How to estimate a deck from counts, then check it by the square foot
To estimate a deck, draw the frame and count it: footings, posts, beam, ledger, joists, hangers, deck boards and fasteners, plus stairs and railing if the height calls for them. Price each count, add crew days at what a crew day really costs, and set the price at cost divided by (1 minus your margin). The 12 by 16 foot pressure treated deck worked out below prices at $6,575, about $34 a square foot. Square foot pricing is a check on the answer and not the method, because two decks of the same area can differ by a flight of stairs, 40 feet of railing and three extra footings.
Step by step
- Draw the deck and settle the height. Get the size, the height of the door threshold above grade, and where the stairs will land. Height drives almost everything: under the model residential code a walking surface more than 30 inches above grade needs a guard at least 36 inches high, and a stair with four or more risers needs a handrail. A deck at 28 inches and a deck at 34 inches are different estimates.
- Check the permit and the ledger wall. The model code only exempts a deck from a permit when it is 200 square feet or less, no more than 30 inches above grade, not attached to the house and not serving the required exit door, and many towns are stricter. Look at what the ledger would fasten to, because the code does not allow a ledger to be supported on brick or stone veneer. Call 811 before any digging, since every state requires the utility locate.
- Count footings, posts and beam. Lay out the beam, then space posts under it from the span table your building department uses. Each footing gets a form at $8.60 and bags of concrete at $7.60, and the bag count follows frost depth, which can be several feet down in cold regions. Posts are $12.75 for a pressure treated 4x4 and $28.50 for a 6x6, with a post cap at $12.50 on each.
- Count the ledger, joists and hangers. Divide the deck length by the joist spacing and add one, so 16 feet at 16 inches on center is 13 joists. Pressure treated 2x8 joist stock runs $1.88 a foot, each joist needs a galvanized hanger at $1.58 where it meets the ledger, and the ledger gets flashing at $1.58 a foot plus half inch lags, bolts or approved structural screws. The ledger has to be at least a 2x8 and no smaller than the joists hanging from it.
- Check the joist span before you count lumber. The IRC deck table puts a southern pine 2x8 at 16 inches on center at a maximum span of 11 feet 10 inches under a 40 pound per square foot live load, and the number changes with species and spacing. A 12 foot joist therefore needs the beam set in from the rim, with the tail cantilevered, or a jump to 2x10. Settle that on paper, because it changes the lumber list and the footing layout.
- Turn the surface into linear feet of decking. A nominal 6 inch deck board covers 5 and a half inches plus the gap, so figure a little over 2.1 linear feet of board per square foot. Pressure treated decking is $1.68 a foot and composite carries about a $3.90 a foot allowance, which makes the same 192 square feet roughly $690 in treated boards or $1,600 in composite before waste. Add 5 to 10 percent for square layouts and more for diagonals or picture-frame borders.
- Price stairs and railing as their own units. Stairs are stringers at $22.50 each, treads and a pad to land on, and the total rise has to divide into risers no taller than 7 and 3/4 inches with treads at least 10 inches deep. Railing is the line that surprises people: composite railing carries a $32.50 a foot allowance, so 40 feet of guard is $1,300 in material before a post is set. Never fold either one into a square foot rate.
- Figure crew days, divide by margin, write the assumptions. Think in days by phase: layout and footings, framing, then decking, stairs and rail, with a low 12 by 16 at about three days for two people. Lumber, hardware and labor together are the cost, and a 35 percent margin means $4,274.06 divided by 0.65, or $6,575. On the estimate, state the size, height, framing lumber, decking product, footing count and depth, and who pulls the permit, and exclude rock in the footing holes and repairs to the house wall found when the siding comes off.
The deck pricing formula
Footings, posts and caps, plus beam, ledger and joist footage, plus hangers, flashing and structural fasteners, plus decking footage with waste and screws, plus stairs and railing, equals materials. Labor is crew days times crew size times 8 hours times what a loaded hour costs you. Divide the two together by (1 minus margin) and pass the permit fee through on its own line. At 35 percent, $4,274.06 divided by 0.65 is $6,575.48, while the same cost times 1.35 is $5,769.98, which is $805.50 short and works out to a 26 percent margin.
A 12 by 16 foot pressure treated deck attached to the house, 20 inches off grade, with a three-riser stair. Framing is 220 feet of 2x8 joist stock (a 16 foot ledger, 13 joists at 12 feet, a 16 foot rim and a doubled 16 foot beam set 18 inches in from the rim) at $1.88, or $413.60, with 13 joist hangers at $1.58 for $20.54, 16 feet of ledger flashing at $1.58 for $25.28, and 3 pounds of structural screws at $8.50 for $25.50. Two 6x6 posts at $28.50, cut into four short posts, is $57, with four footing forms at $8.60 for $34.40, 16 bags of concrete at $7.60 for $121.60 and four post caps at $12.50 for $50. Decking is 26 rows of 16 footers plus two spares for culls and stair treads, 448 feet at $1.68, or $752.64, with 10 pounds of deck screws at $6.60 for $66 and three stair stringers at $22.50 for $67.50. Materials total $1,634.06. Two carpenters for three days is 48 hours, and at a loaded $55 an hour labor is $2,640. Job cost is $4,274.06. Sold at a 35 percent margin, that is $4,274.06 over 0.65, which comes to $6,575.48, so quote $6,575, about $34 a square foot, with the permit fee passed through on its own line.
Cost factors deck builders price for
Height above grade
Past 30 inches the deck needs guards, and at four risers the stairs need a handrail, so a tall deck buys railing, longer posts, bracing and slower work off ladders. Tall decks also tend to draw a closer plan review. Price the frame you drew, not last month's low deck.
Decking material
Composite at a $3.90 a foot allowance is more than double treated decking at $1.68, and it often wants tighter framing. Trex, for one, calls for joists at 16 inches on center for straight runs and 12 inches when boards cross at 45 degrees. Hidden fastener systems add material and time, so read the manufacturer's install guide before you count joists.
Attached or freestanding
A ledger saves a beam and a row of footings, but it has to be flashed, fastened on a schedule and tied to a solid band joist. Veneer walls, cantilevered floors and questionable rim boards push you to a freestanding frame with its own beam at the house. The model code lets freestanding deck footings stop above the frost line, though local amendments vary, so ask first.
Soil, slope and digging
Footings in rock, roots or fill take hours instead of minutes, and a sloped yard means posts of different lengths and a harder layout. Buried utilities move footings and sometimes the whole deck. Probe the footing spots during the site visit and write an hourly adder for rock into the contract.
Stairs, landings and extras
A three-riser stair is a few stringers and an hour or two. A full flight with a landing is a small deck of its own with its own footings. Skirting, benches and lighting belong on separate lines, because each one is easy to give away when the customer asks for it on build day.
Frequently asked questions
When does a deck need a railing?
Under the model residential code, a guard is required when the walking surface is more than 30 inches above the grade below. The guard has to be at least 36 inches high, and its openings cannot pass a 4 inch sphere. Stairs with four or more risers also need a handrail. Some jurisdictions set stricter numbers, so check locally before you price the rail.
Do I need a permit to build a deck?
Usually, yes. The model code exempts only decks that are 200 square feet or less, no more than 30 inches above grade at any point, not attached to a dwelling and not serving the required exit door, and all four have to be true. Most decks off a back door fail the last two. Local rules can be tighter, so call the building department and put the fee and the inspection trips in the estimate.
How many deck boards do I need per square foot?
A standard deck board is 5 and a half inches wide, and with a gap it covers about 5 and 5/8 inches, which works out to roughly 2.13 linear feet of board per square foot of deck. A 192 square foot deck needs about 410 feet before waste. Order by rows and board lengths instead of total footage so the butt joints land where you want them.
Can I attach a deck ledger to brick?
Not to veneer. The model residential code says deck ledgers shall not be supported on stone or masonry veneer, because the veneer is a skin and not structure. The usual answers are a freestanding deck with its own beam and footings next to the house, or an engineered connection through the veneer to the framing. Either one changes the estimate, so identify the wall while you are on site.
Is there an app that writes up a deck bid from the yard?
Staxen's estimator, Eddie, does. Talk through the size, height, decking, stairs and railing, and Eddie builds the line-item estimate with prices for you to check, then it goes out by text for e-signature and a deposit. Josie can put the build on the schedule with SMS reminders and send a change order when the customer adds a bench or a second stair. You pay $59 per month for each AI employee you hire, with all three at $149 per month, and the app gives you the first 7 days free.