I am purchasing a house built into a hill with a walkout basement. I am concerned about drainage. What should I use to keep water from my basement?

For a hillside walkout, the fix that lasts is a full-perimeter interior drainage system with a sump pump, not exterior digging. That is our Forever Dry System: drain tile around the inside footing, a sump pump rated 1/2 hp per 120 feet of drain, a 12-mil wall vapor barrier, and a dehumidifier. A full basement runs $3,000 to $30,000. It comes with a guarantee that the basement stays dry for life.

Here is why a house on a hill worries people, and why the worry is fair.

When a foundation gets dug into a slope, the crew backfills around it. That backfill is loosened soil. It drains slower and holds more water than the packed ground around it. So rain and snowmelt running down the hill collect right against your walls. That is the spot water sits. Then NH winter shows up. Frost heave pushes on the wet soil, and that pressure leans on the foundation walls and works moisture through the floor wall joint where the wall meets the slab.

A walkout adds one more thing. Three sides are buried in the hill, one side is open daylight. Water moves toward the buried back corners first. So that is where you watch.

Now the fix.

You might expect us to say dig it out from the outside and tar the walls. We don’t do that, and we tell people not to pay for it. In our field experience, exterior excavation waterproofing tends to fail in about two to three years. The dirt settles, the coating cracks, and you are back to a wet wall with a five-figure hole in the yard. The durable answer is interior drainage. You manage the water once it reaches the wall instead of trying to keep the whole hillside dry forever.

So the Forever Dry System catches water at the floor wall joint, routes it through perimeter drain tile to the sump, and the pump sends it out. The 12-mil wall vapor barrier keeps wall moisture off your finished space. The dehumidifier holds the humidity down so the air does not feel like a cave. Dry for life, and the guarantee transfers if you sell, as long as no other contractor touches the work.

One add-on we tell every hillside buyer to get. A battery backup for the sump pump. A bad storm on a slope is exactly when the power tends to drop, and a dead pump during the heaviest rain is the worst time to find out. A charged backup battery can pump about a residential pool’s worth of water, roughly 15,000 to 20,000 gallons, before it needs power back. Worth it.

What you probably do not need yet: foundation repair. Drainage and structure are different jobs. If an inspector flags a bowing wall, leaning, or cracks wider than a credit card edge, that is a structural and foundation repair question (think carbon-fiber straps at $850 each or piers), and we look at it separately. Most walkout buyers come to us for water, not steel. Get the waterproofing sorted first.

What drives the price on a walkout: how many linear feet of drain the perimeter needs, how many sump pits, and whether the buried corners are already taking on water. We give you the number after a free look, not before.

If the home has a dirt or fieldstone crawl section under part of it, that is a separate scope, crawlspace encapsulation, not the Forever Dry System. And a hillside lot often holds radon in that backfill, so it is worth a test. We can fold that in too. See our radon mitigation page and our 603 guarantee.

Per the EPA, the radon action level is 4.0 pCi/L, and they say to consider fixing between 2 and 4. NH DHHS has a state radon program worth a look before you close. The DOE Building America program notes that an uninsulated foundation or crawl can give up a meaningful share of a home’s heat, which is one more reason to handle the below-grade space before you move in. And per the Insurance Information Institute, standard homeowners policies do not cover seepage from the ground, which is why you fix the cause instead of betting on a claim.

Buy the house. Just budget the basement into your offer.

Call us at 603-610-1770 or book your free inspection. We give you a quote within 24 hours, free estimate, and financing through Hearth if you want it (subject to approval, and we make nothing on it).

Related questions

Should I dig out the foundation from outside to fix a wet walkout? We don’t, and we tell people to skip it. In our experience exterior digs fail in about two to three years as the backfill settles and the coating cracks. Interior perimeter drainage to a sump is the durable fix and it carries our dry-for-life guarantee.

Do I need a backup sump pump on a hillside house? Yes. Storms on a slope are when power drops and water peaks at the same time. A charged backup battery pumps roughly 15,000 to 20,000 gallons, about a residential pool, before it needs power back. It is the cheapest insurance in the system.

What if the inspector finds cracks in the foundation wall? Drainage and structure are two jobs. Thin settling cracks often just need crack injection at $1,000 to $3,000. A wall that bows or leans is a stabilization question (carbon-fiber straps at $850 each or helical piers). We look at it and price it after we see it.

Is the buried back corner of a walkout the part that leaks? Usually. Three sides sit in the hill and water runs downslope toward the back wall, so the buried corners take it first. That is where we watch, and where the perimeter drain earns its keep.