Controlled fill and the edge of a rebuild slab
What sits under the edge beam matters as much as the steel in it.
In short: At a Hills District pre-pour, controlled fill stopped short of the 1 m it must extend past the slab perimeter, and clay fill had started to slump at the edges.
Why fill comes up on rebuilds
Removing an older house and levelling a sloping block for a larger slab often means cut on one side and fill on the other.
The 1 m rule
Controlled fill that supports a slab or edge beam must extend at least 1 m beyond the building perimeter. Short of that, the edge zone has less support than the design assumed.
Clay fill slumping
On the same job, clay fill was subsiding away from the slab edges before the pour. That is a warning about support and compaction.
What else we check
Vapour barrier joints taped, loose soil cleared from the edges, bar chairs under the steel and re-entrant bars at internal corners.
After the pour it is too late
Fill and cover are hidden for the life of the house. Pre-pour is the only time to check.
Written by our local inspection team from work carried out in Castle Hill. Licensed building practitioners, NSW Fair Trading licence 366177C.
