Basement Waterproofing in Chilliwack, BC

Interior vs Exterior Waterproofing: Which One Your Basement Needs

Basement waterproofing splits into two different approaches: interior systems that manage water after it reaches the foundation wall, and exterior systems that stop water from reaching the wall at all. The right choice depends on what's causing the water, not only where you notice it.

Interior waterproofing captures water at the base of the wall or under the slab and redirects it to a sump pump before it can spread across the floor. It's less invasive: no excavation, no landscaping disruption, and work is typically done in a day or two from inside the basement.

Exterior waterproofing involves excavating along the foundation down to the footing, applying a waterproof membrane directly to the wall, and installing a drainage layer that carries water away from the foundation rather than through it. It's more disruptive and more expensive, but it addresses the source rather than the symptom, and it's the only real option when the wall itself needs fresh damp-proofing or when grading around the house is part of the problem.

How Exterior Waterproofing Works

Exterior waterproofing starts with excavation around the foundation, down to the footing. Once the wall is exposed, we repair any visible cracks or damage, then apply a waterproofing membrane. Two systems dominate the market: rubberized asphalt or elastomeric coatings applied as a liquid membrane, and dimpled HDPE sheet membrane (Delta-MS is the common brand), fastened mechanically over the wall.

The dimpled membrane approach has an advantage worth knowing: the raised dimples create an air gap between the membrane and the wall, acting as a capillary break so water can't wick through by surface tension even if the coating below has a flaw. Liquid membranes need 24 to 48 hours of cure time before backfilling; dimpled sheet membrane can be backfilled as soon as it's mechanically fastened, which shortens the job.

A drainage board or new footing drain typically goes in alongside the membrane, carrying water down to grade and away from the foundation rather than letting it pool against the wall. The excavation is backfilled last, usually with clean granular material rather than the original soil, to keep water moving away instead of holding it against the concrete.

Interior Systems and How They Tie Into Your Basement

Interior waterproofing usually centers on a drain tile system installed along the inside perimeter of the basement floor, just below the slab, which channels water to a sump pump for discharge outside. We cover this system in more depth on our interior drain system page, since it's often sold and installed as its own project. Interior waterproofing can also include wall membranes, vapour barriers on exposed concrete, and crack injection for any active leaks found during inspection, layered together rather than relying on one fix.

The honest tradeoff: interior systems manage water that's already inside the wall assembly. They don't stop water from reaching the concrete, so the wall stays wet on the outside even after the inside stays dry. For most Chilliwack basements with moderate seepage, that's a fine tradeoff for the lower cost and faster timeline. For homes with a high water table or repeated hydrostatic pressure, exterior work is usually the more durable long-term fix.

Cost and Timeline

Interior waterproofing typically runs $70 to $150 per linear foot, with most homes landing in the $3,000 to $10,000 range depending on basement size and how much of the perimeter needs coverage. It's usually completed in one to two days.

Exterior waterproofing runs considerably higher, generally $150 to $250+ per linear foot, because of the excavation, membrane material, and backfill involved. A full perimeter job often lands in the $10,000 to $35,000+ range for an average home, and takes several days to a week depending on access, landscaping, and how much of the foundation needs to be exposed.

Access is the biggest cost driver on exterior work specifically: a foundation with a deck, patio, or mature landscaping built up against it costs more to excavate than one with clear yard space. We walk the full perimeter during the free inspection and give you a written number broken out by section, so you know what's driving the cost before agreeing to anything.