Completed a 280 sq ft single-storey rear addition on our 1978 Mississauga home. Kitchen expanded significantly and we added a proper mudroom. Documenting the process for others researching additions.
Project Scope
Extending the rear of the house 14 feet by 20 feet (280 sq ft). Scope included:
- New foundation (frost-protected shallow foundation)
- Framing, insulation (OBC-compliant: walls R-24, ceiling R-60)
- Windows (3 new)
- Roof tie-in to existing
- Kitchen expansion into new space (new island, extended cabinets)
- Mudroom with bench, cubbies, floor tile
Timeline
Application submitted: August 2025
Permit issued: October 2025 (9 weeks - longer than expected, Mississauga was backlogged)
Construction start: October 28, 2025
Substantial completion: February 14, 2026
Final inspection: March 5, 2026
Total from application to final: 7 months (5 months construction, 2 months permits)
Cost Breakdown
Architecture drawings: $4,800
Structural engineer: $2,200
Permit fees: $3,100
Foundation and framing: $38,000
Windows: $5,400
Roofing (new section + tie-in): $7,200
Insulation + drywall + tape: $8,600
Flooring (tile in mudroom, LVP in kitchen extension): $4,200
Kitchen modifications (cabinets, island, countertop additions): $12,800
Mudroom millwork: $6,400
Mechanical/electrical changes: $5,100
Painting: $2,400
Total: $100,200
Per sq ft: $358/sq ft - within the $300-$500 range I had budgeted for.
The Contingency Was Used
Budgeted $8,000 contingency. Used $5,200 of it on an unexpected sewer cleanout relocation that the site exposed.
Would do it again - the addition transformed how the house functions.