Waterproofing in Washington

Yes — reputable structural waterproofing comes with an insurance-backed guarantee so the cover survives if the contractor ceases trading. Ask whether the guarantee is company-backed or independently insured, because a company-only warranty is worth little if they close.

Wet areas need a waterproof membrane behind tiles on floors and walls, correctly detailed at junctions and drains. In many countries this is regulated work with a standard to meet — a failed shower membrane is one of the most common and costly building defects.

Damp proofing resists moisture and rising damp (like a damp-proof course in a wall); waterproofing resists liquid water under pressure, as in a basement below the water table. Below-ground and wet-area work needs true waterproofing, not just a damp treatment.

It depends on the method and area. Internal sealants and damp-proofing for a small area are the cheapest option; cavity-drain membranes and tanking cost more; a full basement or below-ground waterproofing system is the most expensive, running into five figures. The cause of the water dictates the right system.

Small sealant jobs on a minor damp patch are DIY-able, but below-ground waterproofing against groundwater pressure is specialist work — get it wrong and you trap water or flood the space. Full basement systems should be designed and installed by a qualified specialist.

Interior sealant and drainage jobs commonly run $3,000-$7,000, while exterior excavation-and-membrane systems run $5,000-$15,000 or more. Small damp-proofing tasks start under $1,500.