Just finished a major retaining wall project on our sloped Oakville lot. Posting the full breakdown for anyone researching this.
Our Project
- 45 linear feet of wall, approximately 4 feet high at the highest point
- Unilock Sienna tumbled block (interlocking concrete)
- Required a building permit (anything over 1 metre in our municipality)
- Engineer letter was required since we were over 1.2m at one section
Final Cost Breakdown
- Engineer letter: $850
- Building permit: $400
- Excavation and base prep: $3,200
- Block material (supplied by contractor): $5,400
- Drainage aggregate (clear stone) + geotextile: $1,100
- Labour (2-person crew, 3 days): $4,800
- Total: $15,750
That works out to $350/linear foot. For a 3-foot-high wall without engineer requirement, pricing would be closer to $200-$250/linear foot in this area.
Material Comparison
Interlocking block (what I used): $25-$45/sq ft of face area, clean modern look, 30-50 year life
Armour stone: $40-$80/sq ft, more natural look, very durable, needs equipment to place
Pressure-treated timber: $15-$30/sq ft but only 15-25 years in Ontario climate
Poured concrete: engineer-required for most applications, very durable
Critical Point: Drainage
Contractor explained that 80% of wall failures come from inadequate drainage behind the wall. Hydrostatic pressure destroys walls. Ours has 16 inches of clear stone behind it with a perforated pipe at the base discharging to daylight. Do not skip this.
Permit Reality
Check your local rules. Under 1m = often no permit needed. Over 1m = permit usually required. Over 1.2m = engineer drawings likely required.