Pricing a Deck: Boards, Rail, Footings and Stairs

Three numbers live on the same stick

One two-by-eight at fourteen feet is three quantities at once. It is fourteen lineal feet, it is 18.67 board feet, and it is one piece. Which of the three you are being charged in depends entirely on what is being sold. Dimensional softwood in North America usually comes off a per-piece list organised by section, length and grade. Rough-sawn timbers, glulam and hardwood decking are commonly quoted per board foot. Rail, fascia, trim and hidden-fastener track are quoted per metre or per lineal foot — and merchants say lineal where the rest of the world says linear, meaning exactly the same thing.

A board foot is a volume: nominal thickness in inches, times nominal width in inches, times length in feet, divided by twelve. The word carrying all the weight there is nominal. A board sold as a two-by-eight measures about an inch and a half by seven and a quarter once it has been through the planer, and those dressed sizes are not folklore — they are set out in the US Department of Commerce Voluntary Product Standard PS 20, the American Softwood Lumber Standard, with the European equivalents in BS EN 1313-1 for sawn softwood sizes and deviations and BS EN 336 for structural sections. The charge is levied on the size printed on the tag, not the size you can measure. Sixteen joists at fourteen feet is 224 lineal feet, which is 299 board feet at the nominal section and 203 board feet if you take a tape to the timber that turns up. Estimate off the tape and you arrive a third short of the figure the yard is going to invoice.

Because the conversion factor for any given section is a constant, the whole thing is a lookup you can hold in your head. Board feet per lineal foot is just the nominal cross-section in square inches divided by twelve, which is why two-by-six is the section everyone reaches for as a sanity check: one lineal foot of it is exactly one board foot, and every other section is a ratio against that. Learn the column and a stick list converts to a board-foot order between the van and the trade desk.

Where board-foot pricing genuinely bites is hardwood, and there the rules are somebody else's. The National Hardwood Lumber Association's Rules for the Measurement and Inspection of Hardwood and Cypress govern the quarter-inch thickness notation on the ticket — four-quarter, five-quarter, eight-quarter — and govern measurement at the rough size, before surfacing. Random-width hardwood decking is also sold on the tally: the yard counts the bundle, and that count is what appears on the invoice, not the count you calculated. Your board-foot figure is the order. The tally is the bill. Ask whether the tally is taken rough or surfaced before the timber is loaded, because afterwards it is a conversation about somebody's memory.

The frame is a stick list long before it is a board-foot number

The tempting shortcut is to go from deck area straight to board feet with a rule of thumb, and it fails for a reason that has nothing to do with the rule. Timber arrives in even stock lengths, and you buy the whole stick whatever you do with it. A joist that needs to be thirteen feet is a fourteen-foot purchase, and the foot you cut off has been paid for. So the frame is a count of pieces first, and only becomes a volume afterwards, if the price list happens to want one. Reverse that order and you have quietly averaged away every offcut in the job.

Nesting is where the money actually sits. Four rail posts cut at four feet come out of one twelve-footer with nothing left; blocking at fourteen and a half inches comes six from an eight-foot length with change. A cut list that nests well leaves a bag of ends. One that nests badly — a schedule full of nine-foot members ordered as ten-foot stock — leaves the better part of a stick in every bay, and no percentage added on top will find that money back, because it was never a percentage. It is a remainder, and remainders are lumpy. This is also the moment to notice whether any decking run exceeds stock length, because a butt joint is not just a cosmetic decision: it wants doubled blocking underneath it, and that blocking is another line on the frame order.

Grade and treatment split the order again, and the split is not optional. AWPA U1, the Use Category System, distinguishes ground contact from exposed above-ground service, and a post going into a hole is not specified the same way as a joist sitting clear of the earth. Buying the whole frame at the higher use category is money spent for nothing on most of the sticks; buying it all at the lower one puts untreated-for-purpose timber where the standard does not allow it. Two lines on the order, two rates, and the treatment category written against each. Price the field-cut preservative on the same order too: every cut end in treated stock needs it, and it is the line most reliably forgotten.

1. Take the member schedule off the drawing: section, count and cut length for joists, rim, ledger, beam plies, posts, blocking and stringers. Whether those sections are right is a structural question — AWC DCA 6, the Prescriptive Residential Wood Deck Construction Guide, or an engineer's calculation, not a price list.
2. Add bearing and overhang to every cut length before it becomes an order length. A joist is longer than its clear span, and a stringer is longer than the flight.
3. Nest each section's cut lengths into the stock lengths your merchant actually carries, and write down what falls out as drop. Do not average it.
4. Count pieces by section and by stock length. That count is the order for anything priced per piece, and it is finished at this point.
5. Convert only the sections your merchant prices by volume into board feet, at the nominal size, using the count and the stock length rather than the cut length.
6. Split the whole list by treatment use category before it is priced, so ground-contact stock is quoted separately from above-ground stock.

The metre lines, and why the plan shape sets them

Rail is the line that catches people out, and it catches them out in the same way every time. It is sold by the metre or the lineal foot, it frequently carries the highest per-unit-length rate anywhere on the job, and it has nothing whatever to do with floor area. It follows the perimeter of the open edges, and perimeter and area are only loosely related — loosely enough that the relationship between them is the biggest lever anyone has over this budget, and it gets pulled before anybody is asked for a price.

The arithmetic settles it in one line. Twenty-six square metres arranged as a square is a shade over five metres a side, so a bit more than twenty metres of edge. The same twenty-six square metres arranged two metres deep and thirteen metres long is thirty metres of edge — nearly half as much again, for identical floor. Tuck the deck into a corner so the house takes two sides and the open run collapses further still. None of that changes the board order by a single stick, and all of it changes the rail order, which is why the plan shape deserves ten minutes of arithmetic before it is agreed rather than after.

Rail is also not one rate. It is a per-length component and a per-post component, and quotes routinely blur the two. Post spacing is not a styling decision: IRC Table R301.5 requires a guard and its handrail to resist a concentrated load of 200 pounds applied in any direction at the top, and IRC Section R312.1.2 fixes the guard height for one- and two-family dwellings at not less than 36 inches, with the adopted edition governing. Every post is therefore a bolt group, a blocking detail, frequently a tension tie, and a hole in the fascia. Count the posts as a separate line from the metres, or the per-metre rate you derive is a fiction that will not survive being applied to a deck with more corners.

Fascia runs almost the same perimeter as the rail, less whatever the stair opening takes out, and is priced separately at a different rate — often in a different material altogether, since composite fascia over a treated frame is a common combination. When a quote says fascia is included, the question worth asking is what included covers: the board only, or the board with its stainless fixings and its mitred external corners. A mitred corner in composite is a labour item, and on a deck with a bay or an angled end there can be six of them.

Two rail quotes covering different runs are not comparable until each has been divided by the run it actually covers, and the same is true of a quote that bundles the stair rail with the deck rail against one that does not. Divide first, compare second. Keep the habit afterwards: when the invoices are in, divide your own totals by your own measured runs and file the result with the deck's dimensions beside it. A rate you measured beats a rate you were told.

Four denominators on one sheet

Assemble the total element by element rather than as one rate, and each element in the unit it was actually bought in. The point is not tidiness: a total built from four denominators can be interrogated afterwards. When the client asks for the deck a metre wider you can see which block moves, without re-pricing anything, because only one of the four will.

Once the four are on the sheet, the most useful thing on it is a ratio rather than a total: what share of the money the railing represents. On a small deck with three open sides it climbs faster than anybody expects, and once it is past about a third of the job the plan shape has become the budget. That is a design conversation, not a procurement one, and it is a far more productive conversation to have at that point than another round of asking three merchants for a better price on the same boards. The stairs behave the same way on a raised deck, where the riser count can quietly become the second largest line.

Contingency belongs on the sheet as a statement about what you do not know, not as a habit. A rectangular deck on level ground with the substructure visible and the ground already dug over is a low-uncertainty job. A deck over a slope, over an old patio nobody has lifted, or anywhere a drain run is suspected but not proven, is not, and the number should say so plainly rather than defaulting to whatever percentage got used last time. If the cut list nested cleanly and every box rounded up, say in the note that the contingency is for ground conditions only, so that a later reader does not add material waste to it a second time.

Finally, compute the cost per square metre — as an output, at the end, never as an input at the beginning. Record it alongside the deck's plan dimensions, its height above the landing point, its open-edge length and its footing count, because those four facts are the conditions under which that rate is true. Filed like that it becomes a genuinely useful benchmark for the next deck of a similar shape. Filed as a bare figure it becomes the thing that misprices the next deck of a different one.