Design-and-build basement finishing for Markham homes—family rooms, suites and baths, delivered fixed-price, insured and structure-first.
GMC Construction finishes and remodels basements across Markham for family living, work, recreation, guests and approved secondary suites. We coordinate planning, permits, framing, insulation, plumbing, electrical work, waterproofing, entrances and finishes through one accountable process.
Markham’s housing stock creates several different basement opportunities. Newer family homes in Cornell, Wismer, Berczy Village and Cathedraltown often have substantial unfinished lower levels that can become a family room, office, gym, guest area or an approved secondary suite. Larger homes around Angus Glen may call for custom entertainment or multi-purpose spaces. In Unionville, Markham Village, Milliken Mills and older parts of Thornhill, the basement may need more investigation of ceiling height, moisture, foundation openings and dated services before finishing begins.
GMC starts with the conditions behind the future walls. We review water entry, foundation and slab moisture, ceiling height, windows and exits, insulation, HVAC, plumbing, electrical capacity, beams, columns and stairs before finalizing rooms. That early assessment helps distinguish a straightforward finish from a project involving a new bathroom, second unit, entrance, underpinning or other structural work.
Structure-first planning
GMC’s owner is a civil engineer with a master’s degree in structural engineering. The company has completed 500+ projects, holds a 5.0-star rating with 85+ Google reviews, and is insured with WSIB coverage.
We serve Unionville, Cornell, Wismer, Berczy Village, Cathedraltown, Angus Glen, Markham Village, Milliken Mills, the Markham side of Thornhill and surrounding neighbourhoods. For broader service information, visit our GTA basement renovation hub or Markham renovation services page.
These 2026 planning ranges are before HST and must be confirmed against the measured area, existing conditions, selections and permit scope.
| Basement tier | Planning rate | Typical total | Typical scope |
|---|---|---|---|
| Basic recreation room | $45–$65 per sq. ft. | $25,000–$45,000 | Framing, insulation, drywall, basic electrical and lighting, flooring, trim and paint for a straightforward family or recreation space. |
| Mid-range with bathroom | $65–$90 per sq. ft. | $45,000–$85,000 | Broader finishing plus a bathroom, upgraded lighting, storage and coordinated plumbing, ventilation and finishes. |
| High-end or secondary suite | $90–$150+ per sq. ft. | $85,000–$150,000+ | Custom rooms or an approved suite with kitchen area, bathroom, fire and acoustic assemblies, egress and permit-driven work. |
Cost is affected by finished area, ceiling height, demolition, moisture correction, foundation and slab conditions, bathroom or kitchen plumbing, electrical and HVAC upgrades, insulation, fire separation, egress windows, entrances, underpinning, cabinetry and finish level. Design, permit and inspection requirements depend on the intended use.
Read our basement renovation cost guide for more planning detail. A fixed-price quote still requires a property-specific assessment.
Complete finishing can transform an open or dated basement into a family room, office, gym, playroom, guest area or a combination of uses. GMC coordinates layout, framing, insulation, HVAC, electrical work, drywall, ceilings, flooring, trim, doors and paint as one project. Mechanical rooms, support posts, stairs and access panels are incorporated deliberately. The plan also preserves service clearances and routes for equipment, valves and cleanouts.
A secondary suite is a self-contained dwelling unit, not simply a finished basement with extra cabinets. Markham’s current guide identifies eligible configurations in detached houses, semi-detached houses and row townhouses, subject to zoning, the Ontario Building Code, permits and the City’s registration process. The design must address kitchen and bathroom facilities, a protected path to exit, fire and acoustic separation, alarms, ventilation, plumbing and other property-specific requirements. Markham’s guide illustrates both separate and code-compliant shared entrance arrangements, so the approved exit design—not a generic assumption—controls the project.
A basement bathroom requires coordinated drainage, venting, water supply, ventilation, electrical work, waterproofing and ceiling-height planning. An existing rough-in is useful only after its location, elevation and condition are confirmed. GMC can build a powder room, full bathroom or ensuite within the larger basement plan. Markham requires permits for bathroom rough-ins, new plumbing and the construction of separate basement rooms.
A wet bar can support family entertaining without creating a separate dwelling. A kitchenette may include cabinets, a countertop, sink and specified appliances, with plumbing, electrical load and ventilation coordinated to the intended use. If the facilities and layout create an independent residential unit, second-unit rules may apply regardless of the label. We clarify the use before drawings and pricing are finalized.
A side entrance or excavated walk-up can improve access to a family basement or form part of an approved suite design. Work may include excavation, a foundation opening, retaining walls, stairs, drainage, waterproofing, grading, guards, handrails and site restoration. Markham identifies installation of a basement entrance as permit work. The proposed entrance must be reviewed with the property’s zoning, grading, services and suite design. Visit our separate basement entrance page for more detail.
Underpinning can lower the slab by extending the foundation in carefully sequenced sections. Benching may create a lower floor while retaining an interior stepped or sloped mass around the foundation. Each method affects usable floor area, structure, drainage and construction access differently. This is property-specific structural work requiring design, permits and controlled sequencing. Neighbouring conditions and soil must be considered before a method is recommended.
Water staining, efflorescence, damp foundation walls or floor seepage should be investigated before insulation and drywall conceal them. The correct response may involve exterior waterproofing, crack repair, drainage improvements, interior water management or another solution tied to the source. A coating is not a universal answer. GMC separates active water entry from normal vapour and condensation control and defines the applicable work before finishing starts.
Bedrooms and secondary suites may need windows that satisfy applicable light, ventilation and emergency-escape requirements. Opening size, window well, drainage, grade, property lines and foundation construction must be reviewed together. Enlarging a foundation opening can require structural design and a permit. GMC coordinates the window, well, drainage, waterproofing and structural details within the approved scope.
Basement wall assemblies must suit the foundation, moisture conditions and energy requirements. Framing, insulation, air and vapour control, fire blocking and drywall are coordinated instead of copied directly from an above-grade wall. Bulkheads and access panels are planned around ducts, drains, valves and wiring. Required fire separations use specified assemblies and protected penetrations.
Flooring is selected after the slab is reviewed for moisture, flatness, temperature and transitions. Options may include luxury vinyl, laminate, engineered products, tile or another basement-compatible system. Active water or significant slab moisture must be addressed first. Underlayment and finish flooring cannot replace drainage or leak repair.
Recessed lighting can brighten a basement while preserving headroom, but locations must coordinate with joists, ducts, fire separations and room use. Task, accent and stair lighting may also be included. Circuits, receptacles, smoke and carbon-monoxide alarms and service capacity are planned with the full renovation. Electrical work follows the applicable ESA process.
The City of Markham identifies finished basements, construction of separate basement rooms, bathroom rough-ins, new plumbing, basement entrances, structural wall changes and accessory apartments as permit work. Applications are submitted through Markham’s ePLAN system and must include the drawings and supporting documents required for the scope.
For a secondary suite, the City’s current homeowner guide covers zoning eligibility, Building Code design, permit submission and registration with Markham Fire and Emergency Services. Permit drawings may need to show the suite layout, entrance and exit windows, fire-separation construction, structural framing, plumbing and HVAC. A protected path to exit is essential; a private exterior entrance is one option, but Markham’s guide also illustrates an approved shared-entrance arrangement.
Underpinning, benching, foundation openings and some wall changes are structural work. The owner’s structural-engineering background informs early planning, while an independent third-party engineer provides stamped structural drawings where required. Excavation and structural changes follow the approved design and inspection sequence.
Moisture and waterproofing are assessed before finishes cover the foundation. A building permit does not diagnose every water source, so leaks, drainage and foundation conditions are addressed separately in the construction plan.
We review the intended use, ceiling height, foundation, moisture indicators, mechanical systems, plumbing, electrical service, windows, stairs and access. Once the scope and visible assumptions are defined, GMC provides a written fixed-price quote with inclusions, allowances and exclusions.
The room plan, bathroom or kitchen facilities, entrances, egress, assemblies, finishes and service routes are coordinated. Required drawings, third-party engineering, ePLAN submissions and key selections are completed before affected construction starts.
GMC manages protection, demolition, water or structural work, framing, insulation, plumbing, electrical work, HVAC, inspections, drywall, flooring, millwork and finishing in the correct sequence. One point of contact coordinates the trades and decisions.
We review the completed basement with the homeowner, document remaining items and provide applicable project information. GMC also supplies a written workmanship warranty.
Foundation openings, posts, wall changes and ceiling-height work are reviewed early. Work requiring professional design is coordinated with an independent third-party engineer.
Visible staining, active leaks and drainage concerns are reviewed before walls and flooring cover the basement. A finish package is not represented as waterproofing repair.
Finishing, plumbing, entrances and second units have specific permit and documentation requirements. GMC coordinates the applicable drawings, ePLAN submission and inspections for the defined scope.
Basement work may involve structural, waterproofing, framing, plumbing, electrical, HVAC, drywall and finish trades. GMC manages the related work through one project process.
GMC is insured and has WSIB coverage. The company has completed 500+ projects, maintains a 5.0-star rating with 85+ Google reviews, provides fixed-price quotes and issues a written workmanship warranty.
Planning a basement in Unionville, Cornell, Wismer, Berczy Village, Cathedraltown, Angus Glen, Markham Village, Milliken Mills or Thornhill? Use the form to tell us whether the goal is family space, a bathroom, an entrance or an approved secondary suite.
