Planning a Home Addition in Bismarck or Mandan: Permits, Footings and Budget
Who this is for: Bismarck and Mandan homeowners who are running out of room and want to understand permits, foundations, budget and timing before they talk to a builder.
The short answer
An addition in Bismarck needs a building permit, a lot survey and a set of plans, and its footings have to be designed for the city's required frost depth of 48 inches below finished grade. The cost depends far more on what you're adding (a bump-out, a bedroom, a garage) and what sits under it than on square footage alone, which is why we don't quote a per-square-foot number without seeing the house.
One more thing to know up front: a contractor's North Dakota license class limits the size of a single project they can take on. HHI holds a Class D license, which covers projects up to $100,000 per job, so we focus on additions that fit within that limit. Our page on home additions in Bismarck-Mandan explains how we plan them.
Types of additions
Most additions fall into a few types, and each comes with a different set of costs:
- Bump-out: pushes one wall out a few feet to enlarge a kitchen, bathroom or bedroom. Small footprint, but it still needs a foundation, roof and permit.
- Room addition: a new bedroom, family room, office or primary suite on the ground floor.
- Garage addition: a new or expanded attached garage.
- Room over a garage: living space built on top of an existing garage, if the structure can carry it.
- Sunroom: a lighter, window-heavy room off the back of the house.
Recent HHI estimates have covered a house extension of about 20 feet that replaced an old deck, and a new garage. Second-story additions on top of an existing house are large projects; check them against the contractor's license limit, covered below.
Permits and plans in Bismarck and Mandan
Additions are on the City of Bismarck's list of projects that require a permit, and new electrical, plumbing and HVAC work each need their own permit too. The city's Residential Building Permit Submittal Checklist (last revised December 4, 2018) spells out what a submittal needs. For an addition, that includes:
- A lot survey showing the existing house and the proposed addition, setbacks and easements, sealed and signed by a surveyor
- Floor plans showing the use of each space, doors, windows, stairs and plumbing fixtures
- Foundation plans with footing and foundation dimensions and reinforcement
- Elevations and wall sections, including footing depth below finished grade
- An engineered truss layout for floor and roof trusses
- An energy code compliance form showing the addition meets the adopted energy code
The checklist also requires an engineered design for foundation walls taller than 10 feet that support unbalanced backfill. Drafting and structural engineering are part of the addition budget, including any load-bearing wall the addition opens up. In one 2026 HHI estimate for a house extension, drafting and engineering added $2,000 to $5,000.
On timing, Bismarck's building inspections FAQ lists 7 to 10 business days of review for residential new construction and 1 business day for most other permits. Ask the Building Inspections Division at (701) 355-1465 which applies to your addition. In Mandan, call Building Inspection at (701) 667-3230 before design gets far; its requirements aren't published online in the same detail. If you're planning additions and remodeling in Mandan, we can make that call as part of the estimate.
Foundations: 48-inch frost depth in Bismarck
North Dakota ground freezes deep, and a footing sitting in soil that freezes can be pushed around as the ground freezes and thaws. That's why the City of Bismarck sets the required frost depth at 48 inches below finished grade. The footings for your addition are designed around that depth, and the plans show it in the wall sections.
What goes under the addition is one of the biggest budget decisions:
- A full basement adds the most space but means the most excavation and concrete.
- A crawl space needs less digging and still gives access to plumbing and ducts.
- A slab works for some rooms and garages and keeps the floor close to grade.
The new foundation also has to meet the existing house cleanly, with the floor levels lined up and the joint between old and new built to keep water out. The footings and foundation are poured below frost depth, and the foundation is usually the largest single line in an addition budget.
Budget drivers
We price every addition from the plans, but these are the items that move the number most.
| Driver | Why it matters | What to decide early |
|---|---|---|
| Foundation type | Basement, crawl space or slab changes excavation, concrete and time | Whether you want usable space below the addition |
| Roof tie-in | Joining a new roof to the old one is labor-heavy and has to shed snow and water | Roof shape and how it meets the existing roofline |
| Heating and cooling | Bismarck requires heat that can keep habitable rooms at 68 degrees or more | Whether the existing furnace can carry the new space |
| Windows and egress | A new bedroom needs an egress window (main-floor sleeping rooms: at least 5 sq ft of net clear opening) | Window count, sizes and placement |
| Plumbing | A bathroom or wet bar adds drain, vent and supply lines and its own permit | Whether the addition includes water at all |
| Size and shape | More corners and rooflines mean more framing and labor | A simple rectangle saves money |
| Finishes | Flooring, trim, doors and fixtures range widely in price | Matching the existing house or upgrading |
What does an addition cost per square foot?
There isn't one honest number. Every addition carries costs that don't scale with size: the permit and survey, the foundation, the roof tie-in, and the heating and electrical hookups. That's why a small bump-out often costs more per square foot than a larger room addition, and why national per-square-foot figures rarely match a local project.
Instead of a per-square-foot number, here is how one 2026 HHI planning estimate for a house extension of about 20 feet, with an old deck removed, was built up. The width and final floor area were still open, so it was priced in stages:
| Stage | What it covered | Planning figure |
|---|---|---|
| Base construction | Foundation $20,000–$25,000; general materials and labor $12,000; roof $7,500; drywall $5,000–$7,000 | $44,500–$51,500 |
| Plus drafting and engineering | Adds $2,000–$5,000; permit fee at the city's actual cost | $46,500–$56,500 + permit fee |
| Plus electrical and plumbing | Adds $20,000–$30,000 when those trades are included | $66,500–$86,500 + permit fee |
Those are planning figures for one house, not a rate for yours. Every total we take on stays within the $100,000 per-project limit of our license. The quickest way to a reliable number is a site visit, a rough sketch of the rooms you want and a written estimate.
Check the contractor's license class against your project size
In North Dakota, a contractor needs a state license for any job over $4,000, and the license class caps how big a single job can be. According to the North Dakota Secretary of State:
- Class A: over $500,000 per job
- Class B: up to $500,000 per job
- Class C: up to $300,000 per job
- Class D: up to $100,000 per job
Licenses must be renewed by March 1 each year, and you can check whether a contractor's license is in good standing through the state's FirstStop search. Before you sign, compare the license class with the contract price. HHI is licensed as Class D, so we take on additions where the contract stays within $100,000. If your project is larger, we'll tell you at the first meeting rather than after the plans are drawn.
Timeline and seasons
An addition moves through design and plans, the permit, excavation and footings, the foundation, framing and roof, rough-in work and inspections, insulation and drywall, finishes, and a final inspection. An addition is measured in months rather than weeks once you count permits, foundation work and inspections, and your written estimate includes the schedule.
Season matters most at the start. Excavation and footings are simpler before the ground freezes, so it often makes sense to plan the design over winter and break ground in spring. Footings shouldn't be poured into frozen ground, so foundation work is planned before freeze-up or after the thaw. Once the addition is framed and closed in, interior work can continue through the cold months.
Paying for an addition
Most homeowners pay for an addition with a mix of savings and financing. If you want to finance part of it, you can compare personalized home improvement loan offers through Acorn Finance. Qualified applicants may see offers from $1,000 to $100,000. The lender sets your rate and repayment term. Checking initial offers uses a soft credit inquiry; moving forward may affect your credit score. To compare loans, home equity and other options, see our guide to ways to pay for an addition.
Frequently asked questions
How much does a home addition cost per square foot?
It varies too much for one number to be useful. Fixed costs like the permit, survey, foundation and roof tie-in mean small additions cost more per square foot than larger ones. In one 2026 HHI estimate for a roughly 20-foot house extension, base construction was planned at $44,500–$51,500 before drafting, engineering, electrical and plumbing. National per-square-foot figures come from other markets, so use a local written estimate for planning.
Do I need a permit for an addition in Bismarck?
Yes. Additions are on the City of Bismarck's permit-required list, and electrical, plumbing and HVAC work need separate permits. The submittal includes a sealed lot survey, floor and foundation plans, wall sections, a truss layout and an energy code compliance form. In Mandan, call Building Inspection at (701) 667-3230 for its requirements.
How deep do footings need to be in Bismarck?
The City of Bismarck's required frost depth is 48 inches below finished grade. Footings for an addition are designed to that depth so freezing soil doesn't move them, and the depth is shown in the wall sections submitted with the permit. Foundation walls taller than 10 feet that hold back soil require an engineered design.
How long does a home addition take?
Plan for design and permits first, then construction. Construction takes months rather than weeks, depending on size, foundation type and inspections, and your written estimate includes the schedule. Breaking ground before the soil freezes, or waiting for spring, keeps the foundation stage simpler; interior work can continue in winter once the addition is closed in.
Thinking about adding space? Send a sketch, dimensions and photos of where the addition would meet the house. We budget design, site and foundation work, trade bids and construction as separate stages, within our license class. Call or text Viktor at (701) 329-9659 with your town, photos and what you want to change. Our office follows up during business hours. You can also request a free written estimate through the form below. Our employees are covered through WSI.
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