Deck Materials Guide for Canada: Boards, Joists, Screws, and Footings

Start with the deck, not the shopping list

A deck materials list only makes sense once the deck itself is defined. Size, height, board direction, joist spacing, stair location, and railing plan all change what you need to buy. Two decks with the same surface area can have quite different lists if one runs boards diagonally, needs a picture frame border, or sits high enough to need more substantial railing and stair work.

This guide walks through how the counts are built, step by step, so you can check a calculator result instead of trusting it blindly. It uses metric measurements first, with imperial in parentheses where natural, which matches how many Canadian plans and lumber labels present information. Lumber in Canada is still commonly sold using nominal imperial names, such as a 2 by 6, even when the tape measure work for layout is done in millimetres and metres. Keeping both systems visible, and labelled, prevents the most common ordering mix ups.

This is an estimating guide, not a building code substitute and not structural advice for your specific property. Deck loads, spans, footing depth, railing requirements, and permit rules vary by municipality and by design. Use the math here to build an accurate list, then confirm the structure itself with your local building department, your plans, and qualified help where your project requires it.

The pieces of a deck, in order from the ground up

Thinking from the ground up keeps a list complete. At the bottom are footings, usually concrete in holes or in tube forms, sized and placed to carry posts. Above them sit posts, beams, and joists, which together form the frame. On top of the frame sit the deck boards you walk on. Around the edges and at any height change come fascia, railing, and stairs. Fasteners hold the whole system together: structural screws or bolts for the frame, and deck screws or hidden fasteners for the surface boards.

If you list materials in that same order, you are less likely to forget the unglamorous items that stop a build mid weekend: joist hangers, post bases, beam hardware, ledger flashing where a deck attaches to a house, end cut treatment for treated lumber where the product instructions call for it, and the extra boards you need for cutting waste and for the one board that arrives with a defect you do not want in the middle of the floor.

Board direction decides the first calculation

Deck boards have a length direction and a coverage direction, and confusing the two is the fastest way to order the wrong count. If boards run along the long side of a rectangular deck, each board covers a strip across the short side. The number of boards is decided by the short side dimension, the board width, and the gap between boards. The length of each board is decided by the long side, plus any overhang or border detail in your design.

If you add a picture frame border, diagonal inlay, or a change of direction in the middle, split the deck into zones on paper and calculate each zone separately. A calculator that assumes one simple direction will undercount a patterned deck, and the shortfall only appears when the pattern is half laid.

Joist spacing and why it matters twice

Joists support the boards, and their spacing affects both the frame count and the fastener count. Closer spacing generally means more joists, more hangers, and more screw crossings per board. Wider spacing means fewer joists, but it must still suit the board product and the span in your approved design. Board manufacturers publish spacing guidance for their products, and diagonal layouts often need closer spacing than straight layouts because each board crosses joists at an angle and the effective span feels different underfoot.

For estimating, joist spacing is usually described as centres, written as on centre spacing. A spacing of 400 mm on centre (about 16 inches) means the middle of one joist to the middle of the next is 400 mm. The count is not simply deck length divided by spacing. You need to account for the joist at the starting edge as well, which is why the worked example below adds one after dividing.

Worked example

This example builds a full count for one straightforward rectangular deck. Every assumption is stated so you can substitute your own dimensions.

Assumptions: the deck is 4.8 m long by 3.6 m wide (about 16 feet by 12 feet in round imperial terms, though the metric figures govern the math here). The finished deck boards are 140 mm wide. The gap between boards is 5 mm. Boards run parallel to the 4.8 m side, so each board is 4.8 m long before any trimming, and boards are laid across the 3.6 m width. Joists run across the 3.6 m direction and are spaced at 400 mm centres along the 4.8 m length. Each board is fixed with 2 screws at every joist crossing. The deck has 6 posts, each on its own footing, to illustrate the footing link. No stairs, border pattern, or diagonal layout are included in this core example.

Step 1: Effective coverage per board

Add board width and gap: 140 mm plus 5 mm equals 145 mm. Convert to metres: 145 mm divided by 1,000 equals 0.145 m. Each board, once laid, covers 0.145 m of the deck width, counting its share of the gap.

This is the step most hand estimates miss. Dividing by the bare board width of 140 mm overstates coverage and understates the count, because the gaps, small as they look, add up across more than twenty boards.

Step 2: Number of deck boards

Divide the width to be covered by coverage per board: 3.6 divided by 0.145 equals 24.83. Round up to the next whole board: 25 boards.

Check the coverage: 25 boards multiplied by 0.145 m equals 3.625 m, which covers the 3.6 m width with a small remainder that is handled in layout by adjusting the final gap or trimming the last board, according to your design and the board instructions. Ordering 24 boards would cover only 24 multiplied by 0.145, which equals 3.48 m, leaving a visible shortfall. The rounding step is not waste. It is the difference between a finished floor and a gap at the edge.

Total board length before waste: 25 boards multiplied by 4.8 m equals 120 m of deck board. If you buy boards in fixed lengths, map that total onto the available lengths with your supplier, allowing for cuts, defects, and end trimming. Add a waste and selection allowance on top. A simple straight deck with good stock might use a modest allowance, while a deck with many cuts, stairs, or a border will need more. State the allowance you chose in your list so the count can be audited later.

Step 3: Number of joists

Divide the deck length by joist spacing in metres. Spacing is 400 mm, which is 0.4 m. So 4.8 divided by 0.4 equals 12 spaces.

Add one joist for the starting edge: 12 plus 1 equals 13 joists.

Each joist spans the 3.6 m width in this layout, before any cantilever or beam detail in a specific design. The joist count of 13 is an estimating count for this stated layout. A real frame also needs rim boards, blocking, beams, posts, and a ledger or independent support detail, all of which belong on the full list even though they are not part of this board and screw calculation.

Step 4: Screws for the deck surface

Count crossings per board. Each board crosses every joist once, so crossings per board equals the joist count: 13.

Screws per board: 13 crossings multiplied by 2 screws per crossing equals 26 screws per board.

Total surface screws: 26 multiplied by 25 boards equals 650 screws.

Add a small extra quantity for dropped, damaged, or misdriven screws and for stair treads or a border if your design adds them later. If you use hidden fasteners instead of face screws, the count logic changes completely, because clips are typically counted per crossing in a different pack format. Do not convert a face screw count into a clip count one for one. Recalculate using the fastener system instructions for the board you selected.

Note what this screw total does not include. It does not include structural fasteners for the ledger, beams, post bases, joist hangers, or railing. Those are separate line items with their own specified products. Mixing surface screws into structural connections is not a substitution any estimator should make.

Step 5: Footings for the posts

This deck assumes 6 posts, so it needs 6 footings, one under each post, located according to the frame plan. The concrete volume for each footing depends on hole diameter and depth, which are set by local requirements and soil conditions, not by the deck surface math.

To link the two calculations, use the round hole method. As an illustration only, a hole 300 mm in diameter and 1.2 m deep has a volume of about 0.085 cubic metres, worked in full in the Mississippi Maple concrete guide. Six such holes would need 0.085 multiplied by 6, which is about 0.51 cubic metres before waste. Treat diameter and depth as values to confirm locally. Do not copy the illustration as a design for your property.

Building the full materials list

With the core counts done, expand them into a list you can actually shop from. Group the list the way the build happens, and write the quantity, the size, and the reason beside each line. A list that says only a number invites the wrong product to be substituted at the yard.

Start with footings and below ground items: concrete, tube forms if used, post bases, and any gravel for the base of holes where your design calls for it. Then list the frame: posts, beams, joists, rim boards, ledger board if the deck attaches to the house, flashing, hangers, and structural fasteners specified for each connection. Then list the surface: deck boards with the count from Step 2 plus your stated allowance, fascia boards, and surface fasteners from Step 4. Then list railing and stairs as their own sections, because both contain many small parts that vanish from a one line estimate: posts, rails, balusters or other infill, stair stringers or the lumber to cut them, treads, and the hardware for each.

Finish with consumables and protection: saw blades suited to the board material, drill and driver bits, spacers for consistent gaps, end treatment or stain if your product plan includes it at build time, and safety equipment. In Canada, also think about timing. Spring demand for treated lumber and composite boards can be strong, and specific lengths sell out first. A list finished early lets you confirm length availability before you commit to a board length strategy that depends on one size.

Lumber sizes and the nominal size trap

A board sold as a 2 by 6 is not actually 2 inches by 6 inches once milled and dried. The name is nominal. The deck board width used in the worked example, 140 mm, is presented as the actual finished width for the calculation, which is the only width that matters for coverage. Whenever you calculate, use actual dimensions, not shelf names. If a product lists an actual width of 140 mm, use 140 mm. If a different product is actually 137 mm or 142 mm wide, redo Step 1 and Step 2 with that figure. A difference of a few millimetres per board becomes a full board difference across a wide deck.

The same care applies to length. Confirm whether a stated board length is exact or approximate, how much you will trim from ends for a clean finish, and whether butt joints are part of your design. A deck that needs long, unjointed boards in every row is a different order from a deck where joints are planned and staggered over joists.

Waste, defects, and spares

Every deck list needs an explicit allowance, written as a percentage or as extra boards, with a reason. Cuts around posts, trimming to a straight final edge, boards rejected for a knot or warp in a prominent spot, and simple mistakes all consume material. Keep one or two extra matching boards after the build if storage allows. Matching a profile and colour years later can be difficult, and a stored spare is the simplest way to handle a single damaged board.

For screws and hardware, extras are cheap insurance compared with a mid build trip. For concrete, extras are heavier to handle, so balance the allowance against delivery or bag handling. The right allowance is the one you chose deliberately for your layout, not a number copied from a different deck.

Canadian considerations that change the list

Frost movement is a central design fact in most of Canada. Footing depth, and in some places footing type, responds to local frost depth and soil. Pergola style surface piers that might suit a mild climate are not automatically suitable where the ground freezes deeply. Your municipal building department and, where required, your permit drawings govern this part of the build.

Snow load and use also matter. A deck that will hold a large hot tub, a heavy outdoor kitchen, or deep accumulated snow is not the same structure as a light sitting deck, even at the same surface dimensions. The materials list follows the structure. If the use changes, the frame and footings must be revisited before the board count is celebrated as finished.

Finally, consider wood treatment and product suitability for Canadian weather exposure, including freeze and thaw cycles, strong summer sun in some regions, and long wet shoulder seasons in others. Follow the board and lumber product instructions for spacing, ventilation under the deck, and fastener compatibility. Treated lumber and certain fasteners must be compatible, and the product literature, not habit, is the source for that pairing.

FAQ

How many deck boards do I need for a rectangular deck?

Divide the width the boards must cover by the actual board width plus the gap. In the worked example, 3.6 m divided by 0.145 m per board, which is a 140 mm board plus a 5 mm gap, equals 24.83, rounded up to 25 boards. Then multiply the board count by the board length to get total length, and add a stated allowance for cuts and selection. If your board width, gap, or direction changes, the count changes with it.

Why do calculators disagree with each other?

They usually disagree because they assume different things, not because one is broken. One tool may use nominal board width with no gap, another may use actual width with a gap, and a third may add a waste percentage without showing it. Diagonal layouts, borders, and stair treads are included in some estimates and left out of others. The fix is to compare assumptions, not just totals. Use the step by step method in this guide to see which assumption explains the gap between two results.

How many screws will a deck surface use?

Count joist crossings first, then multiply. For a straight layout, crossings per board equals the number of joists. Multiply crossings by screws per crossing, usually 2 for face screwed boards, and then by the number of boards. The worked example gives 13 crossings, 2 screws each, and 25 boards, for a total of 650 surface screws. Hidden fastener systems are counted differently, so follow that system instructions instead of reusing a face screw total.

Do I need a permit for a deck in Canada?

It depends on your municipality, the deck height and size, and whether it attaches to a house, among other local factors. There is no single national answer that an estimator can give for every property. Check with your municipal building department before you build, and ideally before you finalize the structure that your materials list is based on. Permit requirements can affect footings, railing, and stairs, which in turn affect quantities.

Can I use the same joist spacing for every board type?

No. Suitable spacing depends on the board product, its thickness and material, the joist span, and whether boards run straight or diagonally. Use the board manufacturer spacing guidance and your approved deck design as the source. The 400 mm centres in the worked example illustrate the counting method only. Changing spacing changes both the joist count and the screw count, so update the whole list when spacing changes.

How much extra lumber should I order?

Order extra on purpose, and write down why. A straight deck with few cuts needs less extra than a deck with stairs, borders, and many post notches. The allowance covers cutting waste, trimming, and rejecting a board that does not belong in a visible place. Many builders plan a percentage allowance and then round up to whole boards in the lengths they are actually buying. Keep the allowance visible on the list so it is not mistaken for the base count later.

Calculators and next steps

Estimate your surface boards and layout with the deck calculator: https://mississippimaple.ca/tools/deck.html

Check footing counts and concrete volume with the footings tool: https://mississippimaple.ca/tools/footings.html

Working with rough lumber or comparing board measure? Use the board feet tool: https://mississippimaple.ca/tools/board-feet.html

Compare lumber quantities and build your list totals with the lumber cost tool: https://mississippimaple.ca/tools/lumber-cost.html

Next steps: confirm the design and permit path locally, measure the deck in metres, fix board direction and actual board width, run the board, joist, and screw steps in order, add footings from the frame plan, and only then price the list. A list built in that order can be checked by anyone, including a lumber yard, in a few minutes.

Sources and figures

Board spacing, gap, and fastener guidance: deck board manufacturer installation instructions for the specific product selected. Structural, footing, railing, and permit requirements: National Building Code of Canada, provincial building codes, and your municipal building department. Lumber dimensions: lumber supplier and product labelling for actual versus nominal sizes. Worked example dimensions and counts are stated assumptions with arithmetic shown in full, not published statistics.

Estimates only, verify before you buy materials. This guide plans quantities and costs; it does not replace local building codes, manufacturer instructions, or professional advice.