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Foundation Repair and Basement Waterproofing in Merrimack, NH
Merrimack's permit fee schedule lists finished basements by name, and the town's hazard plan records floods on the Souhegan, Baboosic Brook and the Merrimack River. Call (978) 800-2819 or use the form. A person reads every request and replies with what happens next.
- Free for homeowners
- Town and state rules on this page
- Souhegan River to Baboosic Brook
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Basements in Merrimack
What does the basement need?
Waterproofing & Drainage
Wet walls, seepage at the floor joint and spring water in the basement, handled with interior drains, exterior work or both.
Sump Pumps
New pits, replacement pumps and battery backups, with the discharge going somewhere your town allows.
Foundation Cracks & Repair
Leaking cracks, bowing or settling walls and failing mortar in old fieldstone, with an engineer brought in when the job is structural.
Crawl Spaces & Finishing
Damp crawl spaces sealed up, and dry basements turned into finished space with the right permits.
Not sure what it needs?
(978) 800-2819Tell us whether you're fixing water first or finishing the space, and we'll help you work out the order of the work.
Permits
Permits and rules for basement work in Merrimack
The Building and Code Enforcement Division, part of Fire and Rescue, can be reached at (603) 420-1730. Owners must have every permit before work starts, and each permit carries its own inspections (Building and Code Enforcement). Building permits are filed on the town's OpenGov portal; oil and propane fire permits are not online (Building Permit Applications).
- Building and Code Enforcement
- (603) 420-1730
- Apply online
- OpenGov
- Finished basements
- $0.68 per sq ft plus $35 application fee (effective January 1, 2025)
- Plumbing or electrical alone
- $75 each
- Re-inspection
- $50
- Work before the permit
- 100% surcharge
Finished basements are named. The fee schedule approved in the fall of 2024 and effective January 1, 2025 prices residential "Interior Alterations, Finished Basements and Renovations" at $0.68 per square foot, with a $35 non-refundable application fee, plumbing or electrical permits not tied to a building permit at $75 each, re-inspections at $50, and a 100% surcharge when work starts before the permit (fee schedule). The town's permit checklist says renovations need a building and septic application plus the gas, mechanical, electrical and plumbing permits that apply, and foundation-only work needs the building and septic application, with a sewer application where the lot is sewered (permit checklist). Egress windows, sump pumps and waterproofing aren't listed, so ask the division.
Code edition. Merrimack's code page says the 2024 New Hampshire State Building Code took effect July 1, 2026, with a concurrence period from July 1 to December 31, 2026; from January 1, 2027, all permit requests follow the 2024 codes (NH State Building Code).
Contractor rules. There's no state license for basement or home improvement contractors; the Attorney General says, "In New Hampshire, contractors do not need to be licensed," and recommends references, proof of insurance and a written contract with scope, materials, price and payment schedule before money changes hands. A deposit over half the final cost is a warning sign (NH Attorney General). Plumbers and electricians are licensed by the state, with exemptions for owners working on their own single-family homes (Mec 300; RSA 319-C). A contract over $5,000 must carry the RSA 359-G defect notice (RSA 359-G), and digging outside needs a Dig Safe ticket at least 72 hours ahead, excluding weekends and holidays (Dig Safe; RSA 374:51).
Last verified November 2026. Fees, restrictions and deadlines on this page are due for re-checking by January 2027. New England Basement Pros is a referral service. We don't pull permits or do basement work; the contractor files the permit.
Water
Where the water comes from in Merrimack
Flood history. The town's Hazard Mitigation Plan Update, adopted July 15, 2021, lists flood events in Merrimack and across Hillsborough County, including March 1936 snowmelt and rain, the Merrimack River in April 1960, ice jams in March 1977 that flooded five homes on the Souhegan, Pennichuck Brook in May 2001, up to 14 inches of rain from May 12 to 23, 2006, and declared disasters in April 2007, September 2008 and March 2010, when an undersized culvert flooded Johnson Corner (Hazard Mitigation Plan). The plan itself doesn't discuss basement flooding or groundwater. Merrimack has been in the National Flood Insurance Program since July 16, 1979.
Merrimack River
A flood hazard waterway in the 2021 plan, which records its April 1960 flood.
Souhegan River
Ice jams in March 1977 flooded five homes along it, according to the plan.
Baboosic Brook
Named with the two rivers as a flood hazard waterway; Blood, Stony and Mill Brooks are listed too.
Island Drive
The plan calls this area "particularly prone to flooding."
Flood zones. Zoning's Flood Hazard Conservation District covers FEMA's special flood hazard areas from the Hillsborough County flood study and maps dated September 25, 2009 (2024 zoning ordinance). For your own address, use FEMA's Flood Map Service Center.
Sewer, septic and the pump outlet. The 2013 Sewer Master Plan says town sewer serves about a third of the community and "a significant portion of Merrimack is not currently served by public sewer" (Sewer Master Plan). Homes within 200 feet of the sewer must connect, a residential connection is $2,000, and "A sanitary check valve IS required" (Sewer Connection Requirements). State rules keep sump pumps and foundation drains out of any public sewer (Env-Wq 704), and the town's 2023 illicit discharge ordinance says illicit connections to the storm drain system, which includes streets, catch basins, curbs, gutters and ditches, are prohibited (Chapter 168). The town's sewer use chapter has its own sections on surface runoff, groundwater and unpolluted water (Chapter 158); ask the town where your discharge line may go before it's installed.
Wetlands. Zoning includes a Wetlands Conservation District (ordinance revised September 12, 2024), and the Conservation Commission reviews state dredge-and-fill permits (Conservation Commission). Check where the district lines fall before an outside drain or regrading goes near a wet area, and disturbing more than 20,000 square feet may bring in the town's stormwater standards (Stormwater).
Merrimack's homes
About a third of the town on sewer
We didn't find year-built figures for Merrimack's houses on an official town page. What the town's plans do make clear is the split between the sewered third and the rest of town on septic (Sewer Master Plan). That split decides a lot about a wet basement: on a septic lot the sump line has to end somewhere on the property, while a sewered house also needs its own sewer line kept tight and, on a new connection, a check valve.
None of the districts in the 2024 zoning ordinance is a historic district, and the town's Heritage Commission page doesn't name one (Heritage Commission), so a bulkhead or window well goes through ordinary building review.
Radon
Radon in Merrimack basements
No Merrimack-level radon figure is published, and the state's August 2023 data brief gives no median for Hillsborough County. Statewide, about 37% of 32,747 tested homes, tested from 2007 to 2021, were at or above 4 pCi/L (NH radon data brief). Finishing a basement is a natural time to test: the state says to test in the lowest livable area, EPA recommends fixing at 4 pCi/L or more, and free kits are available from the NH Radon Program at (603) 271-1708 (testing your home).
FAQ
Merrimack basement questions
Does finishing a basement in Merrimack need a building permit?
Yes. The town's fee schedule, effective January 1, 2025, lists "Interior Alterations, Finished Basements and Renovations" at $0.68 per square foot, plus a $35 non-refundable application fee. Starting work before the permit adds a 100% surcharge.
Does my house need a check valve on the sewer?
For a new connection, yes. The town's sewer connection requirements say "A sanitary check valve IS required," and homes within 200 feet of the sewer must connect.
Which parts of Merrimack flood?
The 2021 Hazard Mitigation Plan names the Merrimack and Souhegan Rivers and Baboosic Brook as flood hazard waterways, along with Blood, Stony and Mill Brooks, and calls the Island Drive area particularly prone to flooding.
Where does sump pump water go if my house is on septic?
Not into the septic system or the sewer. State rules keep sump pump and foundation drain water out of public sewers, and Merrimack prohibits illicit connections to its storm drains. Ask the Building and Code Enforcement Division where your discharge line should end.
What does it cost me to use New England Basement Pros?
Nothing. Asking is free for homeowners; the contractor prices the job, and the price and contract are between you and them.
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