Home Additions

Measure your lot and existing house. Check zoning bylaws for setbacks, lot coverage, and height limits. Most municipalities publish zoning maps and bylaws online. Calculate whether your proposed addition fits within zoning rules — if not, you'll need a Committee of Adjustment variance (adds 6-12 weeks and $1,000-$3,000). Verify services capacity: does your electrical panel have room for new circuits, or do you need a service upgrade? Is your HVAC system sized for the added square footage, or do you need a second system? Check for easements, rights-of-way, or building restrictions on your property (title search, $75-$150).

Hire an architect or designer to create floor plans, elevations, and sections showing the addition. The designer coordinates with a structural engineer who assesses existing foundation and framing capacity, designs new foundations and beams, and specifies tie-in details. Expect drawings showing: foundation plan (footings, walls, bearing points), framing plan (joists, beams, rafters), roof plan (tie-ins, valleys, flashing), wall sections (insulation, air barrier, cladding), electrical and plumbing rough-ins. Cost: $3,000-$8,000 for design, $1,500-$4,000 for structural engineering.

If your addition violates setbacks, lot coverage, or height limits, apply for a minor variance. Submit application with drawings, site plan, and fee ($1,000-$2,000). The Committee schedules a public hearing (6-10 weeks out). Neighbours within 60 meters are notified and can attend to support or object. The Committee grants or denies the variance based on four tests: Does the variance maintain the general intent of the zoning bylaw? Is it desirable for the development of the land? Is it minor in nature? Does it maintain the general intent of the official plan? Approval is common for reasonable requests, but neighbour opposition complicates things. Hire a land-use planner ($1,500-$3,000) if the request is contentious.

Submit drawings and structural letters to the municipal building department with permit application fee ($1,500-$4,000 depending on project value). Review takes 4-8 weeks. Common revision requests: structural detail clarifications, energy code compliance (R-values, window ratings), fire separation if the addition creates a second dwelling unit, egress window sizing. Some municipalities require HVAC drawings, plumbing isometric drawings, or energy models (EnerGuide). Once approved, you receive a building permit and can start construction.

Stake out the addition footprint (string lines and batter boards). Call Ontario One Call (1-800-400-2255) for utility locates — gas, hydro, water, sewer, telecom must be marked before digging. Excavate for footings — dig below frost line (4 feet / 1.2m in Ontario) to prevent frost heave. If building alongside existing foundation, dig carefully to avoid undermining it (excavate in short sections, brace if needed). If soils are poor (clay, fill, high water table), engineer may specify deeper footings, wider footings, or engineered fill (clear stone, compacted granular).

Build footing forms, install rebar (typically #4 or #5 bars, 18" spacing), pour concrete (3000-4000 PSI). Footings must cure 3-7 days before loading. Build foundation wall forms (ICF blocks, wood forms, or aluminum panels), install vertical rebar tied to footing rebar, pour walls. If tying to existing foundation, drill and epoxy rebar into old concrete before pouring. Install weeping tile around perimeter (4" perforated pipe in clear stone jacket, sloped to sump or daylight drain). Damp-proof exterior of foundation walls (rubberized asphalt or spray-on membrane). Inspection: footing inspection (before pour), foundation wall inspection (before backfill).

Install sill plates on foundation (pressure-treated 2x6, anchored with foundation bolts). Frame floor joists (typically 2x10 SPF at 16" O.C. — check engineer's span tables). Install subfloor (3/4" tongue-and-groove OSB or plywood, glued and screwed). Frame exterior walls (2x6 at 16" O.C. for R-20+ insulation) and interior partition walls (2x4 at 16" O.C.). Install headers over windows and doors (doubled 2x10 or LVL per engineer). Raise and brace walls. Frame roof — rafters or trusses per engineer's design. Tie into existing roof structure: sister new rafters to existing, install valley rafters, flash valleys with ice/water shield and metal flashing. Install roof sheathing (1/2" or 5/8" OSB). Inspection: framing inspection (critical — inspector checks structural connections, bearing points, beam sizes, roof tie-ins).

Install roofing underlayment (synthetic or ice/water shield in valleys and eaves), shingles, flashings (step flashing, valley flashing, kick-out flashing, chimney crickets). Install windows and exterior doors (rough opening must match window size — shim and flash per manufacturer specs). Install house wrap (Tyvek or similar) over sheathing, tape seams. Install siding to match existing (brick, vinyl, fiber cement, stucco) — matching brick coursing and mortar color is tricky; vinyl is easier. Seal the junction between old and new with flashing and caulk (butyl or polyurethane, not acrylic).

Run electrical: new circuits from main panel or sub-panel, outlets (12" above floor, 4' spacing on walls), switches, lights, smoke/CO alarms. Rough-in plumbing if adding bathroom or kitchen: drain lines (slope 1/4" per foot), vent stack (extends through roof or ties to existing vent), supply lines (PEX or copper, hot on left). Install HVAC: extend existing ductwork or add new system (furnace, AC, heat pump). Inspections: rough electrical (ESA), rough plumbing, rough HVAC/gas (TSSA if applicable).

Insulate exterior walls (R-20 minimum for 2x6 walls — batt or spray foam), ceiling/roof (R-50 minimum in Ontario — blown cellulose or spray foam). Spray foam at the junction between old and new structure (closed-cell, 2" minimum) to seal air leaks. Install vapour barrier (6-mil poly) on warm side of insulation in heated spaces, tape seams. Inspection: insulation inspection (before drywall).

Hang drywall (1/2" for walls, 5/8" for ceilings), tape and mud joints, sand smooth, prime and paint. Install flooring (hardwood, laminate, LVP, tile). Install interior doors, baseboards, casing, crown moulding. Connect electrical devices (outlets, switches, fixtures). Connect plumbing fixtures (sinks, toilets, showers). Install cabinets and countertops if adding kitchen or bathroom.

Book final inspections: building final (structure, envelope, fire separation if applicable), ESA final (electrical), plumbing final, HVAC/gas final. Install smoke and CO alarms (interconnected per OBC 9.10.18). Inspector will verify all code requirements, check handrails on stairs (34"-38" height, graspable profile), test GFCI outlets in kitchens/bathrooms, verify egress windows in bedrooms. Once all inspections pass, receive occupancy permit and move in.