TMC Greater Simcoe

ADU Build Cost Calculator

Estimate the total all-in construction cost for a garden suite, coach house, or basement secondary suite. Sized off Southern Georgian Bay build-cost bands, with contingency, soft costs, and site services broken out.

Planning estimate, not a quote. Actual cost depends on your municipality, lot conditions, and builder. Full disclaimer.

Typical garden suite: 500-900 sqft

Soft costs and site services (override if you have quotes)
$

Design, permits, engineering, survey

$

Hydro, septic/sewer hookup, driveway

12-15% is typical for a fixed-price build

Planning estimate only, sized off Southern Georgian Bay build-cost bands. Get an actual quote from a builder before financing decisions are locked in.

Estimated total build cost

$226,600

That works out to about $302.13/sqft all-in, including contingency, soft costs, and site services.

The breakdown

Base construction cost (new detached build)
750 sqft × $240/sqft
$180,000.00
Contingency
12% of base construction cost
$21,600.00
Soft costs
Design, permits, engineering, survey
$10,000.00
Site services allowance
Hydro, septic/sewer hookup, driveway — highly site-specific
$15,000.00
Total$226,600.00

Once you know the build cost

The number this tool produces is the input the financing side actually needs. Run it through the ADU Financing Calculator to see how much of it you can actually borrow, or the Garden Suite Build vs. Status Quo calculator for the full net-wealth comparison over time.