| Item | Priced by | Scales with area? |
|---|---|---|
| Decking boards | Square foot of surface | Yes — this is the one item that genuinely does. |
| Framing (joists, beams) | Span, spacing and load | Partly — but spans and sizes step up, not smoothly. |
| Footings | Number and depth | No — driven by the framing plan and loads. |
| Posts | Height and count | No — driven by height above grade. |
| Stairs | Rise, run, landings | No — a raised deck needs a long flight regardless of size. |
| Railing | Linear foot of perimeter | No — perimeter grows more slowly than area. |
| Guards and handrails | Height above grade triggers them | No — a threshold requirement, not a gradual one. |
| Lateral bracing | Height | No. |
| Ledger and flashing | Linear foot of house attachment | No. |
| Demolition of an old deck | Size and construction of the old deck | Partly. |
| Site access | How hard it is to get materials in | Not at all. |
| Engineering | Whether the design triggers it | No — a threshold, notably height over six feet in Boise. |
| Height band | What it triggers |
|---|---|
| At or near grade | Shortest posts, simplest framing, no guard requirement in most configurations, minimal or no stairs. The cheapest deck per square foot by a clear margin. |
| Above 30 in. above grade | Boise's submittal checklist requires guardrail height and member spacing to be specified — guards become a design and cost item. |
| Raised, under six feet | Longer posts, more substantial framing, lateral bracing, a full stair flight with its own footings, and usable space beneath that may want finishing. |
| Taller than six feet above grade | Boise requires structural calculations stamped and signed by an Idaho licensed engineer — an added design cost on top of the construction cost. |
Height also drives buildability. A raised deck means working at height, more temporary support during construction, and more difficulty moving materials into position — all of which appear in labour rather than in any material line.
- A simple rectangle is the most efficient thing to frame and deck. Boards run full length with minimal cutting and waste.
- Angled corners introduce mitred cuts in both framing and decking, plus additional blocking to support board ends.
- Curves require either specialised material or substantial framing work, and produce significant waste.
- Multiple levels mean a second framing system, additional footings, and a set of steps between them with its own guard requirements.
- Picture-frame borders need blocking under every border joint — a visual upgrade with real framing implications.
- Inset features such as planters, benches or a hot tub area need framing designed for the load and the opening.
What to ask instead of “what is it per square foot?”
Ask about the structure
- How many footings, at what depth, and what size?
- What joist size and spacing, and what span?
- How is the ledger attached and flashed to the house?
- Is engineering required, and is it included?
The substructure is invisible once decked and is where a cheap deck is usually cheap.
Ask about the perimeter and vertical
- How many linear feet of railing, and which system?
- How many stair treads, and does the flight need a landing?
- Is fascia included?
These are the items that make two same-size decks differ most in price.
Ask about the site
- How will materials reach the build area?
- Is there an existing deck to demolish and dispose of?
- Does anything need to be protected, moved or reinstated?
Access constraints are pure labour and appear in no material list.
Ask about what happens after
- Is an electrical receptacle included?
- Who pulls the permit and schedules inspections?
Idaho's amended NEC requires a receptacle within the perimeter of a deck of 20 sq ft or more that is accessible from inside the dwelling.
That last point is a genuine Idaho-specific requirement rather than a nicety: IDAPA 24.39.10 amends NEC 210.52(E)(3) so that balconies, decks and porches of 20 square feet or more accessible from inside the dwelling must have at least one receptacle within the perimeter, positioned no more than 6½ feet above the surface.
Mistakes that cost the most
1.Budgeting from a per-square-foot rate found online
Those rates almost always describe a low, simple, rectangular deck. Applying one to a raised deck with stairs understates the cost badly.
2.Designing a long narrow deck without accounting for perimeter
Railing is priced by linear foot. A long thin deck can cost noticeably more than a square deck of identical area.
3.Treating stairs as a detail
A stair is a small structure with its own footings, stringers, guards and handrails, and it adds no usable deck area.
4.Not mentioning a possible hot tub until after the framing plan
The concentrated load has to be designed for. Adding support later means working beneath a finished deck.
5.Assuming a deck under six feet needs no engineering
Height is one trigger. Designs or materials not addressed in the IRC are another, and that catches unusual layouts and products.
6.Ignoring site access when comparing bids
A builder who has seen a narrow side gate prices the labour honestly. One who has not will find it later.
Why is deck cost per square foot misleading?
Because several of the largest cost items in a deck do not scale with its area. Stairs are priced by rise and run, not by deck size. Railing is priced by linear foot of perimeter, and perimeter grows more slowly than area as a deck gets bigger. Footings are priced per footing, and their number is driven by the framing plan and the loads rather than by square footage. Height above grade affects everything — posts, bracing, guard requirements and access — without changing the floor area at all. A per-square-foot figure derived from a low, simple, rectangular deck will always understate a raised deck with stairs and a complex outline.
Does a raised deck cost more than a ground-level one?
Substantially more, for the same area. Height drives longer posts and more substantial framing, more footing depth and often larger footings, guard requirements, stairs with their own footings and framing, and lateral bracing. It also complicates access for the build itself. In Boise, the City's residential submittal checklist requires structural calculations stamped and signed by an Idaho licensed engineer for any deck taller than six feet above grade, or for designs and materials not addressed in the International Residential Code — so height can add a design cost as well as a construction one.
How much do stairs add to a deck?
More than most homeowners expect, because a stair is a small structure in its own right. It needs its own footings, stringers cut to a consistent rise and run, treads, a landing where the run is long, and guards and handrails. A short flight from a low deck is a modest item. A long flight from a raised deck, with a landing and a turn, can be one of the largest single line items in the project — and it adds nothing to the deck's usable area, which is exactly why a per-square-foot figure hides it.
Why does railing cost so much?
Because it is priced by linear foot of perimeter and because the systems vary enormously in cost. A simple wood guard is at one end; cable, aluminium and glass systems are at the other, and the difference across a long perimeter is significant. Two decks of identical area can have very different perimeters depending on shape — a long, narrow deck has considerably more edge than a square one of the same area. Boise's submittal checklist requires guardrail height and member spacing to be specified where a deck is more than 30 inches above grade.
What is the single biggest deck cost variable?
Height above grade, because it drives so many other items at once — post length, framing size, footing depth, guard requirements, stairs, bracing and buildability. After height, the biggest variables are the decking material, the railing system, and the complexity of the outline. A simple rectangle is materially cheaper to frame and deck than the same area with angles, curves, multiple levels or a picture-frame border, because complexity multiplies cutting, waste and framing detail.
Do I need a permit for a deck in Boise?
Decks are permitted work in Boise, and the City publishes a specific submittal checklist for them requiring a site plan, a framing plan showing footings, posts and joist type, size, spacing, span and direction, elevations showing height, and section views cut from the bottom of the footing through the deck and railing. Structural calculations stamped by an Idaho licensed engineer are required for decks taller than six feet above grade or for designs or materials not addressed in the IRC. Other Treasure Valley jurisdictions administer their own requirements, so confirm with the one issuing your permit.
Each reference below is cited for a specific claim on this page. Codes, fees and product specifications change — confirm current requirements with the authority having jurisdiction before relying on them for a project decision.
- City of Boise — Residential Addition, Alteration & Accessory Building Submittal Checklist (#406)
Cited for: Boise's deck submittal requirements: site plan, framing plan, elevations and section views; guardrail specification where a deck is over 30 in. above grade; and stamped structural calculations for decks taller than six feet above grade or using designs or materials not addressed in the IRC.
- Idaho DOPL — Idaho Adopted Codes
Cited for: That Idaho enforces the 2018 International Residential Code with Idaho amendments, which governs residential deck construction.
- Idaho Administrative Code IDAPA 24.39.10 — Rules of the Idaho Electrical Board
Cited for: Idaho's amended NEC 210.52(E)(3) requiring at least one receptacle within the perimeter of a deck of 20 sq ft or more accessible from inside the dwelling, no more than 6½ ft above the surface.