Basement Underpinning in Markham, ON
OCM Excavation & Construction underpins Markham basements from Unionville to Cornell to Cathedraltown and Berczy. If you bought a 1990s or 2000s Markham home with a 7-foot basement and want it lowered for a real lower level — a media room, a code-height in-law suite, a home gym with platform space — we dig under the existing footings in pin sections, pour new concrete piers, and rebuild the slab 18 to 36 inches lower. Call 416-317-3090 to book a Markham site visit.
Why Markham Homeowners Underpin
Most of the Markham housing stock we work on is post-1985 — Unionville, Markville, Cornell, Berczy, Cathedraltown, Box Grove. These houses were built to a tract spec with 7-foot basement ceilings, which was the norm then. It is not the norm now. Markham owners call us when they want a finished basement that feels like the rest of the house, when they want a multi-generational suite for parents moving in, or when they are converting to a code-legal rental to offset the cost of a Markham mortgage. The City of Markham now permits secondary suites in most residential zones, and basement underpinning is what makes that suite legal under the Ontario Building Code height minimums.
Markham Soil and What That Means
Markham sits on Halton Till — clay and silt with embedded stones — with shallow bedrock under parts of Unionville and Buttonville, and sandier deposits near the Rouge River corridor. Markham clay is dense and structurally strong, which is good for underpinning footings, but it holds water and heaves with freeze cycles. If we hit shallow bedrock during the dig we shift technique to mechanical breaking or, where possible, redesign the depth so we stop above competent rock. Either way, the soil profile dictates pier widths, shoring and dewatering. We assess soil during the site visit and price accordingly — no surprises mid-job.
Markham Permits
Underpinning in Markham requires a building permit from the City of Markham Building Standards Department at the Markham Civic Centre on Town Centre Boulevard. You need stamped structural drawings from an Ontario-licensed Professional Engineer, a site plan, and where you are creating a secondary unit the Second Suite registration is filed at the same time. Permit fees vary by floor area and project scope — the City of Markham publishes the current rate schedule on its website. We pull the permit, coordinate engineering, and book inspections at the required stages.
Typical Markham Underpinning Cost
A standard Markham detached with a 1,000 to 1,400 square foot basement footprint runs $50,000 to $90,000 for full underpinning, depending on depth, soil conditions, exterior waterproofing scope, slab replacement, weeping tile, sump and any rough plumbing for a suite. Cornell townhomes with smaller footprints come in lower. Cathedraltown or Berczy estate homes with 1,800+ square foot basements run higher. The number on a phone call is a guess. The number after a site walk is a quote — call 416-317-3090 to book it.
Equipment on Markham Sites
Most Markham lots support machine access, so we run a Yanmar SV40 mini-excavator into the basement through a cut access. That cuts the structural phase by 1 to 2 weeks compared to full hand-dig. On tighter Cornell or Old Markham infill lots we revert to hand-dig with barrows. Either way the underpinning sequence — pin sections, shore, dig, form, pour, cure, advance — does not change.
Related Markham Services
Most Markham underpinning jobs pair with exterior waterproofing and weeping tile replacement. See our Markham foundation waterproofing page and our Markham excavation contractor page. We also serve neighbours — see underpinning in Richmond Hill and underpinning in Scarborough. Full coverage at our service areas.
Frequently Asked Questions
How long does Markham underpinning take?
Structural underpinning runs 5 to 8 weeks on a standard Markham detached. Add 2 to 4 weeks for exterior waterproofing, a new slab, weeping tile and rough plumbing for a suite. Cathedraltown and Berczy estate homes can run 10 to 12 weeks. Permit and engineering lead time adds another 4 to 8 weeks before we break ground.
Does Markham allow basement apartments?
Yes. The City of Markham permits secondary suites in most residential zones. You file the Second Suite registration with the building permit, the basement must hit Ontario Building Code ceiling height and egress, you need proper fire separation and HVAC, and you book a final inspection. Underpinning is usually how Markham basements get to the required height.
What happens if you hit bedrock under my Markham basement?
Shallow bedrock shows up in pockets of Unionville and Buttonville. If we hit competent rock above the target depth, we either shift to mechanical breaking — which adds cost and time — or, with the engineer’s approval, redesign the depth so we stop above the rock and accept a slightly lower headroom gain. We test conditions during the dig and decide with you before continuing.
Do I need to move out during a Markham underpinning?
Most Markham owners stay in the house during underpinning. The basement is sealed off, dust control is run, and the loudest work is scheduled mid-day. If you have a newborn, work from home with calls all day, or have pets that cannot handle vibration, plan a partial relocation. We will tell you straight up what to expect.
Is underpinning cheaper than building an addition?
Yes, almost always — per square foot of usable space. A Markham rear addition runs $400 to $700 per square foot finished. Underpinning to make existing basement square footage usable runs roughly $200 to $300 per square foot of basement, all-in with waterproofing and slab. You also keep your full back yard.
Book Your Markham Underpinning Quote
Call 416-317-3090 or use the free quote form. We will walk your Markham basement and follow up with a written number.
Phone 416-317-3090.Related Services in Markham
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in Markham? Let’s talk.