You need more room. The question is whether to buy it or build it. Most homeowners in Newmarket and across York Region start by comparing a listing price against a contractor's number, decide the addition is cheaper, and stop there. That comparison is wrong in both directions. Moving carries costs that never appear on a listing, and an addition carries costs that never appear in a per square foot estimate. This post puts both sets of numbers side by side, counts the months honestly, and says plainly when selling is the better answer.
The two numbers that actually decide it
The decision comes down to two totals, and almost nobody writes them down. The first is the all in cost of leaving: what you pay to sell your current house, what you pay to buy the next one, and what the difference in mortgage costs you every month for the rest of the term. The second is the all in cost of staying: construction, drawings, permits, temporary living arrangements, and the money you hold back for what the walls reveal once they are open.
Neither total is a single number you can look up, which is why most people substitute a proxy. The proxy for moving is the listing price of a bigger house. The proxy for building is a square foot rate somebody quoted at a barbecue. Both proxies understate the real figure by a wide margin, and they understate it unevenly, which is what makes the comparison misleading rather than merely rough. Transaction costs on a move are large, fixed and certain. Construction costs are smaller in the aggregate but far less certain, and the uncertainty sits entirely on your side.
The table below sets the two paths against the same criteria for a typical York Region scenario: a family in a $1.1 million house that needs about 600 more square feet. The dollar figures are market ranges drawn from what these transactions and projects generally run in 2026, not a price from this company. Your own numbers will move, sometimes a lot.
| What you are paying for | Sell and buy | Build an addition |
|---|---|---|
| Headline cost | $1.1M sale, $1.3M purchase | $210,000 to $330,000 of construction |
| Transaction taxes and fees | $22,475 land transfer tax, about $62,000 commission with HST, $4,000 legal | None |
| Drawings, permits, engineering | None | $10,000 to $30,000 |
| Reserve you should hold | Deposit and closing date risk | 10 to 15 percent of construction |
| Time from decision to done | 3 to 6 months | 9 to 15 months |
| Certainty of the final number | High, fixed at closing | Moderate, scope dependent |
What it costs to sell and buy in Ontario
Land transfer tax on a York Region purchase
Ontario charges land transfer tax on the buyer, on a sliding scale, at closing. On a $1.3 million purchase that works out to about $22,475. Toronto adds a second municipal land transfer tax of roughly the same size, which is one reason a move within York Region costs less than a move into the city.
Agent commission, legal fees and the moving bill
Commission is the biggest line. Four to five percent split between the listing and buying brokerages is common in the Greater Toronto Area, and at five percent on a $1.1 million sale that is $55,000 plus HST. Lawyers take $1,500 to $2,500 on each side. Add title insurance, a mortgage discharge penalty if you break a term early, staging and a mover, and another ten to fifteen thousand dollars is normal. None of it buys a single extra square foot.
The mortgage you would be signing at today's rate
This is the number people skip. If you hold a mortgage below what lenders are offering now, moving means retiring that rate and signing a new one on a larger balance. Trading a $600,000 balance at three percent for an $850,000 balance at four and a half can change your monthly payment by more than a renovation loan would. Run that difference over the full term before you decide.
What an addition costs to build in York Region
Market ranges per square foot for a rear or side addition
Across York Region a single storey rear addition generally runs $350 to $550 per square foot finished, and a two storey addition $300 to $500, because the foundation and roof are shared across more floor area. Those are market ranges, not a quote. What we include in an addition, and how we scope one, is set out on our Home Additions & Extensions page.
Permits, drawings and the fees the town charges
Newmarket requires a building permit for any addition, and the town charges the fee on the floor area you are adding, so it scales with the project. Budget for drawings before that: a designer or architect typically charges two to six percent of construction cost for a permit set. Zoning review, lot coverage and setback checks happen at the same counter, and a minor variance adds months if your addition does not fit the by-law.
Where an independent professional engineer is required
Some of this work genuinely needs a stamp. Removing a load bearing wall to open the house into the new space, carrying a new beam, or underpinning a foundation all require drawings sealed by an independent professional engineer. We arrange a licensed engineer to stamp the drawings. Electrical, gas and plumbing work is performed by licensed subcontractors under our project management. Budget $2,000 to $6,000 for structural engineering on a typical addition.
The contingency you should be holding
Hold ten to fifteen percent of the construction cost in reserve. Older Newmarket houses hide undersized footings, knob and tube, and grading that has to change once the new roof sheds water.
Months of disruption, honestly counted
A realistic schedule from first drawing to final inspection
Design and drawings take six to twelve weeks if you are decisive. Permit review in Newmarket runs roughly ten to fifteen working days once the submission is complete, longer if the town asks for revisions, and much longer if you need a minor variance, since committee of adjustment hearings are scheduled monthly. Construction on a 600 square foot rear addition is typically four to six months. Excavation and foundation are weather dependent, so a project that starts in November loses time that a project starting in April does not. Add the gap between signing and a crew actually being free. Nine to fifteen months from first sketch to final inspection is the honest range.
Living in the house while it is being built
Most families stay through the build. A rear addition is separated from the house by a temporary wall for much of the build, and the kitchen usually survives until tie in. What you lose is the back yard, quiet weekday mornings, and the use of one or two rooms for the duration. Expect dust past any barrier, trades arriving at seven, and a portable toilet in the driveway for months. If the addition includes a new kitchen, plan six to eight weeks of a temporary kitchen somewhere else in the house. Families with a newborn, a shift worker, or someone working from home on calls all day are the ones who end up renting, and a three month rental at Newmarket rates is a real line in the budget.
When moving is the better answer
Sometimes the house is simply the wrong house. If the lot cannot take the footprint, the answer is moving. Newmarket zoning sets lot coverage, side yard setbacks and a rear yard minimum, and on a small interior lot an addition big enough to matter will not fit inside them. A minor variance is possible, not guaranteed, and it costs months to find out.
Moving also wins when what you want is not space. A different school catchment, a shorter commute, a bungalow because stairs are becoming a problem, or a smaller house because the kids left are all things construction cannot deliver. If the finished value would land well above the top of your street, you are building equity you cannot get back out.
Reasons building usually wins
- You keep the neighbourhood, the school and the mortgage rate you already signed.
- No land transfer tax, no commission, no closing costs on either side of a sale.
- You get exactly the rooms you drew, rather than the closest compromise on the market.
Reasons it goes wrong
- Your money is locked in a site with nothing finished to walk away from.
- The schedule is not fully in your control, and a bad winter costs weeks.
- You live in the project, and that cost is paid in months, not dollars.
How to price both options before you commit to either
Get both numbers to the same level of detail before you choose. On the moving side, ask an agent for a realistic sale price on your house and the actual range for what you would buy, then add land transfer tax, five percent commission plus HST, legal fees on both transactions, and the mover. Take that total to your lender and ask what the new mortgage payment would be at today's posted rate.
On the building side, do not accept a per square foot number as a price. Pay a designer for a concept and a preliminary floor plan first, then take that drawing to two or three general contractors and ask for a scoped estimate with allowances named line by line. An estimate without allowances for flooring, cabinetry, windows and fixtures is not comparable to one that has them. Ask each contractor what they exclude, who holds the permit, and which trades are subcontracted.
Residential building construction costs across Canada's fifteen largest metropolitan areas rose 2.3 percent year over year in the second quarter of 2026.
Statistics Canada, 2026. Building construction price indexes, second quarter 2026
Then hold the two totals next to each other and add the contingency to the building side and the months to both. Construction pricing is not static while you deliberate, which is the last thing to factor in. A design that sits on a shelf for a year is usually a design that gets rebid higher.
