Composite deck cost calculator

A 20x20 composite deck is 400 square feet and costs $12,260 to $16,590 installed at national-average rates, about $36.06 per square foot all-in. The same 400 square feet in pressure-treated pine, the standard benchmark, runs $9,210 to $12,460. Both totals include framing, railing, a short flight of stairs, hardware, permit and labor, and both move by up to 35% once your state's labor rate is applied.

A 16x20 composite deck is 320 square feet and costs $10,190 to $13,780 installed, or roughly $37.45 per square foot. The surface alone takes about 50 16-foot boards including waste, at $9 per square foot for the boards, $2,880 before framing, railing or labor.

A 14x20 composite deck is 280 square feet and costs $9,150 to $12,380 installed. Dropping from a 16x20 to a 14x20 removes 40 square feet but only about $1,220 of cost, because the permit, the ledger connection and the stairs are fixed no matter how large the deck is. Per square foot the smaller deck is actually slightly more expensive at $38.45 against $37.45.

Trex is priced by tier rather than as a single number. Enhance Basics sits around $5 per square foot for boards only, Select around $9, and Transcend, the premium line, around $12. Our calculator prices composite at a blended $9 per square foot for boards, which lands between Select and Transcend. TimberTech, Fiberon and Deckorators compete at each of those tiers, and installed cost differs far less than board price does, because framing, railing and labor are identical whichever brand goes down.

The decking boards, at about 22% of the installed total on a 192-square-foot composite deck, $1,728 of $7,997. Railing is next at $1,470. The substructure (joists, beams, posts and footings) accounts for roughly 12% of the total and is invisible the moment the deck is finished. Taking the railing off drops the project by $1,470, about 18%, which makes it the easiest place to trade down. Across the whole job, installation labor is 40-50% of what you pay.

Divide the deck area by the coverage of one board. A 16-foot board 5.5 inches wide covers 7.3 square feet, so a 320 square foot deck needs 44 boards on paper and about 50 ordered, once the 12% cut-and-damage allowance is added. For a 400 square foot deck that becomes 62 boards. Diagonal decking adds roughly 15% on top of that, because every board meets the joists at an angle and every cut is a waste piece.

A composite deck lasts 25-30 years. Maintenance requirement: wash occasionally; never needs sealing. Across that service life the 192-square-foot deck above works out to roughly $291 per year against $502 for pressure-treated pine, which is a fairer comparison between materials than the upfront price. The substructure usually outlives the surface, so a resurfacing at year 15 or 20 is a real option on a well-built frame.

The most common upgrade choice, low maintenance at a price most homeowners will accept. Advantages: No sanding, staining or sealing for the life of the deck; Will not splinter, rot or attract insects; Modern capped boards hold color and resist stains well. Drawbacks: Roughly 2.5x the board cost of pressure-treated; Gets hot underfoot in direct sun, especially in dark colors; Cannot be sanded or refinished if it is scratched. Against pressure-treated pine, the standard benchmark, this deck costs about $1,724 more upfront, or $291 per year of service against $502.

Yes, this is a realistic DIY project for someone comfortable with framing. A DIY build costs about $6,185 against $7,997 installed, saving roughly $1,812. Budget three to four weekends, and check every corner with the 3-4-5 rule before fastening. The ledger attachment to the house is the one detail worth having inspected regardless of who builds it.

More than most people expect. The deck above uses 42 linear feet of railing; removing it entirely drops the total from $7,997 to $6,527, a difference of $1,470, or about 18% of the project. Railing is priced per linear foot and is independent of decking choice, so it is the easiest place to trade down. Code requires it above 30 inches of drop in most jurisdictions, so a ground-level deck can skip it entirely.

Substantially, because height changes the substructure rather than the surface. Ground level is the baseline; 2 to 4 feet adds about 10%, 4 to 8 feet about 25%, and over 8 feet about 45%. The same deck costs $7,633 at ground level and $9,270 above 8 feet. Height also triggers the railing requirement and, past 30 inches, the permit in most jurisdictions.

A residential deck is engineered to carry 50 lbs per square foot: 40 psf of live load for people and furniture, plus 10 psf of dead load for the structure's own weight, under IRC Table R301.5. On a 12x12 deck that is 5,760 lbs of people and belongings against a 7,200 lb total design load, and on a 16x20 deck 12,800 lbs of live load. Those numbers only hold if the framing was built to match: joist size and spacing, beam span, post size and footing bearing all have to carry it, and the ledger connection to the house is the component that actually fails. A hot tub is the common trap, filled and occupied it concentrates 100 psf or more in one spot, and it needs framing designed for it rather than a standard deck.

The 3-4-5 rule is how builders check that a corner is square before anything is fastened down. Measure 3 feet along one edge, 4 feet along the edge meeting it, and the diagonal between those two marks should be exactly 5 feet, if it is longer the corner is open, if it is shorter the corner is closed. It is the Pythagorean theorem used as a site tool, and it scales: 6-8-10 or 9-12-15 give a more accurate result on a large deck because the error is spread over a longer measurement. Check the ledger and the outer beam this way before you set a single joist, because a frame that is out of square puts every deck board out of parallel with the house.