Foundation Detail: Cavity Wall with Beam-and-block Floor

This detail focuses on a standard trench foundation, where a cavity wall meets the floor (in this case a suspended beam-and-block floor, although this could easily be a ground-bearing slab or otherwise). The depth and width of the actual poured conrete foundation has been left off, as this varies greatly depending on the soil conditions. An AutoCAD drawing of this detail (in 2004 format) can be downloaded at the end of the article.


  1. 102mm clay facing brickwork (standard size of a brick in UK)
  2. 100mm cavity with partial fill insulation held back by wall ties between blockwork and brickwork
  3. 140mm concrete blockwork
  4. Plaster finish, painted as required
  5. Perpend plastic weep hole (allows any water in cavity to drain away)
  6. Cavity tray (acting as damp-proof course)
  7. 102mm caly facing brickwork suitable for below ground use
  8. 100mm concrete blockwork
  9. Weak mortar fill to cavity base (to prevent outer leaf of wall falling inwards under pressure from ground
  10. Poured concrete foundation
  11. Void
  12. 150mm concrete beam and block floor
  13. 1200 gauge polythene sheet (damp-proof membrane)
  14. 75mm rigid insulation board (to prevent heat loss through earth)
  15. 75mm cement sand screed with underfloor heating pipes
  16. 100 x 19mm softwood skirting board


Source: professional architect's detail used on real-life project

Additional downloadable files

foundation - cavity wall and beam-and-block floor.dwg
Submitted by Nick Howlett82 Articles
Published on Tuesday 1 September 2009View Profile