# Wet Basement Repair in Greater Boston: Fixes & Costs

Page: https://magnoandco.com/blog-wet-basement-repair-greater-boston

> Wet basement repair in Greater Boston: why old Somerville homes leak, fixes from gutters to waterproofing, national costs and engineer red flags.

Home Care & Safety

## Wet basement repair in Greater Boston: causes and fixes, from cheap to expensive

Wet basement repair in Greater Boston: why old Somerville homes leak, fixes from gutters to waterproofing, national costs and engineer red flags.

**Mateus Magno**
Licensed Construction Supervisor · October 26, 2026 · 3 min read

Quick answer

Most wet basements in Greater Boston are fixed from the outside in: clean gutters and extend downspouts, regrade so soil slopes away, then add an interior drain and sump pump if water still gets in. National cost guides put interior waterproofing at $6,000 to $12,000 and exterior waterproofing at $10,000 to $18,000; Greater Boston usually runs higher.

Wet basement repair in Greater Boston should start with the cheapest fix that could work, not the biggest contract a salesperson can write. In old Somerville and Cambridge houses, a lot of water problems come from the roof and the yard, not the foundation itself.

Here is how I diagnose a wet basement, the fixes in order of cost, and when you need an engineer instead of a contractor.

## Wet basement repair starts with the cause

- **Roof water.** Clogged gutters and short downspouts dump water right at the foundation.
- **Grading.** Over a century, yards settle and patios tilt back toward the house.
- **Old foundations.** In my experience, many triple-deckers and two-families sit on fieldstone or brick foundations with mortar that has washed out over the years.
- **High groundwater.** A Cambridge DPW [stormwater study of the Concord-Alewife area](https://cambridgema.gov/~/media/Files/publicworksdepartment/stormwatermanagement/ConcordAlewifeStormwaterManagement.pdf) found groundwater generally within about 3 feet of the surface there, with poorly draining soils.
- **Sewer backups and flooding.** Somerville's [Flood Ready page](https://www.somervillema.gov/departments/programs/flood-ready) warns that street flooding can push sewage back up into basements, and that the city also faces Mystic River flooding during large coastal storms.

## Step 1: gutters and downspouts (cheapest)

The [EPA](https://www.epa.gov/mold/brief-guide-mold-moisture-and-your-home) lists cleaning and repairing gutters as a basic moisture control step. I clean them, check the pitch and extend every downspout well away from the house. It takes an afternoon and, surprisingly often, solves the problem on its own. [HomeGuide's national cost guide](https://homeguide.com/costs/basement-waterproofing-cost) puts replacing downspouts at **$220 to $625** as a national average.

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## Step 2: fix the grading

The Massachusetts version of the code, in its [Chapter 4 amendments](https://www.mass.gov/regulations/780-CMR-tenth-edition-residential-chapter-4-foundations-amendments), says lots must drain water away from foundation walls, with ground falling at least **6 inches within the first 10 feet**. It also says grading must not flood or damage a neighbor's property. HomeGuide puts regrading at **$1,000 to $5,000** as a national average.

On tight Somerville lots, I often re-pitch a walkway or patio rather than regrade a yard that does not exist.

## Step 3: interior drain and sump pump

If water still comes through the wall-floor joint, an interior perimeter drain feeding a sump pump is usually the next step. HomeGuide lists these **national averages**:

| Fix | National average |
| --- | --- |
| Sump pump | $600 to $2,500+ |
| Interior French drain | $4,000 to $17,000 |
| Interior waterproofing, total | $6,000 to $12,000 |
| Exterior waterproofing, total | $10,000 to $18,000 |

Greater Boston usually runs higher. In Somerville, the Engineering Division may review any **new or existing sump pump or foundation drain**, per the City's [Engineering permits brochure](https://s3.amazonaws.com/somervillema-live/s3fs-public/engineering-permits-brochure.pdf). Where the pump discharges matters, so plan it with the permit. I also like a dedicated circuit and a battery backup, because the storms that flood basements often knock out power too.

If your basement has a floor drain, toilet or shower, the City says you may need a professional plumber to install a backflow preventer.

## Step 4: exterior waterproofing (most expensive)

Digging down to the footing, waterproofing the wall and installing a footing drain is the most complete fix and the most disruptive. Where a high water table is known, the [2021 IRC](https://codes.iccsafe.org/content/IRC2021P2/chapter-4-foundations) requires foundation walls around below-grade space to be **waterproofed**, not just dampproofed, and it calls for foundation drains around masonry foundations that enclose habitable space. On a triple-decker lot with a driveway on one side and a neighbor three feet away on the other, access alone can drive this price.

## When you need a structural engineer

- Walls that bow inward, or horizontal cracks in block or poured walls.
- Stones loose or falling out of a fieldstone wall.
- Doors and floors upstairs going out of level quickly.
- Plans to lower the basement floor or dig near the footings.

These are structure questions first and water questions second. I bring an engineer in before quoting, and the engineer's repair plan becomes the scope we price.

**Builder's tip:** Go down to the basement during a hard rain with a flashlight and your phone. Video where the water shows up: one corner, along a wall, or up through the floor. That clip tells me more than any sales inspection and usually points to the cheap fix.

## Wet basement now, finished basement later

A dry basement is step one of any basement project. Once it stays dry through a spring, see my guides to [egress windows](https://magnoandco.com/blog-egress-window-requirements-massachusetts) and [basement apartment rules](https://magnoandco.com/blog-basement-apartment-rules-massachusetts). Every house is different, so I give a written line-item budget after a walkthrough.

## Need a hand?

Tired of a damp basement in Somerville, Cambridge or Medford? [Book a free walkthrough](https://magnoandco.com/contact). I will trace where the water comes from and send a written line-item budget, usually within 48 hours.

## Frequently asked questions

How much does wet basement repair cost?

National cost guides put interior waterproofing at $6,000 to $12,000 and exterior waterproofing at $10,000 to $18,000. Simple fixes like downspout extensions or regrading cost far less, and Greater Boston prices usually run higher than national averages.

What is the most common cause of a wet basement?

In my experience in old Greater Boston houses, roof water and grading cause most problems: clogged gutters, short downspouts and soil or patios sloping toward the house. Fix those before paying for drains or waterproofing.

Do I need a permit for a sump pump in Somerville?

Somerville's Engineering Division may review any new or existing sump pump or foundation drain as part of a building permit, so check with the City before installing one.

When should I call a structural engineer about my basement?

Call an engineer if walls bow, you see horizontal cracks, stones are falling out of a fieldstone wall, or you plan to lower the floor or dig near the footings.

**Planning work on your home?** See [everything I do](https://magnoandco.com/services), [how I price work](https://magnoandco.com/pricing) and [the towns I work in](https://magnoandco.com/areas).

**Good to know:** this article is general information, not legal or engineering advice. Rules change and every property is different — confirm the details for your home with your city's building department, or [ask me](https://magnoandco.com/contact). See our [Terms & Disclaimers](https://magnoandco.com/terms).

**About the author**

Mateus Magno founded Magno & Co in 2020. He is a licensed Massachusetts Construction Supervisor (CS-123658), registered Home Improvement Contractor (HIC #220484) and certified Lead-Safe Renovator Supervisor who has renovated and managed over $5 million in projects across Greater Boston.

[More about Mateus →](https://magnoandco.com/about)

Keep reading

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