decking

Building a Deck

Building permits are required for decks with the following exceptions:

  • Freestanding decks (decks not connected to a structure), regardless of size, will not require permits if they are not more than 30 inches above adjacent grade. Freestanding decks and decks that are not structurally attached to the dwelling do not require footings that extend below the frost depth.
  • Building permits are also not required for patio slabs on grade.

Applying for a permit

Submit an application and two sets of your building plans (elevation, site plan and floor plan). Building permits for decks will typically be processed within 5 business days of receiving a complete set of plans.

Inspections

The Inspections Department will typically make two or three inspections of your deck during the course of construction. It is your responsibility to call for an inspection 1-2 days in advance of the time you need an inspection.

Inspection 1: Post Footings

At the time of the inspection, the holes should be dug and all loose material should be removed but no concrete should be poured. The inspector will check:

  • the depth of the footing and its width at the base
  • the location of the footings for compliance with the zoning ordinance

Inspection 2 & 3: Framing and Final

These can be combined into one inspection if the underside of the deck is fully visible, as would be the case with a bi-level home. If it's not possible to view the deck from below, the framing inspection should be made prior to decking being applied. The inspector will check:

  • the size and spacing of joists, beams and columns
  • the attachment to the dwelling including flashing, the type of fasteners and lumber being used
  • setbacks

When the final inspection is made, the inspector will check:

  • the type of decking used
  • railings, stairs, and landings

Code requirements and important information

Location & Setbacks

Decks are permitted:

  • as an addition to a dwelling in a side or rear yard; or
  • as a freestanding structure.

Decks must be at least 3 feet from a neighbor's property line and should be 10 feet from a rear property line.

Setbacks are routinely checked as a part of the plan review and again at the time of the footing inspection. Questions regarding setbacks or lot coverage should be directed to the Zoning Administrator at 952-548-6342.

Fasteners

  • Nails and other hardware must be hot-dipped zinc-coated (galvanized), stainless steel or equally well-protected material. Screws should be either hot-dipped galvanized or electroplated with a polymer coating. Some fasteners may stain some species of wood. If this is a concern, you may wish to check with the fastener supplier for guidance.
  • Place nails no closer to the edge than about half the board thickness. When nailing closer to the edge, pre-drill holes.
  • Use 12d nails on nominal two-inch decking. 10d nails are recommended for 5/4" decking.
  • With lag screws, use a flat washer under the head. Use washers under the nut and head of machine bolts and just under the nut of carriage bolts.

Lumber

All wood used in deck construction must be pressure treated lumber or wood that is naturally resistant to decay such as redwood or cedar.

Lumber is treated to varying degrees. Numbers such as 0.25, 0.40, and 0.60 pounds per cubic foot (pcf) represent the amount of preservative retained in the wood. For example, 0.25 indicates that 1/4 pound of preservative is in every cubic foot of wood fiber in the assay zone.

Wood used above ground should be treated to 0.25 pcf, for ground contact to 0.40 pcf, and to 0.60 pcf for wood foundations and embedment in the ground. Because the new preservative treatments are very corrosive, verify that any metal connectors used in the construction of your deck are approved by the manufacturer for use with treated wood.

Treated wood may have a high moisture content when delivered to the worksite and will undergo some shrinkage as the material dries. You should plan for this shrinkage when laying out decking or using long spans.

After construction, allow the wood to dry before applying paint, stain or water repellant. You can check its readiness by seeing how fast the wood absorbs a few drops of water, or by applying the coating to a small piece to see if it absorbs properly. If you don't have time to wait, use wood marked KDAT (kiln-dried after treatment).

Decking Materials

Materials commonly used for decking include standard dimension lumber (either 2x4 or 2x6), radius-edged decking, or a manufactured decking product.

Dimension lumber that is 2X6 in size is the only lumber product that can be used for decking on joist spacing of 24 inches. While lumber wider than 2x6 may be used, you may experience problems with undesirable cupping and for this reason it is recommended that decking be limited to 2x6 or smaller lumber.

Radius-edged Patio Decking has been specifically developed for outdoor decks. Patio decking is intended to be used flat-wise in load-bearing applications where spans do not exceed 16" on center. Its thin profile and oversized eased edges make it suitable where a stock thinner than 2" is desirable.

Manufactured decking products are available in a variety of designs, colors, and materials. Deck builders should be aware that there are some decking products on the market that are not approved and will not pass inspection. The decking supplier should be able to provide you with a listing for the deck material that indicates it has been approved by a nationally recognized testing agency. If they cannot provide a listing, you should contact the Inspection Division for approval prior to purchase. The Inspections Department maintains a list of decking materials that have been approved for use in Minnesota that is available upon request.

Footings

Prior to excavating for any footings, be sure to call Gopher State One Call at 1-800-252-1166 for utility locations.Deck footing diagram

Deck footings should be sized according to the following table. Footings must extend at least 42 inches below grade except for decks that are not connected to a dwelling.

Deck Footing Sizes
A B C
Diameter of Footing Base in Inches Area Supported with Concrete Footer Only 1,2,3 (In Sq Ft) Area Supported with Solid Concrete Pier 1,3,4 (In Sq Ft)
6 8 6
8 14 11
9 18 13
10 22 16
11 26 20
12 31 23
13 37 28
14 43 34
15 49 40
16 56 47
17 63 54
18 71 61

1. Based on assumed soil bearing capacity of 2000 lbs per square foot.
2. Concrete footers to be 6 inches thick minimum.
3. All dimensions are approximate.
4. For solid concrete piers greater than 12 inches in diameter, the footing area is obtained by belling the bottom of the pier.

Required footing sizes are determined by calculating the area of the deck supported by each footing, dividing the area by the appropriate value in column B or C, and locating the appropriate footing size in column A. Loads between columns, walls, and beams shall be assumed to be equally shared between the supporting elements. The entire load for cantilevers should not be overlooked.

Post footings supporting a 4x4 column must be not less than 6-inch diameter. Post footings supporting columns larger than 4x4 must be not less than 8-inch diameter. The bottom of post footings may be "belled" to achieve the desired minimum bearing area. The base of the footing should be at least 42 inches from finished grade.

The use of a fiberboard tube will allow you to elevate the top of the footing 1-2 inches above finished grade to provide protection of the wood post from lawn mowers and trimmers. The tube will also reduce the potential for frost to "heave" the post footing. You may wish to provide a slight crown to the top of your footing to promote good drainage.

A concrete pier can be substituted with a treated post extended down to the top of a concrete footing pad. The post must be 60% p.c.a. or equal.

Ledger Board

The ledger board attaches to the house frame or foundation. Installing the ledger board first, establishes the height and width that makes it easy for laying out the rest of the deck. For a standard installation the top of the ledger board should be attached about 2-1/4 inches below the bottom of the doorway threshold. This provides a 3/4-inch space between the top of 2x6 decking and the bottom of the threshold. This deck surface will lie 1-2 inches below the flooring of the house. Care should be exercised when securing the ledger board to be sure it is level. Install metal flashing at top, and caulk sides and bottom.

Attaching Ledger Board

Thru bolts or lag bolts must be used to secure the ledger board to the dwelling. The ledger board should be secured as follows:

  • For joist spans less than 10 feet — 3/8" or 1/2" at 24" o.c.
  • For joist spans of 10-15 feet — 3/8" or 1/2" at 16" o.c.
  • For joist spans of 15-20 feet — 3/8" or 1/2" at 12" o.c.

The bolts should be long enough to penetrate the house framing at least 1 1/2 inches.

On a fairly flat siding you can place shims between the ledger and the siding to allow water to drain. If the siding is shaped like clapboard or most vinyl siding, you can attach the ledger to shims that have been pre-cut to fit over the siding. Another option is to cut away some of the siding to expose the flat sheathing surface.

ledger board 1ledger board 2

Beams and Posts

Minimum Beam Sizes
Length of Span (Ft) Spacing Between Posts (Ft)
   4 5 6 7 8 9 10
6 (2)
2X8s
(2)
2X8s
(2)
2X8s
(2)
2X10s
(2)
2X10s
(2)
2X10s
(2)
2X12s
7 (2)
2X10s
(2)
2X10s
(2)
2X10s
(2)
2X10s
(2)
2X10s
(2)
2X12s
(2)
2X12s
8 (2)
2X10s
(2)
2X10s
(2)
2X10s
(2)
2X12s
(2)
2X12s
(2)
2X12s
(3)
2X12s
9 (2)
2X10s
(2)
2X10s
(2)
2X12s
(2)
2X12s
(2)
2X12s
(3)
2X12s
X
10 (2)
2X10s
(2)
2X12s
(2)
2X12s
(3)
2X12s
(3)
2X12s
X X
11 (2)
2X12s
(2)
2X12s
(3)
2X12s
(3)
2X12s
X X X
12 (2)
2X12s
(3)
2X12s
(3)
2X12s
(3)
2X12s
X X X
X = Beams larger than 2x12 recommended

beam diagramConstruct the beam using two or more 2 inch nominal pieces of lumber in accordance with the above table. The beam should be nailed together using 16d nails at 16 inches o.c. along each edge of the beam. A spacer may be used to fir the beam to a 3 1/2 -inch width. Beams should be installed with any arch or crown facing up.

Minimum Post Sizes
Height (Ft) Load Area (sq. ft) = beam spacing X post spacing
  48 72 96 120 144
up to 6 4x4 4x4 6x6 6x6 6x6
up to 8 6x6 6x6 6x6 6x6 6x6
Vertical loads figured as concentric along axis.
No Lateral loads considered.
6X6 posts require a minimum 8-inch diameter footing.

Deck PostDeck Posts

Ribbon JoistsRibbon Joists

Floor Joists

Southern Pine #2
(Frequently used for treated wood)
  12" o.c. 16" o.c. 19.2" o.c. 24" o.c.
2x6 10-9 9-9 9-2 8-6
2x8 14-2 12-10 12-1 11-0
2x10 18-0 16-1 14-8 13-1
2x12 21-9 18-10 17-2 15-5
Redwood
   12" o.c. 16" o.c. 19.2" o.c. 24" o.c.
2x6 10-3 9-4 8-9 8-2
2x8 13-6 12-3 11-6 10-3
2x10 17-3 15-4 14-0 12-7
2x12 20-8 17-9 16-3 14-6
Cedar
   12" o.c. 16" o.c. 19.2" o.c. 24" o.c.
2x6 10-3 9-4 8-9 8-2
2x8 13-6 12-3 11-6 10-3
2x10 17-3 15-4 14-0 12-7
2x12 20-8 17-9 16-3 14-6
Cantilevers for floor joist will be limited to the following:
2X8 @ 16" or 24" o.c. 8 inches
2X10 @ 16" o.c. 20 inches
2X10 @ 12" o.c. 26 inches
2X12 @ 16" o.c. 29 inches
2X12 @ 12" o.c. 36 inches
Note: The back span to cantilever ratio must be not less than 3:1. Solid blocking is required at the bearing points for cantilevers in excess of 12 inches. A full depth rim joist is required at the cantilevered end of the joists.

Deck joists

Unless joists bear on a beam or ledger strip, they must be supported by joist hangers. Joist hangers must be installed in accordance with the manufacturers recommendations. Joists should be installed with the crown side up.

For high decks additional lateral bracing is required and is usually installed in the form of a 2x4 or 2x6 that is nailed or screwed diagonally across the bottom of the deck.

Decking

Maximum Spans For Spaced Deck Boards
5/4 and 2X4 16 inches
2X6 24 inches

Deck board crownDecking should be installed so the crown of the board is up. If decking has a slight bend to it, you may be able to straighten it as it is nailed in place.

In addition to treated wood, cedar, and redwood, there are many new decking products on the market. Not all of these products have been tested and approved. Check with the Inspections Department before purchasing any man-made decking products.

Railings

Deck railing diagramGuardrails are required for decks 30" or more above grade. The height of the rail must be a minimum of 36". Open guardrails must have intermediate rails or ornamental pattern that a 4" sphere cannot pass through. Guardrails must continue down stairs where the stair is more than 30 inches above grade.

Other Helpful Resources

Contacts

  • Administrative Assistant

    952-548-6320
  • For information specific to setbacks:
    City Planner

    952-548-6342