Waterproofing Service in Markham

Markham's clay-heavy soil and freeze-thaw winters put steady pressure on basement walls and foundations, which is why waterproofing comes up constantly in older neighborhoods like Thornhill and Unionville as well as newer builds near Cornell. The 6 companies listed in this category handle everything from interior weeping tile repair to full exterior excavation and membrane installation.

What waterproofing actually involves

Most jobs fall into one of two categories. Interior waterproofing means installing a drainage system (weeping tile) along the interior perimeter of the basement floor, connected to a sump pump, to intercept water before it seeps through the walls. Exterior waterproofing is more invasive: crews excavate down to the footing, apply a membrane or coating to the foundation wall, install or replace the drainage tile outside, and backfill. Exterior work costs more and takes longer, but it stops water from reaching the concrete in the first place rather than just managing it once it's inside.

What to look for before you sign a contract

Ask whether the quote includes permits, backfill compaction, and downspout or grading corrections, since water problems are often made worse by poor drainage around the house, not just a cracked foundation. Get a written warranty term and ask what voids it. Check how the contractor diagnoses the source of leaks before recommending a fix. A crew that wants to dig immediately without inspecting grading, gutters, and window wells is skipping a step that matters.

How we score contractors

Our rankings weigh warranty terms, diagnostic process, licensing, and verified customer feedback rather than just price. See the full breakdown of criteria on our methodology page, and compare all renovation trades in the area on our ranked guide to Markham renovation contractors.