How much would a 20x20 deck cost?

A 20 by 20 foot deck is 400 square feet. At published 2026 cost-guide rates that is roughly $10,000 to $20,000 in pressure-treated or cedar. Composite runs closer to $16,000 to $32,000. Ironwood (ipe) runs about $22,000 to $32,000. Railings, stairs and a roof push those figures higher.

How much should a 12x24 deck cost?

A 12 by 24 foot deck is 288 square feet. Wood lands near $7,200 to $14,400 at national cost-guide rates, and composite near $11,500 to $23,000. A Seattle-market guide figure of $37 to $74 per square foot puts the same deck near $10,700 to $21,300. Where you land in that spread depends mostly on railing and height.

Is it cheaper to lay concrete or build a deck?

Usually concrete. Published guides put a poured patio at $5 to $15 per square foot installed. Stamped concrete runs about $9 to $30. A deck runs $25 to $80. The trade-off is grade. Concrete wants ground close to level, so a slab suits some island lots and a raised deck suits others.

Does composite really cost less than wood over time?

It can. A national cost report priced the same 16 by 20 foot deck two ways. Wood came in near $18,263 and composite near $25,096. Wood in a wet marine climate wants a fresh stain or seal every year or two. Whether that upkeep closes the gap depends on how long you keep the house.

Is ironwood decking worth the extra cost?

Ironwood, sold as ipe, is a dense tropical hardwood. Published guides put it at about $55 to $80 per square foot installed and up. We prefer it for its durability and its looks. It is what we reach for on a deck you see every day. On a back deck out of sight, cedar or composite usually makes more sense.

Is this what Culver Built charges for a deck?

No. Every figure here comes from published market research, not from our price list. Your price depends on the site, the framing height, the railing and any cover. We give free estimates. Call or text (360) 544-9027 and we will look at the deck site and put a real number on it.

How Much Does a Deck Cost in Washington? Composite vs Wood

Q: Do I need a permit to build a deck in Washington?

In unincorporated Island County a deck is exempt from a building permit only if four things are true. It stays under 200 square feet. It sits no more than 30 inches above grade at any point. It is not attached to a dwelling, and it does not serve the required exit door. Most decks miss at least one. Oak Harbor, Coupeville and Langley run their own building departments inside city limits.

Most decks in Washington run about $25 to $80 per square foot installed. National cost guides put pressure-treated and cedar decks near the low end, roughly $25 to $50. Composite sits around $40 to $80. Ironwood (ipe) is the top of the range at about $55 to $80 and up.

Multiply that out and a 20 by 20 foot deck lands near $10,000 to $20,000 in wood. The same deck in composite runs about $16,000 to $32,000. A cost guide written for the Seattle market puts deck work there at $37 to $74 per square foot. That is above the national middle. These are market numbers, not our price list.

What does a deck cost per square foot in Washington?

The table uses 2026 published ranges for material and labor together. The size columns are those ranges multiplied out for a simple deck.

Decking material	Installed cost per square foot	12x24 deck (288 sq ft)	20x20 deck (400 sq ft)
Pressure-treated wood	$25 to $40	$7,200 to $11,500	$10,000 to $16,000
Cedar	$30 to $50	$8,600 to $14,400	$12,000 to $20,000
Composite	$40 to $80	$11,500 to $23,000	$16,000 to $32,000
Ironwood (ipe)	$55 to $80 and up	$15,800 to $23,000	$22,000 to $32,000

Railings, stairs and a roof get priced on top of those numbers. On a view deck they add up fast. We build wood and composite decks across the island. A deck builder on Whidbey Island should price yours from the real site.

Does composite or wood cost more?

Wood costs less to install. It costs more to keep. Cedar and pressure-treated boards want a clean and a fresh stain every year or two. In a wet marine climate that upkeep is real work. Composite costs more up front and mostly wants a wash.

A national remodeling cost-versus-value report priced the same 16 by 20 foot deck two ways. Wood came in near $18,263. Composite came in near $25,096. That is about 37 percent more for the identical footprint.

We prefer ironwood, sold as ipe, for its durability and its looks. It is a dense tropical hardwood. Published guides put installed ironwood at about $55 to $80 per square foot and up, which is above composite.

What drives the price of a deck on Whidbey Island?

Railing type. This is the biggest single swing in the whole budget. Published 2026 ranges start near $15 to $30 per linear foot for composite railing. Wood runs about $40 to $50 and aluminum about $40 to $70. Glass runs $100 to $600. Cable railing is the usual pick on a water view. It runs about $50 to $200 per linear foot installed. Another guide puts a stainless cable system at $150 to $285.

Height and stairs. A deck two feet off the ground is simple framing. A deck off a second floor is not. One cost guide puts raised and second-story decks at $40 to $50 per square foot. The same guide says to expect 25 to 70 percent more than a ground level deck. Every flight of stairs adds framing, footings, treads and railing.

Covered sections. A roof over part of the deck is what makes it usable in a Whidbey winter. Published ranges for a deck cover run about $3,000 to $10,000. A cover also changes the framing under it, because the posts now carry a roof.

Footings and framing for island conditions. Island County fills in the state residential code table with a 97 mph basic wind speed. It marks topographic wind speed-up effects YES. Frost line depth is 12 inches, and that is the minimum footing depth below finish grade. Bluff lots and wind-exposed sites take more posts and bigger footings.

Salt air and wet winters. Decks near the water get corrosion-resistant hardware, and that hardware costs more than standard hardware. Flashing at the ledger is where water gets into a wall, so that detail gets extra care here.

Do you need a permit to build a deck in Island County?

Usually yes. In unincorporated Island County the building code exempts a deck only when four things are all true. It is no larger than 200 square feet. It is not more than 30 inches above grade at any point. It is not attached to a dwelling. And it does not serve the required exit door.

Most real decks miss at least one of those. A deck bolted to the house needs a permit. The county also states that being exempt from a permit does not allow work that breaks the code.

Inside the city limits of Oak Harbor, Coupeville or Langley, the city runs its own building department. Island County sets its building permit fee from the project valuation on its published fee schedule. The bigger the job, the bigger the fee. National guides put deck permits in the $350 to $1,800 range. Confirm the current numbers with the office that covers your address. Our guide to Island County building permits covers the rest of the submittal list.

Is it cheaper to pour concrete or build a deck?

Concrete is usually cheaper per square foot. Published 2026 guides put a plain poured patio at $5 to $15 per square foot installed. Stamped concrete runs about $9 to $30. A deck runs $25 to $80 over the same area.

The catch is the ground. A slab wants a surface close to level, with a base and drainage under it. On a sloped or wooded island lot, a deck buys you a flat floor without moving much dirt. If your grade is friendly, a stamped concrete patio or a paver patio can cost less and last a long time. In unincorporated Island County a patio slab or a walkway does not need a building permit. A deck attached to the house does.

What should you do with these numbers?

Treat them as a range check. Your own number comes from your own site. The spread between $25 and $80 per square foot is mostly railing, height, stairs and cover. Decide those four things and the price gets real fast.

We give free estimates. Call or text (360) 544-9027. We will look at the deck site and talk through material and railing. Then we put a number on it. See how we build custom decks on Whidbey Island, from ironwood to cable railing on a view deck.