Answer a few quick questions and get an instant construction estimate for a legal, permitted backyard housing unit in Durham Region.
Includes foundation, framing, envelope, interior finishes, kitchen, bathroom, HVAC, utility connections, and Hernez Design permit fees. All costs in CAD, excl. HST.
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Gross interior floor area of the new detached unit (both levels combined, if two-storey), not the footprint of your lot.
Most Durham municipalities cap a one-storey garden suite around 60 m² (646 ft²) ground floor -- confirm your municipality's exact zoning by-law before finalizing size. A two-storey unit is measured by total floor area, not footprint.
Select levels, then a layout preset or your own room combination.
A two-storey suite adds an intermediate floor structure, an interior stair with guard/handrail, and additional structural engineering scope, and has more total exterior wall area to insulate and clad than a one-storey suite of the same floor area. This is offset in part by a smaller foundation and roof footprint; the net effect on your total depends on your specific size and layout.
Select rooms for your unit
Items marked "req." are included in every independent unit by code.
Please select a layout to continue.
Below-frost-line foundation is required in Durham Region (min. 1,200 mm per OBC). This is priced against your unit's footprint, and is one of the biggest cost drivers in the estimate.
Please select a foundation type to continue.
Select what applies. Sensible defaults are pre-selected if you're not sure.
A new detached garden suite always requires a full building permit and compliance with your municipality's specific zoning by-law (size, setbacks, height, parking). Development charge exemptions may apply under Ontario's More Homes Built Faster Act, 2022 (Bill 23, S.O. 2022, c. 21) -- confirm current status with your municipality. Hernez Design fees are included in the estimate below.
Total Estimated Cost
Hernez Design Fees (included in total)
Municipal permit fees and any development charges vary by municipality and are confirmed at permit submission. Structural engineering is a separate consultant, coordinated by Hernez Design.
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Want a more accurate estimate?
A Hernez Design site visit confirms your lot's zoning eligibility, soil/site conditions, and produces a permit-ready garden suite drawing set.
Ready for permit drawings?
Our BCIN-certified team prepares permit-ready garden suite drawing sets for Durham Region municipalities, plus structural coordination.
Preliminary Estimate - For Reference Only
This estimate is based on your inputs and assumes standard soil bearing capacity (confirmed by the geotechnical report included above), normal frost-depth footing requirements, existing grade, and that the lot meets applicable municipal zoning by-law limits for a garden suite (size, setbacks, height, parking, lot coverage). Actual costs may vary based on site conditions, tree preservation requirements, utility trenching distance, and finish selections. A contingency allowance is included for unforeseen conditions, but this remains a preliminary estimate, not a fixed-price quote. Excluded: legal survey and lot grading plan (priced separately if required), washer/dryer units, dishwasher, window coverings, and any conservation authority permit fees. Municipal permit fees and any development charge exemptions are confirmed at permit submission and vary by municipality. Contact Hernez Design Inc. for a detailed site assessment and permit drawing set.
Garden Suite - Legal Backyard Housing v1.6 by Hernez Design Inc. | All estimates in CAD, ex. HST