Building Construction Handbook, Eighth Edition

Simple Raft Foundations ~ these can be used for lightly loaded

buildings on poor soils or where the top 450 to 600 mm of soil is

overlaying a poor quality substrata.

Typical Details ~

cavity insulation

external wall

floor screed

rigid insulation

damp-proof membrane

damp-proof course

damp-proof cavity

tray min. 150 mm

step

75 mm thick rolled

sand or similar

blinding

edge thickening to 150 mm

min. thick RC raft

(^300 225)
450 225
weep holes at 900 c/c
REINFORCED CONCRETE RAFT WITH EDGE THICKENING
REINFORCED CONCRETE RAFT WITH EDGE BEAM
floor screed
rigid insulation
cavity insulation
cavity tray
ground
level
external
wall
dpc
damp-proof membrane
steel fabric reinforcement
150 mm min. thick RC raft
forming ground floor slab
225
300 min.
750 minimum mass concrete
edge beam
225
compacted hardcore with
upper surface blinded with
50 mm coarse sand
Simple RC Raft Foundations