavity
• Damp-proof course and damp-proof membrane continuity
• Optional radon-barrier provision
• Cavity insulation extending below the floor slab
• Perimeter insulation and floor-edge sealing
• Compacted hardcore, blinding, insulation and concrete floor slab
• Typical foundation widths for different wall constructions
• Guidance covering stepped foundations and unsuitable ground
• Typical wall and floor thermal-performance targets
• SAP junction reference E5 with a calculated psi value of 0.070 W/m·K

The drawing includes coordinated specification notes covering foundation construction, concrete requirements, wall construction, mortar, wall ties, cavity control, insulation, moisture protection and ground-bearing floor construction.

What This Strip Foundation Detail Includes

• One downloadable PDF construction drawing
• A3 landscape sheet
• Drawn at 1:10 scale when printed at 100% on A3 paper
• Drawing reference: TB/02
• Detail title: Strip Foundation, Cavity Wall and Ground-Bearing Slab

Important Information

This is a standard construction detail intended to provide general design and specification guidance. It must be reviewed and adapted to suit the individual building, site conditions, ground conditions, structural loads, radon requirements, materials and applicable Building Regulations.

Foundation type, width and depth must be confirmed on site by Building Control and, where necessary, a suitably qualified structural engineer. The stated U-values and psi value apply only where the illustrated construction, dimensions, materials and installation standards are followed and should be confirmed through the project’s thermal assessment.

The drawing does not include project-specific structural calculations, ground investigation, drainage design, SAP assessment or Building Regulations approval. Purchasing or using the detail does not guarantee approval by Building Control.

The PDF is supplied for use by the purchaser on their own projects. It may not be resold, redistributed, shared as a standalone product or reproduced for commercial resale without written permission.