Where It Enters Decides Everything
Down a wall, from near the top — surface water
Roof runoff discharging beside the foundation, ground that has settled to slope back toward the house, a window well acting as a bucket. This is the cheapest problem on this page and it is fixed outside, frequently for a few hundred dollars and sometimes for nothing.
A single inch of rain on a modest roof is well over a thousand gallons of water, and a downspout ending beside the wall delivers all of it to the worst possible place. Extending downspouts six feet and correcting the grade resolves a genuinely large share of the wet basements we are asked to look at.
At the floor-wall joint — hydrostatic pressure
Groundwater outside standing higher than your floor, pushed up through the joint. No coating applied to the wall can affect this, because the water is not coming through the wall. This is the misdiagnosis that costs people most, and it leaves them with a wet basement and a paid invoice.
The remedy is interior perimeter drainage: a channel around the inside of the footing that collects the water and carries it to a sump, which discharges it well away from the building. It is a real expense and on this symptom it is the thing that works.
Through a crack — the crack is the entry point
Injection seals it. Whether anything more is needed depends on what the crack is doing, which is a separate question.
On fieldstone — none of the above applies
An antique stone foundation was built to let moisture through. Sealing the inside face traps water in the stone, works at the mortar and pushes moisture into the sills above. On a Wolfeboro or Gilmanton cellar the job is managing water, not blocking it — and some damp down there is normal and always has been.
What It Costs
| Work | Typical cost | When it is the answer |
|---|---|---|
| Downspout extension & gutter correction | $0–$400 | Water down a wall; roof runoff at the foundation |
| Regrading around the foundation | $400–$1,500 | Ground slopes back toward the house |
| Window well drainage & covers | $200–$1,200 | Water around a basement window |
| Crack injection | $400–$900 per crack | Water through a stable crack |
| Partial interior drainage | $3,000–$7,000 | One or two walls affected |
| Full interior perimeter drainage & sump | $10,000–$15,000+ | Hydrostatic pressure around the footprint |
| Exterior excavation & membrane | Quoted per job | Rare, and only where interior work will not serve |
National average for basement waterproofing is around $5,236, typically $2,461–$8,196. Which is a useful number for orientation and a terrible one for budgeting, because the spread on this page is the real story.
- Diagnosis before quoting — always
- We say so when the answer is outside and cheap
- Interior drainage where hydrostatic pressure is the cause
- Fieldstone managed rather than sealed
- Written assessment with photographs
- No structural determinations we are not qualified to make
Waterproofing Questions
Will sealing the walls fix it?
Only if water is genuinely passing through the wall material, which is less common than it is sold. Water at the floor-wall joint comes from below and a coating cannot touch it. Establish where the water enters before anybody applies anything — the diagnostic does this in two minutes.
Is interior or exterior waterproofing better?
They solve different problems. Exterior excavation and membrane addresses water before it reaches the wall and is genuinely thorough — and it is also disruptive and expensive, involving digging out the perimeter of your house. Interior drainage manages water once it arrives and is considerably less invasive. For most Lakes Region basements with hydrostatic pressure, interior drainage is the proportionate answer.
My basement is only wet in spring. Do I need the full system?
You need drainage rather than sealing, but not necessarily the full perimeter. A basement dry for eleven months does not have a failed wall. Where the water appears, and on how many walls, decides whether partial drainage will serve. And do the cheap exterior work regardless — it reduces the volume arriving.
Can water damage be covered by insurance?
Groundwater seepage and surface water intrusion are commonly excluded from standard homeowner policies, which surprises people. Sudden events such as a burst pipe are usually different. Worth reading your policy before assuming, and worth asking your agent about a water backup endorsement if you have a sump.
How long does the work take?
Exterior grading and downspout work: usually a day. Crack injection: hours. Partial interior drainage: one to two days. Full perimeter drainage with a sump: typically two to four days depending on footprint and access, and it is dusty, noisy work involving breaking out a channel of concrete floor. We will tell you honestly what living with it looks like.