Basement Waterproofing Cost in Seattle [2025 Data]

With the average basement waterproofing cost in Seattle near $4,257, homeowners in the Emerald City are paying above the national average for this project. Overall, Seattle homeowners can expect to pay between $2,345 and $6,245 for basement waterproofing. Factors such as basement size and the scope of the chosen waterproofing technique influence costs. Continue reading to discover how to budget for Seattle basement waterproofing costs.

Basement Waterproofing Cost Factors 

With Seattle having more than 150 rainy days on average each year, waterproofing is high on the priority list for homeowners. With basements being uncommon in Seattle due to the city's complex geological characteristics and high water table, many common basement waterproofing techniques that are available for homes in the city with basements can also be used for concrete slab foundations. Contractors who offer basement waterproofing in Seattle will look at factors like a property's orientation and signs of basement water damage that already exist to create a plan for blocking water intrusion. 

Basement Size

The cost to waterproof a basement falls between $3 and $10 per square foot on average, although where in this range your pricing falls depends largely on the type of waterproofing method you choose. In any case, large spaces require more time, labor, and material to waterproof than small spaces. Therefore, the larger your basement, the more you can expect to pay for waterproofing for any given method.

Below is a breakdown of how much you might spend for a range of basement sizes.

Interior vs. Exterior Waterproofing

Depending on where your basement water issues are stemming from and what solutions your expert recommends, you may need either interior or exterior waterproofing services. Some homes require both. Interior basement waterproofing is often more affordable because it doesn’t involve excavation and backfilling. Something like installing damp-proofing around the exterior of your foundation would require a lot of digging, which drastically increases labor costs.

You’ll spend an average of $3,000 on interior waterproofing services, while extensive exterior services will cost an average of $7,000.

Waterproofing Method

As mentioned above, professionals can waterproof your basement from the exterior or the interior. Exterior methods are more effective because they’re preventative, but they’re also more expensive because they tend to require excavation, which is time-consuming. The table below includes a list of basement waterproofing methods along with cost ranges for each.

Basement Waterproofing Pro Costs

Basement waterproofing pros in Seattle base their quotes on project scope. This means that pricing largely depends on the type of waterproofing method you choose. That choice will ultimately determine the cost for materials, permits, and labor needed to get the job done.

Permits

In general, any basement or foundation waterproofing project in Seattle that involves excavation, drainage, or structural changes to your home or yard will require a permit. When you hire a local waterproofing pro, they will submit all permit applications and payments to the Seattle Department of Construction & Inspections (SDCI). On average, a project that combines drainage/plumbing and excavation could incur between $500 and $1,200 in city permit fees.

Local Labor

Basement waterproofing professionals in Seattle generally charge between $180 and $210 hourly. When setting rates for basement waterproofing, contractors might bill by square foot after factoring in the hours, materials, and number of laborers needed.

Taxes

With repair work and construction labor being subject to Seattle sales tax in many cases, Seattle homeowners will need to budget for the extra taxes added to both labor costs and material costs when getting their basements waterproofed. A 6.50% Washington sales tax and 3.85% Seattle sales tax bring the total rate to 10.35%.

Insurance

With King County requiring all contractors to carry general liability insurance, waterproofing contractors can pay up to $190 to $200 per month. For contractors with employees, the cost for the required workers' compensation insurance can total another $100 to $200 monthly.

Licensing Certification

Washington State requires all construction contractors to register with the Department of Labor & Industries (L&I). While the initial fee is $141.10, contractors must also budget for renewal fees totaling $117 to $124.

Does Basement Waterproofing Increase Home Value?

With most estimates placing the investment (ROI) for waterproofing a basement in Seattle at up to 80%, it's clear that waterproofing is an important investment. By preventing water intrusion, homeowners can protect their homes from foundation issues and mold that could lead to expensive water damage restoration costs. Seattle's wet climate means that buyers often prioritize basement and foundation inspections before purchasing homes.

How Angi Gets Its Cost Data

Home is the most important place on earth, which is why Angi has helped more than 150 million homeowners transform their houses into homes they adore. To help homeowners with their next project, Angi provides readers with the most accurate cost data and upholds strict editorial standards. We survey real Angi customers about their project costs to develop the pricing data you see, so you can make the best decisions for you and your home. We pair this data with research from reputable sources, including the U.S. Bureau of Labor Statistics, academic journals, market studies, and interviews with industry experts—all to ensure our prices reflect real-world projects. 

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