The short answer
Most states and cities build their rules on the International Residential Code, the model code for houses. Its list of work that doesn't need a permit includes decks, but only when all four of these are true:
- The deck is 200 square feet or smaller.
- It's no more than 30 inches above the ground at any point.
- It's not attached to the house.
- It doesn't serve the required exit door of the house.
Miss any one of them and the model code wants a permit. A 12 × 16 deck is 192 square feet, so a low freestanding one can qualify. Bolt the same deck to the house and it no longer does.
That's the model code. Your state or city decides what actually applies where you live, and many change it. Check with the local building department before you buy lumber.
Why each condition is there
Size. A bigger deck holds more people, more furniture and sometimes a hot tub, so its footings and beams carry more.
Height. 30 inches is also the height at which the code requires a guard, the railing that stops people falling off the edge. Above it, a fall can do real harm, and the railing posts have to be fastened to the frame properly. The railing calculator prices one.
Attached to the house. A deck fastened to the house hangs from a ledger board bolted to the house framing. That connection is the one inspectors look at hardest. A ledger with the wrong fasteners can pull away under load, and a ledger without flashing lets water in behind it and rots the house itself.
The exit door. If the deck is the way out of the house, its stairs and landing are part of the escape route, so they have to meet the rules for stairs and exits. The stair calculator works out risers and treads within the code limits.
How cities change the rule
Local versions of the code differ, sometimes a lot. A few real examples:
- Austin, Texas, adds a fifth condition: the deck can't be in a flood hazard area.
- Utah drops the 200-square-foot limit and exempts low decks that don't need a guard.
- Federal Way, Washington, keeps the four conditions as the model code writes them.
Some places are stricter than the model code and ask for a permit on almost any deck. The only way to know is to ask your building department, most of which answer by phone or post the rule on their website.
What the permit process looks like
Plans
Expect to draw two things. A site plan shows where the deck sits on the lot and how far it is from the property lines. A framing plan shows the footing size and depth, the beam and joist sizes and spacing, how the ledger attaches, and the railing and stair details.
You don't have to invent the framing. The American Wood Council's DCA 6 guide gives span tables and connection details for ordinary wood decks, and some building departments hand out their own deck guide based on it.
Inspections
Usually there are three: the footing holes before the concrete goes in, the framing before the decking covers it, and a final once the railing and stairs are on. Don't pour or cover anything until the inspector has seen it.
Fees and timing
Fees vary widely. Many departments base them on the project's value or size and publish the schedule online. Review can take anything from a few days to several weeks, depending on the office and the time of year.
The other approvals
Zoning rules such as setbacks from the property line apply even to decks that don't need a building permit. If you're in a homeowners association, it may want to approve the plans too. And call 811 before you dig the footings: it's free, and it gets buried utility lines marked.
What can happen if you skip it
If an inspector notices the work, you can get a stop-work order or a fine, and be asked to open up finished work so it can be checked, or take it down.
The bigger cost often comes later. An unpermitted deck can come up when you sell the house, through the buyer's inspection or the county's records, and you may have to permit it after the fact, fix it or knock the price down. If someone is hurt on it, its history can come up in the insurance claim.
If you're hiring a contractor
In most places the contractor applies for the permit. Put that in the contract, and ask to see the permit before work starts. A contractor who suggests skipping it to save time is telling you something about how they build.
Fair questions
Do I need a permit to replace the deck boards?
Often not. Swapping boards on a sound frame is usually treated as a repair. Replacing joists, beams or posts, or adding stairs or a railing, can change that, so ask. The resurfacing calculator prices new boards on an existing frame.
What about a low, floating deck in the yard?
Under 30 inches, under 200 square feet and not touching the house is the textbook exempt deck in the model code. It still has to meet your zoning setbacks.
Does a permit make a deck safe?
It means someone checked the footings, the framing and the connections at the moments they were still visible. It isn't a warranty, but it catches the mistakes that matter most.
Sources
- International Residential Code, Section R105.2: the model list of work that needs no building permit, including fences up to 7 feet and small detached decks. States and cities adopt it with their own changes.
- Western Timber Frame, Deck permit requirements: the 2021 IRC deck exemption word for word, and examples of how Austin and Utah change it.
- City of Federal Way, Washington, Residential permit exemptions: an example of a city that adopts the IRC list with changes of its own, such as a 6-foot fence limit.
- International Residential Code: sections R312 (guards), R311.7.8 (handrails) and R507 (decks). Your city or state adopts and amends it, so check the local version.
- American Wood Council, DCA 6: Prescriptive Residential Wood Deck Construction Guide: ledger attachment, joist spans, guards and stairs for wood decks.
- Call 811: the national call-before-you-dig service, for when and how to have buried utilities marked.
