How to Waterproof a Basement From the Inside (And When It's Not Enough)

Interior basement waterproofing is the most-misunderstood category of work we do. Here's the honest version.

What we actually install

A perimeter drainage channel cut into the basement floor along the wall-floor joint. Water that enters at this joint drops into the channel, runs by gravity to a sump pit, and is pumped out.

Above that, an interior drainage membrane (a plastic sheet with dimples) often runs up the wall to direct any wall seepage down into the channel.

When interior is the right answer

Floor-wall joint seepage. Hydrostatic pressure pushing water up from below. Inaccessible exterior walls. Minor manageable problems on a budget.

When interior is NOT enough

Active wall cracks. Severe chronic seepage. Bowing or structurally compromised walls. Mold caused by ongoing wall moisture. In those cases you need exterior — interior alone will manage the symptoms but not solve the problem.

The bottom line

Interior waterproofing is a real, valid solution for the right problem. But if a contractor offers ONLY interior solutions for every job, get a second opinion.

Get a free inspection in Markham

If you've noticed dampness, cracks, or musty smells in your basement, don't wait. We offer free on-site inspections across Markham, Unionville, Cornell, Berczy Village, Cathedraltown, Markville and Thornhill — and our work is backed by a written workmanship warranty.