Full Basement Renovation in Unionville: What the Houses Do

A client calls from Carlton Road with a 1974 side-split and a basement ceiling that measures 6 feet 11 inches at the beam. Another calls from Village Parkway with a 1996 two-storey and 8 feet 4 inches of headroom already poured. Both want finished space, both are in Unionville, and the difference in what we build for each of them is $48,000 on a 1,200 square foot level. The house decides half the budget before you choose a single finish.

Unionville sits in Markham's L3R postal area and runs roughly from Kennedy Road west to the Rouge River, Sixteenth Avenue south to Highway 7. The neighbourhood splits cleanly by decade: 1970s splits and bungalows on the older streets around Carlton, Kennedy and the heritage Main Street core, then 1990s and early 2000s two-storeys spreading north and east toward Village Parkway, Rodick Road and the newer cul-de-sacs off Bur Oak. The foundation work, the permit triggers and the cost of a full basement renovation in Unionville depend almost entirely on which era your house comes from.

What Unionville's housing stock looks like street by street

The streets around Main Street Unionville, Carlton Road, Kennedy Road south of Sixteenth, and the blocks between Highway 7 and Carlton hold the oldest stock: 1970s side-splits, back-splits and solid-brick bungalows on 50 to 60 foot lots, many with rubble-and-poured foundations, ceiling heights of 6 feet 8 inches to 7 feet 2 inches in the original pour, and fieldstone or concrete-block perimeter walls that were never meant to become living space. These are the houses where underpinning or a bench footing becomes the first line item.

North and east of Sixteenth Avenue, the subdivisions built from the late 1980s through the early 2000s, Village Parkway, Rodick, the streets off Bur Oak and Carlton east of Kennedy, are mostly two-storey colonials and Tudor-revival houses on similar frontages but with poured-concrete foundations, pre-drywall ceiling heights of 8 feet to 8 feet 6 inches, and footprints of 1,800 to 2,400 square feet. These basements arrive ready for finishing without structural intervention, which is why a basement renovation in Markham in this part of Unionville costs 20 to 35 percent less than one three streets south.

A few heritage houses remain around the Main Street conservation district and Fred Varley Drive: 19th-century fieldstone cottages and early-20th-century frame houses with crawl spaces or low rubble cellars that were dug by hand. Finishing those requires engineering, often underpinning, and heritage review if the work touches the exterior or the structure. We have done two; both cost more than building new space above grade would have.

Why 1970s splits on Carlton and Kennedy need more structural work

Side-splits and back-splits from the 1970s were built with a lower level half below grade and a ceiling height that met the Building Code's minimum for unfinished basements but falls short of what is comfortable, or legal, for habitable rooms today. The Ontario Building Code allows existing basements to be finished at 1.95 metres, about 6 feet 5 inches, but that is a minimum for code compliance, not for a room anyone wants to spend time in. Most builders and homeowners target 7 feet clear after flooring and ceiling, which means the original pour needs at least 7 feet 3 inches before you start.

When the existing slab-to-joist dimension is 6 feet 10 inches, you have two options: lower the floor or raise the joists. Raising the joists means jacking the entire house, which we do not recommend on a split-level where the floor planes are already offset. Lowering the floor means underpinning, which extends the footings downward in alternating one-metre sections, each poured and cured before the next, or installing a bench footing, an interior concrete ledge that costs roughly 45 to 60 centimetres of usable width around the perimeter. Underpinning on a typical Unionville split runs $32,000 to $54,000 depending on depth and soil; a bench footing runs $18,000 to $28,000 but leaves you with a narrower room.

The splits also sit on Markham's glacial till and clay, dense soil that drains slowly and loads foundation walls after heavy rain. We see more foundation movement and hairline cracks in the 1970s pours than in the 1990s work, which means more remediation, more waterproofing from outside if the crack is active, and more engineering sign-off before we close walls. None of this shows in the original budget until we open the space and measure.

What ceiling height does to your budget in older Unionville

A 1,200 square foot basement in a 1997 Unionville two-storey with 8 feet 4 inches of existing height costs $84,000 to $132,000 finished to our standard: new partitions, full bathroom, wet bar, luxury vinyl or engineered floors, pot lights, trim and paint. The same program in a 1974 Carlton Road split with 6 feet 11 inches of existing height costs $118,000 to $172,000, because we underpin first, then build. The gap is 29 to 30 percent, and it comes entirely from the structure the original builder left you.

Underpinning adds 8 to 12 weeks to the schedule and moves the building permit from a routine basement-finishing application to a foundation-alteration file that requires engineering drawings, a geotechnical opinion on bearing capacity, and sometimes a third-party review if the house is semi-detached or part of a row. Markham Building Standards processes complete house applications in roughly ten business days, but incomplete applications stop the clock, and foundation work is where files most often come back for more detail.

The arithmetic: underpinning at $38,000, new slab and vapour barrier at $8,200, then the standard finishing scope. On a 1990s foundation we skip the first two line items and start with framing. The homeowner on Carlton sees a higher number, but they also get 7 feet 6 inches of clear height and a basement that feels like a lower level, not a bunker. We would rather underpin than finish a 6-foot-10 space and have the client resent it for twenty years.

Permit triggers for basements in Unionville Markham

Finishing a Unionville basement with new partitions, plumbing, electrical or any structural change requires a building permit from City of Markham Building Standards. Cosmetic work, paint, flooring and trim replacement in already-finished space, typically does not. The line is whether you are altering the building system.

Adding a bathroom triggers a plumbing permit and inspections at rough-in and final. A wet bar with a sink does the same. If you add a bedroom, the Building Code requires an egress window with an unobstructed open area of at least 0.35 square metres and no dimension less than 380 millimetres; window wells need clearance in front of the sash, and the details vary by configuration. Most 1990s Unionville basements have windows sized for egress already; most 1970s splits do not, which means cutting the foundation and installing a code-compliant well.

A legal second suite, a separate dwelling unit with its own kitchen, requires a building permit, must meet the Building Code's fire separation, egress and ceiling-height standards, and must be registered with the City of Markham under the second-unit program. The ceiling-height minimum for existing basements is 1.95 metres; many 1990s Unionville foundations clear it easily, most 1970s ones do not without underpinning. Fire separation is typically a 30-minute assembly, interconnected smoke alarms and carbon monoxide alarms are mandatory, and the suite needs a separate entrance or a door opening directly to grade.

Inspections follow the build in stages: framing, plumbing rough-in, insulation and vapour barrier, HVAC if you extend ductwork, and final occupancy. Covering work before an inspection is the classic cause of a stop-work order. We schedule inspections as the trades finish so nothing waits and nothing gets covered early.

What a typical Unionville basement renovation costs in 2026

A full finishing scope on a 1,400 square foot Unionville basement, 1990s foundation with existing 8-foot-plus ceiling height, runs $98,000 to $154,000. That includes new framing and drywall, one full bathroom, a wet bar with undercounter fridge and sink, luxury vinyl plank or engineered hardwood, pot lights on dimmers, trim, two coats of paint, and a small mechanical allowance for extending HVAC and adding a dehumidifier. No theatre, no wine room, no second kitchen.

The same scope on a 1970s split requiring underpinning runs $142,000 to $208,000, with the gap covering foundation work, engineering, the extended permit process and the new slab. If the client wants a legal second suite, add $18,000 to $32,000 for the separate entrance, the fire-rated separation, the code-compliant egress window and the registration process. A basement bathroom alone, depending on finishes and whether we rough new lines or tap existing stubs, runs $22,000 to $42,000; see what a basement bathroom costs for the breakdown.

Luxury programs, theatres with acoustic isolation, glass-walled wine cellars, full gyms, price as defined packages. A Dolby-calibrated theatre in an Angus Glen basement, similar work to our Angus Glen spa suite, runs $68,000 to $95,000 depending on seating and equipment. A conditioned wine display with glass and lighting runs $24,000 to $38,000. These numbers assume the structure is ready; if we underpin first, add the foundation cost to every line.

Design moves that work with Unionville lot sizes

Unionville lots run 50 to 60 feet wide and 110 to 130 feet deep, which gives you a basement footprint of roughly 1,600 to 2,200 square feet under a typical two-storey and 1,200 to 1,600 under a split. That is enough space to separate a theatre or games room from a guest suite, to run a full bar and lounge without the furniture touching, and to add a gym or a hobby room that does not borrow space from storage.

We push mechanical and storage to one end, usually the side farthest from the garden entrance or walkout if the lot has one, then build the program as a sequence of rooms rather than one open space. Unionville clients use basements for multi-generational living, for entertaining extended family, for mahjong and card nights, and for the kind of hosting that needs a wet bar, a tea station and a powder room that guests do not have to hunt for. Open-concept basements do not serve that life as well as defined rooms do.

On the 1990s houses with higher ceilings, we often build a media wall with backlit onyx or stone, a concealed projector, and acoustic panels that look like millwork. On the 1970s splits where we have underpinned to 7 feet 6 inches, we keep the ceiling simple, use recessed lighting and avoid dropped soffits that would claw back the height we just paid for. The lot size is not the constraint in Unionville; the ceiling height is.

When a bathroom or second suite makes sense here

A bathroom makes sense when the basement program includes a guest suite, a games room that will be used for hours at a time, or a teenager's den that effectively becomes their floor. We see the most regret from clients who finished 1,800 square feet and skipped the bathroom because it seemed expensive at the time; two years later they are opening walls to rough one in, and the cost is now double.

A legal second suite makes sense when the household is multi-generational, when aging parents or adult children will live in the house long-term, or when the homeowner wants the option to rent the space and offset the mortgage. Unionville's 1990s stock, the houses on Village Parkway, Rodick and the streets north of Sixteenth, often has the ceiling height to make an outstanding suite without underpinning. The 1970s splits can too, but only after we lower the floor, and that decision turns on whether the household will use the space for a decade or more. If the answer is three years, underpin for a suite does not pay back.

We would add the bathroom. We would add the suite if the family structure calls for it and the house is 1990s-or-newer. We would not underpin a 1974 split for a suite the client thinks they might rent someday. The trade-off we accept: a smaller basement with higher ceilings and no suite beats a tall basement with a suite no one wants to live in because the ceiling is 6 feet 7 inches.