Code Requirements for Basements
The State of Minnesota has updated the building code effective January 24, 2015. We are in the process of reviewing our website to make sure everything is up to code, but you should always review the State of Minnesota Building Code before beginning any project.
- General Information
- General Framing Information
- Fireblocking & Draftstopping
- Drilling & Notching of Framing
- Smoke Alarms & CO Detectors
- Combustion Air for Appliances
- Gypsum Wallboard (Drywall)
- Electrical Installations
- Plumbing Installations
- Heating Installations
- Ceiling heights in basements should be a minimum of 7 feet.
- Bathrooms must be provided with ventilation via a window of not less than 3 square feet or a mechanical exhaust fan with a minimum rating of 50 cfm. Rigid metal duct creates much less resistance to air flow and will improve the efficiency of your bath fan.
- Toilets must be installed in a space at least 30 inches wide and at least 24 inches of clear space must be provided in front of the toilet.
- Showers should have a clear space within the stall of at least 30 inches.
- Fireplaces and stoves may be installed in basements but must be installed in strict accordance with the manufacturers written instructions.
- Bedrooms must be at least 70 square feet in area.
- Nail plates should be installed wherever nails or screws may come in contact with electrical wiring or plumbing or gas piping.
- Electrical wiring installations are subject to inspection by the State Board of Electricity. Call 612-798-1877 for information on permits and inspections.
An egress window is required in every bedroom and in unfinished basements when habitable space is first added or habitable space is expanded. If an egress window is installed in a basement bedroom, an additional egress window is not required in the balance of the basement unless there are additional bedrooms.
Non-bearing wood framed walls may be 2 by 4 studs at 16 or 24 inches on center. Walls must have a bottom plate and at least a single top plate. Plates in contact with concrete floors must be treated wood, redwood, or cedar. For stud size and spacing for bearing walls, contact the Inspections Department. Wood used for framing soffits may be 2 by 2 material.
Headers in non-bearing walls may consist of a 2 by 4 laid flat for openings up to 8 feet wide. No cripples or blocking is required above the header provided the distance from the header to the floor joist above is not more than 24 inches. For headers in bearing walls, contact the Inspections Department.
Do not remove any existing partitions unless you have determined that they are not load bearing partitions. If any portion of a load bearing partition is removed, a header or beam must be installed to transfer the load to a footing.
Wood Furring Strips
Treated wood furring strips not less than 1 by 2 inch may be attached directly to the interior of exterior masonry or concrete walls below grade or untreated strips may be used if an approved vapor retarder is installed between the wall and the furring strips.
Wood Veneer Paneling
Wood veneer paneling must be placed on wood framing spaced not more than 16 inches on center. Wood veneer paneling less than ¼ inch nominal thickness must have not less than a 3/8 inch gypsum board backer.
Fireblocking (PDF) is required in a number of locations to impede the spread of smoke, hot gases, and flames through the framework in the event of a fire.
Draftstopping is required whenever dropped ceilings or open web joists are used and a concealed space is created that exceeds 1000 square feet in area.
Drilling & Notching of Framing Members
- Drilling and notching of open web trusses or laminated veneer lumber (LVL) beams is not permitted without an approved design from the truss manufacturer or a structural engineer.
- Drilling and notching of I-joists is permitted in accordance with the manufacturers written installation instructions. You should obtain a copy of these instructions before starting any work.
- Drilling and notching of standard wood members is subject to the following:
- Notches in joists, rafters, and beams may not exceed one-sixth of the depth of the member, may not be longer than one-third of the depth of the member and may not be located in the middle third of the span.
- Notches at the ends of a joist, rafter, or beam may not exceed one-fourth the depth of the member.
- The diameter of holes bored or cut into joists, rafters, and beams may not exceed one-third the actual depth of the member. Holes may not be closer than 2 inches to the top or bottom of the member or any other hole located in the member. Where the member is also notched, the hole may be no closer than 2 inches to the notch.
- When piping or ductwork is placed in a wall necessitating the cutting of the top plate by more than 50% of its width, a galvanized metal tie of at least 16 gage and 1 ½ inches wide must be fastened to each plate across and to each side of the opening with not less than six 16d nails.
- Exterior or bearing studs may be cut or notched to a depth not exceeding 25% of their width.
- Interior nonbearing studs may be notched to a depth not to exceed 40% of a single stud width.
- Exterior or bearing studs may be bored or drilled provided that the diameter of the resulting hole is no greater than 40% of the stud width, the edge of the hole is no closer than 5/8 inch to the edge of the stud, and the hole is not located in the same section as a cut or notch.
- Exterior or bearing studs may be bored or drilled provided that the diameter of the resulting hole is not greater than 60% of the stud width and provided that the studs are doubled and not more than two successive studs are bored, the edge of the hole is no closer than 5/8 inch to the edge of the stud, and the hole is not located in the same section as a cut or notch.
- Interior nonbearing studs may be bored or drilled provided that the diameter of the resulting hole is no greater than 60% of the stud width, the edge of the hole is no closer than 5/8 inch to the edge of the stud, and the hole is not located in the same section as a cut or notch.
- Approved stud shoes may be used when installed in accordance with the manufacturer's recommendations.
There are essentially two ways that exterior basement foundation walls can be insulated: with the use of foam plastics and various types of furring strips or with a conventional wood stud partition and fiberglass batts. Whenever foam plastics are used, they must be covered with a layer of ½ -inch gypsum board unless the foam plastic is approved for use without the covering.
Foundations should be insulated to an R-10. A vapor retarder is required on both the warm side of the insulation and against the foundation wall. Rim joist areas must also be insulated to R-10. To avoid problems with condensation and mold in the rim joist area, it is recommended that you use one of the foil faced foam insulations and seal the foam into place between the joists. If the ceiling will not be finished and the foam in the joist space will be left exposed, it must be covered with ½ -inch gypsum board unless the foam plastic is approved for use without the covering.
Smoke alarms are required in every bedroom and on each floor of the dwelling, including the basement. Alarms must be installed in accordance with the manufacturers' written instructions.
- Where framing is exposed, alarms must be hard wired with a battery backup and must be interconnected with other hardwired alarms. If the basement ceiling is exposed to allow wiring to be connected to main floor smoke alarms, then those alarms are required to be hardwired with battery backup.
- When framing is not exposed or it is not feasible to hardwire a smoke alarm, battery powered detectors may be used.
Read more on smoke alarms.
CO detectors must be located within 10 feet of all bedroom doors. The rules for hardwired or battery operated CO detectors are the same as for smoke detectors.
Combustion Air for Furnaces & Water Heaters
An often-overlooked problem with basement finishing is the confinement of fuel burning appliances and the resultant poor performance due to a lack of sufficient oxygen. If you are enclosing the space housing your furnace and/or water heater, you may need to provide additional combustion air by installing an exterior combustion air duct or providing openings in the enclosing walls or doors. If you have any questions regarding the issue of combustion air, please contact the Inspections Department.
All electrical work is subject to permits and inspections. The State Board of Electricity administers the Electrical Code. The local contact is Doug Torvund, 612-866-5895.
Mechanical permits are required for the installation or alteration of mechanical systems. Because basements tend to be cool when weather does not cause furnaces to run often, you may wish to consider the installation of electric baseboard heaters to supplement your existing heating system. They provide a safe means to raise the temperature in occupied rooms and are inexpensive to install and operate.