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Design to a Target Budget: How to Draw a House That Costs What You Said It Would
Plans and design Costs From a builder
Design to a Target Budget: How to Draw a House That Costs What You Said It Would
The usual order is draw, price, cry, redraw. The order that works is number, levers, draw, price-check, draw again. It is not complicated, and almost nobody does it.
Short version: Start with the all-in number you can actually spend. Subtract the lot, servicing, design, permits, HST and contingency to get the construction budget. Hand that number to the designer with the cost levers (shape, size, storeys, foundation, ceilings and glass, mechanical, finish level) and have a builder price the sketch before it becomes a permit set. Budget first, drawing second, every time.
Step one: the number nobody wants to say out loud
The all-in number is what you can spend on the whole project without lying to yourself: savings plus the mortgage you have been approved for plus any sale proceeds, minus a cushion for life. Then take out everything that is not the house: the lot, closing costs, servicing (well, septic, hydro, driveway), design and engineering fees, permits and development charges, HST net of the rebate, and a contingency of 10 to 20 percent. What is left is the construction budget, and it is smaller than people expect.
The custom home building calculator does this arithmetic backwards for you, and the hidden costs list is the list of things to subtract.
Step two: translate the budget into a house
Divide the construction budget by a realistic cost per square foot for your finish level and region, and you have a ceiling on size, which is the first thing to tell the designer. Cost per square foot explains why that number lies, so use it as a ceiling, not a target: a complicated 2,000 square foot house costs what a simple 2,400 does. Then decide the big-ticket choices before any drawing: storeys, foundation type and walkout, wall system, heating system, and a finish level you can name (builder-grade, mid, high). Those five decisions set 80 percent of the price.
Step three: give the designer the levers, not just the number
Designers design to what they are told. Tell them this:
- The construction budget and the maximum square footage
- A rectangle-first rule: every jog and roof plane has to earn its place
- The storeys, foundation and wall system you have chosen
- Nine-foot ceilings on the main floor, and where, if anywhere, you want more
- A window budget: the big glass goes where the view is and the overhang can protect it
- The mechanical room location and the heating system
- The finish level, and which three rooms get the money (usually kitchen, main bath, entry)
The seven decisions that set the cost is the long version of each lever.
Step four: price the sketch before the permit set
The cheapest moment to find out a design is over budget is when it is a sketch. Give the preliminary plan and elevations to a builder for a budget price, with the finish level and the mechanical choices written on it. A good builder prices a sketch within a range in a week. If it comes back 15 percent over, the designer trims; if it comes back 40 percent over, you go back to step two. Only when the sketch prices inside the budget does the designer produce the permit set, which is where the design fees are really spent.
Builders will do this because the sketch that prices well is the one they get to build. Builder first, then designer is the same argument from the other side.
Step five: allowances and the selections schedule
Once the price is set, every item you have not chosen is an allowance, and allowances are where designed-to-budget houses drift. Shop them before you sign the contract: pick the actual flooring, tile, fixtures and lighting and get the prices into the allowance. Then sign a selections schedule with dates so that nothing gets chosen in a showroom under pressure. The allowance guide and which decisions belong before construction are the two pages to read before that meeting.
What this looks like when it works
A couple came to us with 900,000 dollars all-in and a lot in Tiny Township they already owned. Servicing, design, permits, HST net of the rebate and a 15 percent contingency came to 190,000, leaving 710,000 to build. At a mid finish level that was a ceiling of about 2,200 square feet. They chose a bungalow with a walkout, ICF, radiant floors, nine-foot ceilings and a simple gable roof, and told the designer so. The sketch priced at 735,000; the designer took a foot off the garage, simplified the rear roof and moved one window, and the permit set priced at 704,000. They finished at 712,000, with contingency to spare, in a house that looks like it cost more. The trick was the order.
Related guides on this site
Sources and further reading
Questions people ask
How do I design a house to a budget?
Set the all-in number, subtract everything that is not construction, give the designer the construction budget with the cost levers already decided (shape, size, storeys, foundation, ceilings and glass, mechanical, finish level), and have a builder price the sketch before the permit set is drawn.
Why do house plans come in over budget?
Because they were drawn before anyone attached a number, and because the big cost decisions were left to the drawing instead of being made first. The redesign then costs more fees and months.
Will a builder price a sketch?
Most will, within a range, because the sketch that prices well is the one they get to build. Give them the finish level and the mechanical choices with it.
How much contingency should be in the budget before I design?
Ten to fifteen percent of construction on a serviced lot with complete drawings, more on rural or sloped lots. Take it out before you set the construction budget, not after.
Have a plan already?
Send it to ICFhome.ca and we will tell you what it costs to build and where the drawing is spending money you may not want to spend.
Reviewed and updated October 2026. Costs are Ontario ranges, not quotes; code references are to the Ontario Building Code in force at that date.
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