Backfill
Backfill is the process of replacing and compacting soil or other material around foundations, retaining walls, and utility trenches after construction is complete.
Backfilling returns excavated soil (or imported fill material) around foundations after concrete has cured and waterproofing is applied. Proper backfilling requires compacting fill in lifts (layers) of 8-12 inches to prevent settling that can damage foundations or create drainage problems. Backfill material varies: native soil works if it's suitable, while clay soils may require imported granular fill for drainage. Backfilling must not damage waterproofing membranes or foundation walls—large rocks and mechanical equipment can crack or puncture protection systems.
Why It Matters
Poorly compacted backfill settles over time, creating depressions that collect water against foundations and erode soil. Settlement can pull away hardscaping like patios and sidewalks. Backfill timing matters: wait for concrete to gain adequate strength (typically 7-14 days) before applying lateral pressure from backfill. In Denver, proper backfill against foundations helps manage expansive clay soils—well-compacted granular backfill reduces soil pressure variations. Foundation drains must be protected during backfilling to maintain proper drainage function.
Best Practices
- Compact fill in 8-12 inch lifts using mechanical compactors
- Protect waterproofing and foundation drains during backfilling
- Use granular fill (not clay) in poor drainage soil
- Slope backfill away from foundation minimum 5%
- Keep fill below siding and brick ledges to prevent moisture wicking
- Water settle or mechanically compact to achieve 95% compaction
Related Terms
Grading
Grading is the process of shaping and leveling earth to establish proper drainage patterns, create building pads, and prepare sites for construction or landscaping.
Waterproofing
Waterproofing involves installing membranes, sealants, and drainage systems to prevent water from penetrating foundations, basements, showers, and other vulnerable areas.
Rebar (Reinforcing Bar)
Rebar is ribbed steel bar embedded in concrete to provide tensile reinforcement, preventing cracking and failure under tension, bending, and shear forces.