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Residential Decks

drawing of two people building a deck with stairs

Thief River Falls 
Building Department
405 Third Street East, P.O. Box 528, Thief River Falls, MN 56701
Phone: (218) 681-2500 Fax: (218) 681-6223

Residential Decks
1 & 2 Family Dwellings and Townhomes
Based on the 2003 Minnesota State Building Code

MR = Minnesota State Building Code extracted from 2003 Minnesota Rules

IRC = International Residential Code

NEC = National Electrical Code

Residential Decks 

Building Permit Requirements: Building permits are required for the construction of all decks that are attached to the home. Building permits are also required for freestanding decks that are elevated 30” or more above grade with supporting beams, joists, or posts. Deck construction shall meet the requirements of the 2003 Minnesota State Building Code which adopts and amends the 2000 International Residential Code.

Zoning Requirements: Decks are also required to meet the land use and setback requirements of the zoning code. Zoning questions should be directed to the Thief River Falls Building Department at 218-681-2500.

Permit Fees: The building permit fees are based on the size of the deck and are designed to cover the cost of the plan review and field inspections that will be performed during construction. An estimate of the permit costs (based on the size of the deck) may be obtained by calling the Building  Department. The cost of the building permit includes the permit fee, plan review fee, zoning fee and Minnesota surcharge.

Plan Review & Inspections: The plan review is done by the plans examiner in order to spot potential problems or pitfalls that may arise prior to construction. Typically the plan review for a residential deck will be done at the counter during normal work hours. Construction inspections will be done during the project to ensure code compliance and that the materials used are installed correctly. The plan review and inspections are not designed to be a guarantee of the work but they are done to provide a reasonable degree of review and observation so the project will be successful, safe and long-lasting.

Submittals for permit: The following information is necessary for the Building Department to do a proper plan review and to help the project go as smoothly as possible. Note: Sample plans provided with this information are intended as a guide only.

  • A completed building permit application form.
  • Two copies of the site plan. The site plan should indicate the existing structure, proposed deck location and lot dimensions (see sample site plan on exhibit 4). A copy of the existing site plan may be obtained from the Building Department if one is on file.
  • Two copies of the construction plans showing the proposed design and materials. Plans shall be drawn to scale and indicate the following information:

A. A floor plan including the following: (see sample plan exhibit 5)

  1. Proposed deck size with dimensions. (see sample plan exhibit 5)
  2. Size and spacing of floor joists. (see exhibit 9)
  3. Size and type of decking material.
  4. Size, location and spacing of posts including post connection to footing (see sample plan exhibit 5)
  5. Size of beams (see exhibit 10). Also indicate post/beam connection (see beam connection details exhibit 6)
  6. Species and grade of lumber to be used and proper connectors to be used.

B. Elevations indicating the following: (see sample elevation exhibit 6)

  1. Height of structure from established grade.
  2. Diameter and depth of footings.
  3. Guard height and spacing of intermediates (see exhibits 6 & 7)
  4. Stairway rise/run and handrail requirements (see exhibits 7 & 8)
  5. Clearance to overhead wires, if applicable. (see exhibit 6)

Land-use Requirements: Contact the Thief River Falls Building Department at 218-681-2500 for setback requirements and other zoning requirements.

Building Code Requirements:

  • Footings shall be designed and constructed below frost depth. A 60” minimum ground cover is required from bottom of footing to grade. (see exhibits 5 & 6) MR 1303.1600  Call Gopher One at least 2 full days before you dig at 1-800-252-1166 or send an email.
  • Decks exposed to the weather must be constructed with wood of natural resistance to decay or treated wood. This includes horizontal members such as beams, joists, ledger boards and decking; and vertical members such as posts, poles, guards, handrails and columns. Other man-made products are subject to approval by the Building Department before use. MR 1303.2000
  • Columns and posts supporting decks exposed to the weather or water splash must be supported and connected to concrete piers or metal pedestals. Columns and posts in contact with the ground or embedded in concrete must be of pressure-treated wood approved for ground contact. IRC R323.1.3
  • Decks shall be designed and constructed to support a minimum live load of 40 pounds per square foot. The dead load is assumed to be a minimum of 10 pounds per square foot for a total design load of 50 pounds per square foot. IRC R301.4 & R502.3.1(2)  Additional loads shall be considered if a spa is to be placed on the deck.
  • Ledger boards shall be bolted or lagged to the existing building framing with a minimum of two 3/8” x 5” lag screws or bolts at 16” on center. All connections between the deck and dwelling must be flashed with corrosion-resistive flashing. (see exhibit 5) IRC R502.2. Solid blocking must be provided for the attachment of the deck ledger board. IRC R602.3
  • Fasteners and hangers to be hot-dipped galvanized steel, stainless steel or copper. Due to new treating processes additional requirements may apply. (check with lumber supplier)
  • Joists shall not overhang beams by more that 2’-0”, nor should beams overhang posts by more than 1’-0” at each end. IRC 502.2
  • Floor joists and stair stringers spaced at 24” inches on center require a minimum 2” nominal decking. For floor joists and stair stringers spaced at 16” inches on center, 1” decking or 5/4” decking may be used. However, 16” joist spacing cannot be used if 1” or 5/4” decking is placed diagonally. IRC R502.2
  • All decks, balconies or porches which are more than 30” above grade or a floor below must be protected by a guard a minimum of 36” above the finished deck surface. Guards and stair railings shall have horizontal, vertical, diagonal or other ornamental intermediate rails through which a sphere 4” in diameter cannot pass through. (see exhibits 6 & 7) IRC R316
  • The electrical code requires overhead power lines to be located a minimum of 10’-0” above decks and platforms. Existing lines may need to be raised if a new deck is to be installed beneath them. Contact Thief River Falls Electrical Department at 218-681-5816 with any questions regarding relocation of power lines. (see exhibit 6) NEC
  • Decks built to support a future porch should be constructed so that all potential imposed loads are taken into consideration; full porch plans should be submitted for future reference.
  • If the deck will encroach on public utilities call the following for regulations on clear space requirements.

Water - City of TRF
(218) 681-3809

Wastewater - City of TRF
(218) 681-3809

Electric - City of TRF
(218) 681-5816

Gas - Minnesota Energy Resources
(218) 681-3226

Required Inspections:

Every effort is made to perform all inspections the next business day following the request. Inspection requests must be received prior to 4:30 pm if the request is for next day service. Call Thief River Falls Building  Department at 218-681-2500 to schedule an inspection. Please have your permit number and address available when you call. Inspector work schedules fill up fast at certain times of the year, so if you can call more than a day in advance, you may avoid any potential delays in the progress of your project.

  • Footings: To be made after the holes are dug to required depth and size, but prior to pouring of the concrete!!
  • Final: To be made upon completion of the deck and finish grading.
  • Other Inspections: In addition to the above inspections, the inspector may require other inspections to ensure compliance with the code.

General Notes

The approved set of plans, survey & inspection card shall be kept on the job site until the final inspection has been made and approved.

Any contractor used must be licensed by the State of Minnesota, or have a Certificate of Exemption from the State of Minnesota.

Call Gopher One at least 2 full days before you dig at (1-800) 252-1166 or send an email.

Exhibit 4 Sample Site Plan

Exhibit 5 Ledger Connection Detail, Footing Examples, Floor Plan

Exhibit 6 Post Beam Connection, Side Elevation

Exhibit 7 Stair and Landing Requirements

Exhibit 8 Acceptable Handrail Examples

Exhibit 9 Joist Span Table

Exhibit 10 Beam Size Table