Basement finishing on the South Shore runs $45 to $95 per square foot, putting a 1,000-square-foot basement between roughly $45,000 and $95,000. But that per-square-foot figure is the finish work only — and the four line items it usually excludes are where budgets actually break. US ProPaint & Renovation handles waterproofing, egress, radon and the bathroom plumbing in house.
By JR Reis, Owner & President · Last updated October 2026
Market ranges, not quotes — every basement we price gets walked first.
| Finished area | Basic open plan | Standard, divided rooms | Premium with bath |
|---|---|---|---|
| 600 sq ft | $27,000 – $36,000 | $33,000 – $45,000 | $45,000 – $57,000 |
| 800 sq ft | $36,000 – $48,000 | $44,000 – $60,000 | $60,000 – $76,000 |
| 1,000 sq ft | $45,000 – $60,000 | $55,000 – $75,000 | $75,000 – $95,000 |
| 1,200 sq ft | $54,000 – $72,000 | $66,000 – $90,000 | $90,000 – $114,000 |
National guides quote $30 to $75 per square foot. The South Shore sits above that because Greater Boston trade labour runs 20 to 35% over the national average — a real gap, not a markup.
Here’s the part worth reading twice. When a contractor quotes you a per-square-foot number, it almost always covers framing, insulation, drywall, ceiling, flooring, trim, lighting and paint. It usually does not include:
Those four can add $15,000 to $45,000 to a project whose headline number looked settled. Ask any bidder which of them are in and which are out, in writing, before comparing quotes — otherwise you’re comparing numbers that describe different jobs.
| Category | Share of budget | Typical on a 1,000 sq ft basement |
|---|---|---|
| Systems — electrical, plumbing, HVAC | 30 – 40% | $18,000 – $35,000 |
| Framing, insulation, drywall | 25 – 30% | $15,000 – $27,000 |
| Flooring | 10 – 15% | $6,000 – $13,000 |
| Trim, doors, paint | 10 – 15% | $6,000 – $13,000 |
| Ceiling | 5 – 10% | $3,000 – $9,000 |
| Permits and project management | 5 – 10% | $3,000 – $9,000 |
Systems are the surprise. Most homeowners budget for what they’ll see — flooring, finishes, a nice ceiling — and the single largest share goes to things that end up behind drywall. A basement needs dedicated circuits, often a panel upgrade, HVAC capacity that the existing system was never sized for, and plumbing that may have to run uphill.
Which choices add the most, in order of impact:
| Choice | Added cost |
|---|---|
| Full bathroom | $12,000 – $25,000 |
| Three-quarter bathroom | $8,000 – $15,000 |
| Waterproofing and drainage | $2,000 – $8,000 |
| Egress window (cutting and well) | $3,800 – $8,400 |
| HVAC extension or dedicated system | $2,000 – $8,000 |
| Wet bar or kitchenette | $3,000 – $6,000 |
| Radon mitigation | $1,400 – $2,800 |
| Electrical panel upgrade | $2,000 – $4,500 |
| Drywall ceiling instead of drop ceiling | $2,000 – $5,000 |
A bathroom is almost always the largest discretionary item on a basement budget, and the reason is plumbing rather than fixtures.
A basement sits below the main sewer line in most houses. Waste can’t drain by gravity from a point lower than the pipe it’s draining into. So a basement bathroom needs one of two solutions, and which one you need is determined by the elevation of your main line where it leaves the building — not by preference.
Option A: break the slab and run a gravity drain below grade. Adds $4,000 to $8,000. Possible when the main sewer line exits low enough that new drainage can still fall into it. This is the better outcome when it’s available: no pump, no motor, nothing with a service life, and nothing that makes noise at 2am.
Option B: an above-slab ejector pit or up-flush system. Adds $2,500 to $5,000. Required when the main line sits above the slab. A sealed basin collects waste and a pump lifts it to the drain. It works reliably, but it’s mechanical — it needs power, it has a service life, and it’s audible.
We do both, which matters here more than it sounds. A contractor who only does one will tend to find that one is what your house needs.
Two things to check before you budget:
The elevation question gets answered on site with a measurement. Any contractor quoting a basement bathroom over the phone is guessing at the most expensive variable in the project.
$2,000 to $8,000 for typical work — an interior perimeter drain, a sump, and vapour control. Where there’s significant water intrusion or a high water table, it climbs from there.
This is the line item people try to cut, and it’s the one that destroys everything built on top of it. Framing over an unresolved moisture problem doesn’t give you a dry basement; it gives you a hidden one, with mould growing inside a finished wall. Our basement remodeling guide covers the three distinct moisture mechanisms in New England basements and the plastic-sheet test you can run yourself in an afternoon — worth reading before you set a budget, because a basement that has never had a visible puddle can still be pushing vapour through the concrete.
Where we open a wall and find existing growth, remediation happens with the same crew — we hold Certified Residential Mold Inspector (CRMI0000036883) and Certified Mold Remediator (CMR0000036885) licences.
Finishing a basement costs roughly a quarter to a third of what an addition costs per square foot. You already own the floor, the walls and the roof.
| Basement finishing | Addition | |
|---|---|---|
| Cost per square foot | $45 – $95 | $200 – $300+ |
| Counts as living square footage | No | Yes |
| Zoning and setback review | No | Yes |
| Site disruption | Contained | Significant |
| Typical timeline | 8 – 14 weeks | Considerably longer |
But cheaper per foot is not the same as better value, and this is where the honest answer lives. Below-grade space is excluded from Gross Living Area on an appraisal no matter how well it’s finished — which means a basement is cheaper space that is also valued lower. An addition costs three to five times as much per foot and counts in full.
The full explanation, including why an egress window and a bedroom don’t change this despite what several cost guides claim, is in our basement remodeling guide.
The practical read: if you need living space and the budget is the constraint, the basement wins easily. If you’re building primarily for resale value per dollar spent, the maths is closer than the per-square-foot gap suggests.
A basement budget breaks in the places where trades hand off to each other. We self-perform the parts that usually get subcontracted, which is why the quote you get is the one you pay:
Plus 1,000+ completed projects, Massachusetts Contractor License 186517, lead-safe certified, fully insured, with free estimates and financing.
Where we work: Weymouth, Hingham, Braintree, Quincy, Hull, Cohasset, Scituate, and across the South Shore.
Full scope is on our finished basement page. Finished work is in the gallery.
What does it cost to finish a basement on the South Shore?
$45 to $95 per square foot, so roughly $45,000 to $95,000 for 1,000 square feet depending on finish level and whether a bathroom is included. That figure covers framing, insulation, drywall, ceiling, flooring, trim and paint. Waterproofing, an egress window, radon mitigation and a bathroom are usually quoted separately and can add $15,000 to $45,000.
Which choices add the most to basement finishing cost?
A full bathroom is the largest at $12,000 to $25,000, followed by waterproofing at $2,000 to $8,000, an egress window at $3,800 to $8,400, and HVAC extension at $2,000 to $8,000. Overall, systems — electrical, plumbing and HVAC — absorb 30 to 40% of a typical budget, which is more than most homeowners expect for work that ends up behind drywall.
Is adding a basement bathroom worth the extra spend?
It depends on how the space will be used. A basement without a bathroom is a rec room; with one it functions as a real second living level, and it’s effectively required if anyone will use the space for guests or as a bedroom. The cost hinges on drainage: breaking the slab for a gravity drain adds $4,000 to $8,000, while an above-slab ejector system adds $2,500 to $5,000. If there’s an existing rough-in stubbed in the slab, a three-quarter bath can come in at $5,000 to $8,000.
How much does moisture control add to the budget?
$2,000 to $8,000 for an interior perimeter drain, sump and vapour control, more where there’s significant water intrusion. It is the one line item that should never be cut, because framing over an unresolved moisture problem conceals it inside a wall rather than solving it.
Basement finishing or an addition: which costs less per square foot?
Basement finishing at $45 to $95 per square foot runs roughly a quarter to a third of an addition at $200 to $300 or more, because the floor, walls and roof already exist. The trade-off is that below-grade space is excluded from Gross Living Area on an appraisal while an addition counts in full — so the basement is cheaper space that is also valued lower.
Why do basement quotes vary so much between contractors?
Usually because they cover different scopes. The per-square-foot number most contractors lead with is the finish work only. Ask each bidder in writing whether waterproofing, an egress window, radon mitigation and a bathroom are included or excluded, and most of the spread between quotes disappears.
How much does an egress window cost on the South Shore?
$3,800 to $8,400 installed, because it involves cutting the foundation and excavating a window well rather than swapping a window. It’s required for any legal below-grade bedroom, and it’s far cheaper to do during a finish project than to retrofit afterwards.
US ProPaint & Renovation
Adress:175 Derby St STE 4 Hingham, MA 02043
Phone: +1 (617) 922-6305
Toll Free: +1 (800) 964-0717
Email: office@uspropaint.com
Massachusetts Contractor
License 186517 ·
Lead-Safe Certified · Mold Inspector CRMI0000036883 · Mold Remediator CMR0000036885
Serving Weymouth, Hingham, Braintree, Quincy, Hull, Cohasset, Scituate, Norwell and the South Shore.
