In New Hampshire, any finished basement with a bedroom needs an egress window. Under the building code NH uses, the opening has to give at least 5.7 square feet of net clear space, stand at least 24 inches tall and 20 inches wide, and sit with its sill no more than 44 inches above the floor.
That one rule decides a lot about your basement project. If you are turning your basement into a real bedroom, an office someone could sleep in, or a guest suite, the code does not treat it like storage anymore. It treats it like a place a person could be asleep when something goes wrong, so it wants a second way out.
We are 603 Basement Solutions. We dry out and finish basements across the New Hampshire Seacoast and Rockingham County, from Exeter and Stratham to Portsmouth, Dover, and Hampton, plus southern NH and into Maine and Massachusetts. This guide walks through exactly what the egress rule says, where homeowners get tripped up, and what cutting one of these openings really involves in an older NH foundation. The cost and the exact warranty on your job get confirmed in writing after a free inspection, so this stays about the code, not a quote.
What is an egress window, and when does code require one?
An egress window is a window big enough to climb out of in an emergency, and big enough for a firefighter in full gear to climb in. That is the whole idea. “Egress” just means a way out.
The building code requires one in a few specific spots. Under the International Residential Code, the rule reads: “Basements, habitable attics and every sleeping room shall have not less than one operable emergency escape and rescue opening.” So two things in a basement project pull the trigger:
- You are finishing a basement that will contain a sleeping room (a bedroom).
- You are adding any new bedroom, basement or not.
If your finished basement is a media room, a gym, or an office with no bed and no closet meant for sleeping, the bedroom-specific rule is not the thing forcing an egress window. But the moment you call a room a bedroom, or build it so it functions as one, the code wants that escape opening. This is the single most common reason a finished basement project in NH needs an egress window, and it is the one homeowners discover late, after the walls are already framed.
A door to a walkout or a bulkhead can satisfy the “way out” in some layouts. But most NH basements are fully below grade with no walkout, so the practical answer for a basement bedroom is a code-sized egress window set into the foundation wall with a window well outside it.
If you are mapping out the whole project, our basement finishing page covers how a finished basement comes together, and what basement finishing consists of breaks down the steps of turning the space into usable living area.
New Hampshire egress window code: the exact numbers
Here are the minimums, straight from IRC Section R310, the emergency escape and rescue requirement. New Hampshire’s adopted residential code is the New Hampshire Residential Code 2021, based on the 2021 IRC. These same R310 dimensions are unchanged from the 2018 edition, so the numbers below are the ones that apply across NH.
| Requirement | Minimum | Notes |
|---|---|---|
| Net clear opening area | 5.7 sq ft | 5 sq ft is allowed for a grade-floor opening |
| Net clear opening height | 24 inches | The clear vertical space you can actually pass through |
| Net clear opening width | 20 inches | The clear horizontal space you can actually pass through |
| Sill height above floor | 44 inches max | Measured from the finished floor to the bottom of the opening |
| Operation | From the inside | No keys, no tools, no special knowledge |
“Net clear opening” is the important phrase. It is not the size of the window unit or the size of the rough opening. It is the actual hole you can crawl through once the window is open, with the sash out of the way. The frame, the track, and any hardware do not count toward it.
The 44-inch sill rule matters in a basement because a basement floor sits low. If the bottom of the window is too high off the floor, a person, especially a child, cannot reach it to get out. That ceiling on sill height is why basement egress windows usually sit lower in the wall than a normal basement window, and why the well outside often has to be dug deeper.
Why the minimums are a trap
Here is where people order the wrong window. The minimum height is 24 inches and the minimum width is 20 inches, but a window that is only 24 by 20 does not pass.
Do the math. 24 inches times 20 inches is 480 square inches, which is 3.33 square feet. The code wants 5.7 square feet of net clear opening. So hitting only the two linear minimums leaves you almost 2.4 square feet short of the area rule.
The window has to satisfy all three at once: the area and the minimum height and the minimum width. To get to 5.7 square feet while holding 24 inches of height, you need more than 34 inches of width. To get there while holding 20 inches of width, you need more than 41 inches of height. A real egress unit is bigger than the bare minimums make it sound. That is why an egress window is its own product and its own sized opening, not just a slightly larger basement window.
One more rule that is easy to miss: the opening must be operable from the inside without keys, tools, or special knowledge. A window you have to unscrew, or one painted shut, or one that needs a removable crank stored somewhere does not count, no matter how big it is. Someone has to be able to get it open in the dark, fast.
Window wells: what a below-grade opening also needs
Because a basement floor sits below grade, the egress opening almost always pokes out below the level of the yard. That means you need a window well, and the well has its own code.
- Size: The well must give at least 9 square feet of horizontal area, with a minimum horizontal projection and width of 36 inches. In plain terms, the well has to stick out at least 3 feet from the foundation and be at least 3 feet wide, so a person has room to stand up and climb.
- A way up: If the well is deeper than 44 inches, it needs a permanently affixed ladder or steps. A deep well with no ladder is a pit you can fall into and not climb out of, so the code closes that gap.
- Drainage (the NH part): This is where Seacoast homes get into trouble. A window well is a hole dug right against your foundation, below grade. On the wet NH Seacoast, with a high water table, a well with no drainage becomes a bathtub. Every rain fills it, and the water sits right against your brand-new egress window and the finished room behind it. A proper well drains, usually with a gravel base and a drain tied into the perimeter or footing drain or a sump. Skip that, and you have funneled water straight into the room you just paid to finish.
We will come back to drainage, because on the Seacoast it is not a detail. It is the difference between a finished basement that stays dry and one that floods through its newest opening.
Cutting an egress opening in an older NH foundation
A lot of New Hampshire housing is not new. Plenty of homes around Exeter, Kingston, and the older Seacoast towns have fieldstone or rubble foundations, and many others have thick poured-concrete walls. Cutting a code-sized egress opening into one of those is real structural work, not a trim-out.
Here is why. You are removing a chunk of a wall that is holding up the house and holding back the soil outside. You cannot just saw a rectangle and drop a window in. The opening needs proper structural support over the top, a header or lintel sized to carry the load that used to run through that section of wall. In a fieldstone or rubble wall, that is delicate work, because the wall is a stack of stones, not a monolithic slab, and you have to support it as you open it up.
Then there is frost. New Hampshire freeze-thaw and frost heave will work on anything below grade that is not detailed for it. A shallow or poorly drained window well can heave in winter and crack, and that movement can telegraph into the new opening. The well and the opening both have to be built for frost movement, with the right depth and drainage, or the work that looked fine in October cracks by spring.
None of this is meant to scare you off an egress window. It is meant to set the expectation: a basement egress window in an older NH foundation is a planned, engineered cut with structural support and drainage, done by people who have opened these walls before. It is not a weekend job.
What does it cost? An egress window installation, including cutting the opening, the header, the well, and drainage, generally runs from $8,000 to $15,000, depending on your foundation type and how deep the well has to go. Your exact number gets confirmed in writing after a free inspection.
Dry the basement first
Here is the order that saves people money: dry the basement before you frame a bedroom around a new egress window.
A finished room built around a leak is wasted money. If water is already getting in through the slab, the wall joints, or hydrostatic pressure under the floor, that water does not stop just because you hung drywall. It rots the new framing, ruins the new flooring, and grows mold behind the finished walls where you cannot see it.
That is what our Forever Dry System is for. It is a full-perimeter interior drain, a sump pump, a wall vapor barrier, and a dehumidifier, working together to keep the space dry for good. We put that system in first, get the basement dry and keep it that way, and then frame the bedroom and set the egress window into a space that is actually ready to be lived in. Build it in the other order and you are betting your new bedroom on a basement that was never dried out.
Test for radon while you are down there
Any time you are cutting a new below-grade opening and finishing a basement, it is a good moment to test for radon. Radon is the number one cause of lung cancer among non-smokers, and the second leading cause of lung cancer overall, responsible for about 21,000 lung cancer deaths every year, according to the EPA.
Radon is an odorless, invisible radioactive gas that comes up out of the soil and rock. It enters a home through small cracks or holes in the foundation and collects in the lowest level, which is exactly where your new finished basement is. The CDC notes that radon levels are often higher in basements and lower levels of a home. The EPA flags 4 pCi/L as the level to act on.
Parts of New Hampshire and New England sit on granite bedrock, which is associated with higher radon potential. So a basement-finishing project, the moment when you are already opening the floor and walls and turning the lowest level of the house into a bedroom, is the natural time to test. If the level comes back high, it gets mitigated before the room is finished, not after. 603 is a state-certified radon contractor, so testing and mitigation can be part of the same project.
Permits and your town
One thing this guide cannot do is give you a single statewide answer to your permit question, and you should be suspicious of anyone who tries.
New Hampshire’s state building code is enforced locally, town by town. NH adopts the 2021 IRC statewide, so the R310 egress rules in this guide apply to a finished basement bedroom anywhere in the state. But your own town’s building department is who enforces it, who issues the permit, and who inspects the work. Towns can also adopt stricter local ordinances on top of the state code.
Finishing a basement bedroom and cutting an egress opening typically requires a building permit and an inspection. The right move is to call your own town’s building department before the work starts, whether that is Exeter, Portsmouth, Dover, Hampton, Stratham, Salem, or Manchester in southern NH. Ask what they require for a finished basement bedroom and an egress window, and pull the permit. We are used to working through that process with NH towns, and we would rather do it right and pass inspection than redo a wall.
Frequently asked questions
Does every finished basement need an egress window?
No. The egress rule is triggered by a sleeping room. A finished basement used as a media room, gym, or office without a bedroom is not forced to have an egress window by the bedroom rule. The moment you build a basement bedroom, or any new bedroom, the code requires at least one emergency escape and rescue opening.
What is the minimum size for a basement egress window in New Hampshire?
Under IRC R310, which NH adopts, the opening needs a net clear area of at least 5.7 square feet (5 square feet is allowed for a grade-floor opening), a clear height of at least 24 inches, a clear width of at least 20 inches, and a sill no more than 44 inches above the floor. Because the minimum height and width alone only add up to 3.33 square feet, a real egress window is larger than those two numbers suggest.
Do I need a window well, and how big does it have to be?
If the opening is below grade, which most basement egress windows are, you need a window well. The well must give at least 9 square feet of horizontal area, with a minimum projection and width of 36 inches. If the well is deeper than 44 inches, it needs a permanently affixed ladder or steps. On the wet NH Seacoast, the well also has to drain, or it collects water against your foundation and your new window.
Can you cut an egress window into a fieldstone or concrete foundation?
Yes, but it is structural work. Cutting a code-sized opening into a fieldstone, rubble, or thick concrete foundation wall means removing a load-bearing section and adding proper structural support, a header or lintel, over the new opening. It has to be detailed for NH frost movement and drainage too. This is a planned, engineered job, not a quick saw cut.
Do I need a permit for a basement bedroom and egress window in NH?
In most cases, yes. New Hampshire enforces its building code locally, so finishing a basement bedroom and cutting an egress opening typically requires a permit and an inspection from your town’s building department. Call your own town, whether that is Exeter, Portsmouth, Dover, or another, before the work starts, since towns can add stricter local rules.
Should I test for radon when finishing my basement?
It is a good idea. Radon is the second leading cause of lung cancer overall and is often highest in the lowest level of the home, which is your new finished basement. Parts of NH sit on radon-prone granite bedrock. Since you are already opening the floor and walls, it is the natural time to test, and if the level is high, mitigate it before the room is finished. 603 is state-certified for radon testing and mitigation.
Get a free inspection
Thinking about a basement bedroom and not sure about the egress window or whether your foundation can take the cut? We will come look, for free.
You get a free inspection and a free written estimate, with your quote within 24 hours. No pressure, no treating you like just another number. We dry the basement first with the Forever Dry System, handle the egress opening and the permit step with your town, and frame a space that passes inspection and stays dry. We are insured, and any warranty that applies to your job is spelled out in writing on your estimate.
Ready to experience your dream basement? Call 603 Basement Solutions at (603) 610-1770 and we will get you on the schedule.
You can also read up on our egress window installation and, if you are budgeting the whole project, the average cost of basement finishing.
