Most Cost-Effective Deck Size by the Numbers


One of the “E’s” of E3 is Economical, so the question is put forth. What is the most cost-effective deck size? What size of deck gives you the most bang for the buck? The quick answer is

The most cost-effective wood deck size, 12’0” wide by 12’0” deep. This is the largest deck area with the least amount of material waste but still meeting IRC code. A 144 square ft deck, costing $700- 800 for material, roughly $5.20 per square foot. The most cost-effective deck size.

Of course, this is dependent on the season and where you source your lumber from. Lumber is a volatile commodity with pricing changing daily.

If you’re looking strictly for cost-effective, a 12’0” wide by 12’0” with the following specs

  • Ledger attached to the house
  • (10) 2×8 joist 16” on centre with 1’ cantilever
  • 3 ply 2×8 beam supported on two concrete piles
  • Less than 2’ above grade not requiring railing or stairs
  • Open below allowing ventilation and saving by not needing skirting material

Local code deck requirements may differ, so always check before building. That being said, most jurisdictions don’t require permits for decks less than 24” from grade.

A 12’0” wide by 12’0” deck will require the following material.

  • (11) 25 kg redi-mixed concrete
  • (2) 10” x4’ sono tube cut in half
  • (2) Galvanized concrete saddles for beam
  • (2) 10’ Galvanized deck flashing
  • (15) 2×8-12’ P.T.
  • (9) 2×8 galvanized joist hangers
  • (27) 5/4×5.5”-12’ Pressure-treated Radius edge decking
  • (523) 3” treated deck screws
  • (127) 3” galvanized ardox nails
  • (36) 1.5” galvanized hanger nails

With this list, you better not miscut any boards or drop or bend a nail. I would recommend adding a few extra nails and screws just in case. Selected your lumber at the store to ensure every piece is straight and free of defects. Running back to the store will cost you time and money.

The following are a few things I considered when deciding on the most effective deck size. Some are self-explanatory but still factored into the size of the deck. There are things I would highly recommend for a deck but are not included with this deck to keep the cost and material waste low.

Material Lengths Considerations

You may have noticed the deck size, are even numbers. Lumber and decking are sold at 2’ increments. To minimize waste the deck needs to be built without large offcuts of joist and decking. So, whatever size of deck you build, the most cost-effective is an even number.

Code Limitation for deck joist

The International Residential Code (IRC) allows 2×8 joist, 16” on centre spruce/pine/fir pressure-treated wood to span 11’1” between supports. Also, 2×8 joist can cantilever/overhang the beam, 1’10 when 16” on centre. Therefore, the most effective joist size is 2×8, with a beam 11’ on centre from the ledger with a 1’0” overhang. You can play around a little bit with the beam location as long as it is not more than 11’1” from the ledger, and the joist overhang is not more than 1’10,” but I find a one-foot overhang a convenient length.

Increasing the joist spacing to 24” would reduce the number of joists required but also reduce the allowable span both between the ledger and deck. Reducing the overall size of the deck while increasing material waste. Meaning 16” on centre joist spacing will give you the most deck.

On Centre Spacing of Joist

Consistent joist spacing allows you to get the most deck out of every joist used. 16” divides evenly into 8’, 12’ and 16’. Meaning the most effective deck width is one of those widths.  

Deck Beam Spanning

Reducing concrete piles, reduces material cost, saving roughly 6 bags of concrete per pile and hours digging. The IRC allows for a 3-ply 2×8 beam to span 9’5” between post centres when supporting 6’ of deck or less, also allowing a quarter of the beam span to overhang the post to a maximum of two feet. Therefore, you can support a deck twelve feet wide, with a three-ply beam overhanging 15” on each side. This is the minimum beam, with the least piles to support your deck.

But the IRC also allows a 3 ply 2×10 beam to span 11’9” between post centres when supporting 6’ or less of joists. Also, IRC allows beams to cantilever past the support one-quarter of the beam span to a maximum of two feet. In short, space the piles ten feet apart, and overhang the beam one foot on each side allows you to support the entire length of the deck with only two concrete piles. For an extra twenty or so bucks, you will get a stronger deck. I think this is worth the extra cost.

Deck height

Deck height is critical in reducing the decks’ cost. A low deck doesn’t need railing or steps. This will save you considerably in deck cost. Check your jurisdiction but most don’t require railing if your deck is less than 30 or 24 inches. In Alberta, where I build decks, it’s 24”. High enough to scare you if accidentally step off but low enough to not cause any serious harm.

The same can be said about steps. Steps will enhance your deck, but you can step up two feet. I would recommend steps meeting code with risers between 6 and 8 inches (150-200 mm), but you can do without if you need to reduce cost. Stairs with all their angles and cutting use a lot of material and time. Delete stairs, save money.

Deck Railing will Increase Cost

If we go to Home Advisors for some quick numbers, we read that wood railing is roughly $75 per foot. Aluminum railing roughly $80 a lineal foot. Railing on three sides of the deck, roughly 36’ will add $2 700 for wood or $2 880 for aluminum. That’s more money than the entire deck. Keep your deck low, avoid the cost of railing.

If you do put up railing, spend the extra and go with low maintenance aluminum. Just one-time sanding down your wood railing and staining will leave you wishing you had.

Dressing up your Deck Increase Cost

I like to dress up decking with picture framing. It hides the end cuts and gives the deck a nice finish. But to save cash, delete the picture frame. This will save you about forty bucks in material.

A 12’ by 12’ deck may be the most cost-effective, but we need to consider use. A cheap deck is not of much value if you can’t use it. I have written a fuller article on this but here is a quick recap.

Deck sizes requirements

  • 5’0 X 8’0” for barbequing, minimum
  • 14’0” X 16’0” for a rectangle table for 4-6 people to eat, minimum
  • 6’0” X 8’0” for two people to sit and relax, minimum
  • 19’0” X 16’0” for barbequing and eating, minimum

A 12’ by 12’ deck is limited in use. A little extra money, but still keeping material requirements to a minimum, maybe better.  You may be better of increasing the decks’ width to 16’. This will just give you a little more space to move. Set up a small table by your barbeque and actually enjoying your deck.

An alternative effective deck size to be considered

A 192 square ft deck, 16’0” wide by 12’0” deep, will cost slightly more. Costing roughly $1 000-1100 in material, about $5.50 per square ft but provides you with a more useable deck size.

Similar specs but designed to be 16’ wide by 12’ deep

  • Ledger attached to the house
  • 5/4×5.5” Pressure-treated Radius edge decking
  • 2×8 joist 16” on centre with 1’0’ cantilever
  • 3 ply 2×10 beam supported on three concrete piles
  • Less than 2’0” above grade requiring no railing or stairs
  • Open below allowing ventilation and not requiring skirting material

A 16’ wide by 12’ deck would require the following material.

  • (17) 25 kg redi-mixed concrete
  • (3) 10” x4’ sono tube cut in half
  • (3) Galvanized concrete saddles for beam
  • (2) 10’ Galvanized deck flashing
  • (5) 2×8-16 ‘P.T.
  • (15) 2×8-12’ P.T.
  • (11) 2×8 galvanized joist hangers
  • (27) 5/4×5.5” Pressure-treated Radius edge decking
  • (689) 3” treated deck screws
  • (156) 3” galvanized ardox nails
  • (88) 1.5” galvanized hanger nails

Meeting IRC requirements for decks but with just a little more room. The biggest difference with a 12’ wide deck is the one extra concrete pile

Whatever you decide, I hope you enjoy your deck. 16’ or 12’ wide, whatever is the most effective deck size for you. And sometimes, it’s worth it to spend a little more, but get a more enjoyable deck.

Ryan Nickel

A Red Seal carpenter, passionate about building decks to be enjoyed.

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