Basement Waterproofing Cost in Maine and New Hampshire: 2026 Guide

National cost guides put basement waterproofing at $3,000 to $10,000 and leave it there. That range doesn’t account for what granite ledge three feet below grade does to an excavation budget in Kennebec County, or what a high water table in the Merrimack Valley adds to a drainage system in southern New Hampshire. Maine and NH have regional conditions that push projects above national averages far more often than below them.

This guide covers what waterproofing actually costs here, broken down by method and linear footage, with the regional factors that move the number up or down.

What basement waterproofing costs in Maine and New Hampshire

Statewide averages from Angi and HomeAdvisor put Maine at $6,500 and New Hampshire at $6,800 for a typical residential project. Those numbers are accurate but they average out a wide spread. A minor seepage issue in a poured concrete wall in a 1990s ranch is a very different job from a block foundation in a 1940s farmhouse sitting in heavy clay soil with no original footing drain.

Here’s what the range actually looks like by method:

• Interior perimeter drain with sump pump: $3,500 to $6,500
• Exterior excavation and membrane waterproofing: $8,000 to $14,000
• Crack injection only, for minor localized seepage: $500 to $1,500 per crack
• Full system in an older home with a compromised foundation: $15,000 to $30,000+

The top of that last range reflects real projects in Maine, not outliers. A 1,200 square foot basement in an older farmhouse with block walls, no original drainage, clay-heavy soil, and limited site access can run into five figures before you factor in the sump pump.

Source: Angi and HomeAdvisor regional data, cross-referenced with Maine and NH contractor pricing as of 2026.

Cost per linear foot: the number to ask for

Most contractors price interior waterproofing by linear foot of perimeter treated. Asking for a per-linear-foot number lets you compare bids on the same unit rather than trying to reconcile lump sums that may not include identical scope.

In Maine and New Hampshire, current pricing runs:

• Interior French drain (perimeter channel under or alongside the slab): $58 to $85 per linear foot, installed
• Exterior foundation waterproofing (membrane applied to the outside wall face): $99 to $140 per linear foot, before excavation complications
• Sump pump installation, required with any interior drain system: $800 to $2,500 depending on horsepower, brand, and basin depth

For a 1,200 square foot home with roughly 140 linear feet of perimeter, an interior drain system with a pump runs approximately $9,000 to $14,000 in this region. That’s above the national midpoint, but it reflects New England labor rates and the deeper installation required to stay below frost line.

What actually drives the price in Maine and New Hampshire

Two regional factors push local waterproofing costs above national averages more than anything else.

Granite ledge. Large portions of Maine, particularly inland and coastal areas away from river valleys, have bedrock within a few feet of the surface. Exterior excavation that’s routine in Pennsylvania or Ohio becomes a different conversation when the contractor hits ledge at three feet. Drilling and blasting adds cost that doesn’t show up in any national pricing guide. If you’re getting exterior waterproofing quotes, ask specifically whether the contractor has checked for subsurface conditions at your site, and how they price ledge removal if it comes up.

Frost depth. Maine’s design frost depth reaches 48 to 60 inches in northern areas. New Hampshire ranges from 36 to 54 inches depending on elevation and location relative to the mountains. Any drainage system installed above frost line will heave and fail. That means more material, more excavation depth, and more labor than a project of the same square footage would require in a warmer climate.

Other factors that commonly shift the quote:

• Foundation type: poured concrete walls are generally easier to seal than concrete block, which has mortar joints at every course
• Wall condition: active structural cracks or bowing walls add repair scope before waterproofing can be effective
• Soil type: dense clay common in parts of the Merrimack Valley retains water and places more load on drainage systems than sandy or loamy soil
• Site access: decks, mature landscaping, and driveways near the foundation raise the cost of exterior work substantially
• Basement depth: deeper basements require more material and labor to install drainage at the appropriate depth

Interior vs exterior: which one you actually need

Interior waterproofing manages water after it enters the wall. A contractor installs a channel under or along the slab perimeter and routes collected water to a sump pit and pump. It doesn’t stop water from moving through the wall, but it captures and redirects it before it damages flooring, framing, or stored belongings. Done correctly, it’s durable and effective for the vast majority of seepage complaints.

Exterior waterproofing addresses water before it reaches the wall. The contractor excavates down to the footing, applies a waterproofing membrane directly to the exterior wall surface, and installs a footing drain at the base. It’s the more thorough fix and the right approach for actively bowing or cracking walls, or for situations where the hydrostatic pressure from soil and groundwater is severe enough that interior management alone isn’t sufficient.

For most existing homes in Maine and New Hampshire with seepage as the primary complaint, contractors recommend interior systems first. Exterior waterproofing makes more sense for new construction, for homes with structural wall issues, or when the decision is being made during a major renovation that already involves excavation around the foundation.

Add-on costs to budget before signing

These items are commonly quoted separately. Knowing the price before you receive bids makes it easier to compare scopes accurately.

• Sump pump: $800 to $2,500 installed. A battery backup unit adds $300 to $800. Given the frequency of ice storms and extended outages in Maine and New Hampshire, the backup is worth factoring in from the start.
• Vapor barrier: $1,500 to $3,000 for full basement coverage. Reduces humidity transfer through the slab and is often included in full-system quotes but worth confirming.
• Window well drains: $300 to $800 per window. If water pools in the wells after heavy rain, drainage there is part of the same problem.
• Dehumidifier: $300 to $800 for a commercial-grade unit. Often recommended after waterproofing to keep humidity below 50% and prevent mold in the newly dried space.

Installing any of these at the same time as the primary system is cheaper than scheduling a return visit later.

What to check before committing to a drainage system

Not every wet basement needs a $6,000 drainage system. Two things are worth ruling out first.

Extend downspouts at least six feet from the foundation. Short downspouts deposit water right at the base of the wall, and that water has nowhere to go except in. Second, check that soil grades away from the house on all sides. If soil or lawn settles toward the foundation over time, water follows it. Correcting grading and downspouts costs a few hundred dollars and resolves a meaningful share of basement moisture complaints without any waterproofing at all.

If you do need a system, avoid the contractor who quotes by phone or pushes for a signed agreement before inspecting in person. Foundation conditions vary too much for a remote estimate to mean anything. A contractor who won’t look at the basement before quoting is pricing the job they assume you have, not the one you actually have.

How to compare quotes accurately

Collect at least three written, itemized bids. Each contractor should inspect the basement in person before quoting. When you talk with each one, ask them to explain where the water is entering from, not only what they plan to install. A contractor who explains the source is more likely to fix it.

When comparing bids side by side, match scope line by line. A lower total number that excludes the sump pump, leaves out a warranty, or doesn’t address a known crack is not lower once you add those items back in.

Confirm that each contractor carries liability insurance and is licensed for work in Maine or New Hampshire, as licensing requirements differ between the two states. Ask for written proof before signing a contract.

For local company listings and reviews, browse contractors in Portland, ME, Bangor, ME, Manchester, NH, and Concord, NH. The full basement waterproofing hub has cost tables and city listings across both states.