Portsmouth is a small city on a tight footprint, and square footage is not cheap here. A finished basement is one of the only ways to add real living space without touching the footprint of the house, and it is why finishing calls in this city are usually about a family room, an office, or a guest suite rather than a bar or a theater.
What it costs to finish a basement in Portsmouth
Cost depends on square footage, whether you want a bathroom, and how much of the mechanical work, wiring, plumbing rough-in, is starting from scratch. Most jobs run 4 to 24 weeks depending on scope. We pull the permit and run it as a single crew from framing to final walkthrough, rather than handing the job between subcontractors.
The one rule that is not negotiable
We do not finish a basement with an unresolved water problem behind the wall. If your basement has ever taken on water, that gets fixed first, waterproofing before finishing, always. Framing and drywall over a wall that is still wet just hides the problem until it comes back through the new finish, and by then it is a bigger job than it needed to be.
If your basement is dry and has stayed dry, we will say so and move straight to finishing. If we are not sure, we will tell you that too, and check before we start framing anything.
What finishing actually involves
We hold framed walls off the foundation rather than nailing them flat against it, use pressure-treated bottom plates, and insulate with material that will not hold water against the wall if there is ever a small leak. If your basement will include a bedroom, a code-compliant egress window is part of the plan, we confirm the exact requirement with your town before we frame anything, since it varies by jurisdiction and we are not going to guess at a number that could be wrong for your specific house.
Frequently asked questions
Can you finish my basement and waterproof it at the same time?
Yes, and for a basement with an active water problem, that is the right order to do it in rather than two separate projects months apart.
Do I need a permit?
Yes, for a basement finishing project in New Hampshire. We pull it as part of the job.
How long before the space is usable?
Most jobs run 4 to 24 weeks depending on scope. A single room addition is on the shorter end; a full basement with a bathroom and multiple rooms runs longer.
What if you find a problem once the walls are open?
We will stop and tell you before doing anything else. That has happened, and it is always cheaper to deal with it while the wall is already open than to find it later.
What a recent customer said
From start to finish a full 5/5 star experience. When it came time for renovation, Chris and Ray and his team did a really fantastic job imagining and then piecing everything back together. It looks better than it did before the floods first ruined our finished basement. They took the time to walk us through everything at the end, and couldn’t have been more on top of their game. Everyone at 603 has been a joy to work with, and we’re so grateful to them for their immaculate work in setting our home up so well for the coming years.
Emily Cooper, 5 stars, Google review
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Sources: timeline and process figures per the founder-confirmed rate sheet. Review quoted from a public 603 Basement Solutions Google review, condensed for length.
Common questions about basement finishing
Portsmouth basement finishing — local context
Finishing a Portsmouth basement runs $30,000 to $200,000 with 603, and most jobs take 4 to 24 weeks start to finish. If you want a bedroom down there, the code matters. New Hampshire enforces the 2021 International Residential Code, and IRC Section R310 says any basement and every sleeping room needs an emergency escape opening of at least 5.7 square feet, 24 inches tall and 20 inches wide. That usually means an egress window ($8,000 to $15,000), and we install it before we frame. We pull the building permit ourselves through the City of Portsmouth Inspection Department at City Hall, 1 Junkins Avenue (603-610-7243), so you never chase paperwork. Portsmouth is the only city in Rockingham County and the Seacoast's seaport, so the water table runs high and the coastal humidity is real. We dry the space first, then one 603 crew finishes it. See how we finish basements.
What a recent customer said
I worked directly with the owner chris pagliccia and I couldnt be happier with my experience. They completed multiple projects for us including a basement demo, floor leveling, support beams, and lastly finishing turning the unfinished basement into an inlaw apartment. The project in its entirety took 6 months but throughout the entire thing they communicated well and we didn't spring on us a single "Surprise bill". Great company. — Moises Estrada
Frequently asked questions
Do I need an egress window to finish a basement bedroom in Portsmouth?
Yes. New Hampshire enforces the 2021 International Residential Code, and IRC Section R310 requires any basement and every sleeping room to have an emergency escape and rescue opening of at least 5.7 square feet, with a 24-inch minimum height and 20-inch minimum width. If your plan includes a bedroom, we install an egress window ($8,000 to $15,000) before we frame so it passes inspection.
Who pulls the building permit for a Portsmouth basement finishing job?
We do. 603 pulls the building permit through the City of Portsmouth Inspection Department at City Hall, 1 Junkins Avenue (603-610-7243), which reviews and approves the building, electrical, plumbing, and mechanical plans. You do not have to file anything yourself.
Is finishing a basement worth it in Portsmouth?
It tends to add real value here. The median value of an owner-occupied home in Portsmouth is $688,500 (Census Bureau ACS 2024 5-year estimate), well above the New Hampshire median of $402,500, so the finished square footage you add carries more weight than it would in an average town. Finishing with 603 runs $30,000 to $200,000 and takes 4 to 24 weeks.
