Planning a deck comes down to making decisions in the right order: what the deck is for, what your local rules allow, how big it should be, how it will be framed, and what it will be built from. Get those settled on paper and the materials list, the budget and the permit drawings almost write themselves. Skip ahead to picking boards before you know the frame, and you usually end up redrawing.
This guide walks through the sequence I use with homeowners, with a running example of a 16 × 12 ft deck attached to the back of a house.
Step 1: Decide what the deck needs to do
Start with how you will use the space, not with a number. A deck for a grill and two chairs is a very different build from one that seats eight for dinner.
Make a short list:
- Activities. Dining, lounging, grilling, a hot tub, a path to the yard.
- Furniture. Measure the table, chairs, grill and loungers you actually own or plan to buy.
- Traffic. Where people walk from the door to the stairs. That path should stay clear of the table.
- Sun and shade. Note where the shadows fall in the afternoon. It affects comfort and, for composite boards, surface heat.
Then lay it out on the ground. Put the real furniture on the lawn, pull the chairs back as if someone is sitting in them, and mark the outline with stakes and string. In my experience this ten-minute exercise is the most reliable sizing tool there is. People who skip it tend to build a deck that looked big on paper and feels cramped with a table on it.
For our example, a 6-ft table with chairs plus a grill corner fits comfortably in 16 ft along the house and 12 ft out.
Step 2: Check the rules before you draw anything final
Several rules can change your size and position, so look them up early.
Permits
Most attached decks need a building permit. The IRC model code exempts some small decks, but the exemption is narrow: as Angi summarizes it, decks under 200 sq ft and less than 30” above grade, not attached to the house and not serving a required exit door often qualify. A 16 × 12 deck is 192 sq ft, but because it is attached to the house it would usually still need a permit. Your city or county decides, and many have amended the model code, so call the building department before you finalize anything.
Setbacks, easements and HOA rules
Zoning setbacks control how close the deck can sit to property lines. Easements may forbid footings in a strip of your yard. HOAs can dictate materials and colors. Get these from your plat or survey, the zoning office and your HOA documents.
Buried utilities
Call 811 before you dig footings. Gas lines, electric feeds and irrigation often run right where a deck goes.
Step 3: Choose location, height and attachment
Height sets the complexity
Deck height drives a lot of the cost and code work. Under the 2021 IRC, guards are required on open sides of walking surfaces more than 30” above the floor or grade below, and they must be at least 36” tall with openings that will not pass a 4” sphere (City of Lake Stevens IRC R312 handout). A low deck may need no railing at all; a deck off a raised first floor will need railing, taller posts and more stairs.
Attached or freestanding
An attached deck hangs one side on a ledger bolted to the house rim joist. A freestanding deck uses a second beam and row of footings near the house instead. Ledgers save footings but need careful flashing and the right fasteners; freestanding decks avoid penetrating the house wall. The ledger vs freestanding guide covers the trade-offs.
Our 16 × 12 example sits about 24” above grade, attached with a ledger, so it falls under the 30” guard threshold. Local codes vary, so confirm with your building department before you leave the railing off.
Step 4: Size the deck to board lengths
This is where a lot of plans waste money. Deck boards come in fixed lengths, and the deck dimension that runs parallel to the boards should work with those lengths.
Most composite boards are sold in 12, 16 and 20 ft lengths (TimberTech installation guide), and pressure-treated decking is commonly stocked in even lengths as well. On our example, the boards run parallel to the house, along the 16 ft side. A 16-ft board covers each row in one piece, with no butt joints.
Change that deck to 17 ft along the house and every row now needs a joint, or a 20-ft board with 3 ft cut off. That one foot raises the board cost and adds seams that must land on doubled joists, according to the same TimberTech guide.
Counting rows for the 12-ft depth:
- 12 ft = 144”
- Board width 5.5” plus a 3/16” gap = about 5.69” per row
- 144 ÷ 5.69 ≈ 25.3, so 26 rows of 16-ft boards
Add a waste allowance on top. TimberTech’s own method adds 10%. Our deck board calculator does this row math for you and lets you compare lengths, including layouts that need seams.
Step 5: Sketch the framing
You do not need to be an engineer to sketch a frame, but you do need to follow the span tables your jurisdiction uses. The IRC includes prescriptive tables for joists, beams, posts and footings in section R507.
Joists
Joists run perpendicular to the deck boards, so in our example they run from the ledger out 12 ft to the beam. For southern pine at 16” on center, the 2021 IRC table reproduced by Anne Arundel County allows:
| Joist size | Max span at 12” o.c. | Max span at 16” o.c. |
|---|---|---|
| 2x8 | 13’-1” | 11’-10” |
| 2x10 | 16’-2” | 14’-0” |
A 2x8 at 16” o.c. falls just short of a 12-ft span, so the plan either moves to 2x10s, tightens spacing to 12” o.c., or pulls the beam in and cantilevers the joists past it. Spans differ by species and grade, so use the table your county adopts.
Joist count along the 16-ft ledger at 16” o.c.: 192” ÷ 16 = 12 spaces, so 13 joists. The deck framing calculator handles joist counts. Composite boards and diagonal layouts often call for 12” spacing instead, so check the decking manufacturer’s guide.
Beam, posts and footings
The beam carries the outer ends of the joists and sits on posts and footings. Footing size depends on how much deck area each one supports. In the same Anne Arundel guide, a footing carrying 60 sq ft of deck needs an 18”-diameter round footing 6” thick, at 50 psf and 2,000 psf soil. Footings must also go below your local frost depth, which ranges widely across the country. Use the deck footing calculator for sizes, and ask your building department for the required footing depth before you dig.
Step 6: Plan stairs and railings
Stairs take up more yard than people expect. The IRC caps riser height at 7-3/4” and requires a minimum 10” tread depth (We Know Codes stair geometry summary). For our 24” deck, 24 ÷ 7.75 = 3.1, so you need 4 risers of 6” each and 3 treads. At about 10.5” per tread, the stairs project roughly 32” from the deck, plus a landing pad at the bottom.
Mark the stair landing on your ground layout so it does not dump people into a flower bed. The deck stair calculator works out riser count and stringer length.
Step 7: Choose materials and set a budget
With the size and frame settled, you can price it. Material choice has the biggest effect on the decking line. For 2026, Ergeon puts installed decks at about $25 to $40 per sq ft for pressure-treated wood and $35 to $55 for mid-grade composite. For our 192 sq ft deck, that is roughly $4,800 to $7,700 in pressure-treated and $6,700 to $10,600 in composite, before local variation. Prices in your area may be well above or below these national ranges.
The deck cost breakdown splits a quote into its line items, so you can see where the money goes beyond the boards.
Step 8: Put it on paper
Before you request quotes or apply for a permit, assemble:
- Site plan. House outline, deck footprint, distances to property lines.
- Framing plan. Ledger, joists with size and spacing, beam, posts and footing locations.
- Elevation or section. Height, footing depth, guard height, stairs.
- Materials list. Boards by length, framing lumber, hardware, fasteners, concrete.
Many building departments publish a sample deck plan or a prescriptive deck guide. Following it closely usually speeds up review. The American Wood Council’s DCA 6 deck construction guide is a widely used reference for prescriptive wood deck details.
A note on scope: this site gives planning estimates, not engineering advice. Codes vary by jurisdiction, and your building department has the final word on what gets approved.
Frequently asked questions
How long does it take to plan a deck?
The design work itself can be done in a weekend once you know the rules. The slow part is usually the permit review, which depends entirely on your local building department’s workload. Start the permit conversation early if you want to build in spring.
What size deck should I build?
Size it around the furniture and traffic you expect, then adjust the dimension parallel to the boards to match a stock board length such as 12, 16 or 20 ft. Laying the furniture out on the lawn with string lines is the most reliable check. Bigger is not always better, since cost scales with area and height.
Do I need a permit for a small deck?
Possibly not, but do not assume. The model code exemption usually covers only small, low, freestanding decks that do not serve an exit door, and many jurisdictions change those terms. Your local building department can confirm in a short phone call.
Should I plan the framing or leave it to the contractor?
It helps to sketch it yourself even if a contractor builds it. Knowing the joist size, spacing and footing count lets you compare quotes on equal terms and spot a bid that is cutting corners. The contractor or your building department may still adjust the design to meet local requirements.