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Decks

Building your own deck is one of the top do-it-yourself jobs out there. Done right, a deck can offer years of pleasure, not to mention added value to your home. However, each year in North America, hundreds of people are injured - and some lose their lives - when decks collapse. Here are some tips to help build a better deck.

Deck blocks aren't the best approach

When to use deck blocks Deck blocks are acceptable for a single-level platform, built where the underside of the joists are no higher than 60 cm (23-1/2”) from ground level, not supporting a roof, no more than 55 m2 (592 square feet) in area, and if not attached to a building.Unfortunately, deck blocks aren't often a wise choice for building a deck. Also, in many cases, the use of deck blocks violates Building Code. Most decks are attached to another structure, and unless the soil is well-graded and not subject to frost heaves, failure to sink support to below the frost line will result in frost heaves and the risk of structural damage over time.

That's why, in most cases, decks and external stairs must be supported by concrete sunk to a depth of four feet. This can be sonotubes bearing onto a footing, or "bigfoot" foundation systems. Another means of securely supporting your deck are screw pilings: these also meet Code.

It's important to stress that 4x4 posts are not sufficient for deck loads, staircases, landings and the like. We will not approve plans for exterior platforms/stairs/decks that specify 4x4 post supports.

Section 9.17.4.1(2) of the National Building Code of Canada mandates that columns must be 14 cm x 14 cm, except for posts supporting carports (as allowed by 9.35.4.2.) This means 6x6 wood (nominal 5 1/2" on each side), not 4x4 construction.

Supporting members  must be securely attached to the footing supports. The most common means is purpose-built metal bracing designed to be set into concrete when its poured.

This deck collapsed due to a poor connection at the house. Image courtesy of Structuretech1.com.

Bolt it to the building

The connection between the deck and the structure it services is absolutely critical.

Failure of this attachment can lead to collapse, and has been linked to a number of injuries and deaths in North America.

A typical deck connection - image courtesy Regional Municipality of Halifax.

Many residential decks are constructed by first installing a section of lumber against the house, called a "ledger board," then attaching joists to the ledger board, usually with joist hangers. It is absolutely vital that  the ledger board is securely fastened to the home's rim joist or supporting beam.

The best practice is to ensure that the ledger board is fastened by long threaded bolts, held in place with washers on both sides, and a securely-tightened nut.

There are purpose-built products that also serve this function. (Alternative: lag bolts of sufficient length, staggered spacing of 45 cm (17 1/2")).

Support the load

To handle the expected loads for people, as well as snow, here's a guide to help select joists for your deck.  Joists can either be supported on a beam, or tied to it using joist hangers. 

Joist Span and Spacing Chart
S.P.F. No 1&2 Joists with Solid Bridging at ½ Span
Joist Size Joist Spacing
  12” 16” 24”
2x4 6’ - 6” 5’ - 11” 5’ - 2”
2x6 10’ - 3” 9’ - 4” 8’ - 2
2x8 12’ - 6” 11’ - 8 10’ - 8”
2x10 14’ - 6” 13’ - 8 12’ - 10
2x12 16’ - 5” 15’ - 5” 14’ - 6”

Reading the above, if you're planning on trying to span 12' without a mid-range support, you would need 2x8 joists set at 12" on centre; or 2x10 joists at 24" on centre.

The usual construction for a deck involves joists running from the house to an outside supporting beam. The table below gives a general guide as to how to build the beam so it can support the anticipated loads of a deck. Beams should be nailed together securely. Butt joints should, if at all possible, be made over post supports. Splices can take place within 1/4 of the total span from mid-range supports. For more details, see our beam-building guide, here.

Beam calculator
Beam size Supported joist length
8’ 10’ 12’ 14’ 16’
Maximum distance between post supports
Three-ply 2x8 10’ - 0” 9’ - 4” 8’ - 7” 7’ - 11” 7’ - 5
Four-ply 2x8 11’ - 0” 10’ - 3” 9’ - 8” 9’ - 2” 8’ - 7”
Three ply 2x10 12’ - 10” 11’ - 6” 10’ - 6” 9’ - 8” 9’ - 1”
Four ply 2x10 14’ - 1” 13’ - 1” 12’ - 1” 11’ - 2” 10’ - 6”
Three-ply 2x12 14-11” 13’ - 4” 12’ - 2” 11”3” 10’ - 6”
Four-ply 2x12 17’ - 2” 15’ - 4” 14’ - 0” 13’ - 0” 12’ - 2”

Once the joist span is known, the size of the outside supporting beam can be determined, by following the column down, and reading across to gain a sense of how frequent the supports must be, and how large the carrying beam must be. Questions? Give us a call: we'll help you out.

Guards (railings)

Building Code requires guards - commonly called railings - to be installed on decks where the platform is 60 cm above the ground, or when the adjacent ground slopes at a 1:2 grade away from the deck area. These guards must be securely fastened, and set at a height of no less than 90 cm (35 1/2") from the deck surface. Additionally, National Building Code requires vertical elements (balusters) separated by no more than 10 cm, and designed so as not to aid climbing: this is to minimize the risk of small children climbing the element and then falling.