What You Need Before You Start Building

A deck is a platform attached to or freestanding from your house, built on posts set into the ground. Before you cut a single board, you need three things: a plan that shows dimensions and post locations, a building permit from your local code office, and an inspection schedule so the inspector can sign off at key stages. Most jurisdictions require permits for decks, and skipping this step can cost you when you sell the house or file an insurance claim.

Start by visiting your city or county building department in person or online. Tell them the deck size, height, and whether it will be attached to the house. They will give you the specific code requirements for your area — these vary by region and cover post depth, railing height, joist spacing, and snow load capacity. Some departments provide a standard deck plan you can use; others require a licensed designer. The permit fee typically ranges from $50 to $300 depending on deck size, but this varies widely by location.

Once you have the permit, you can order materials and schedule your first inspection. Most inspectors want to see the posts and footings before you build the deck frame, and again after the frame is complete but before you add the surface boards. Knowing the inspection schedule upfront keeps you from building ahead of the inspector's availability.

Key Takeaways

  • You must obtain a building permit from your local code office before construction begins, and the inspector must sign off at the post stage and again after the frame is complete.
  • Posts must sit on footings that go below the frost line in your area — typically 36 to 48 inches deep in cold climates — to prevent frost heave from pushing the deck up in winter.
  • The deck frame consists of a ledger board bolted to the house, a rim joist around the perimeter, and joists spaced 16 inches apart, all fastened with galvanized or stainless steel hardware.
  • Deck boards are typically 5/4 inch pressure-treated lumber or composite material, laid perpendicular to the joists with a small gap between each board to allow for water drainage and wood movement.
  • Railings must be at least 36 inches high and meet local code for baluster spacing, usually 4 inches or less, to prevent a child's head from passing through.

Digging Footings Below the Frost Line

The foundation of your deck is the footings — holes dug deep enough that frost cannot heave the posts upward in winter. The depth you need depends on where you live. In the northern United States and Canada, the frost line can be 48 inches or deeper; in the South, it may be 12 to 24 inches. Call your building department or check their website for the frost line depth in your area, because building on a shallow footing in a cold climate will cause the deck to shift and crack within a few years.

Dig a hole at each post location, going at least 6 inches below the frost line. Place a concrete footer tube (a cardboard cylinder sold at building supply stores) in the hole so the top sits 2 to 4 inches above ground. Pour concrete into the tube and set a post base — a metal bracket that bolts to the concrete — while the concrete is still wet. Let the concrete cure for 48 hours before you set the post on the base. If you are building on a slope, the posts on the downhill side will need deeper footings to keep them level.

For a freestanding deck not attached to the house, all posts sit on footings. For a deck attached to the house, the ledger board (the board bolted to the house) carries half the load, so the outer posts can sometimes be spaced farther apart. Your permit plan will show you exactly where each post goes.

Installing the Ledger Board and Framing the Deck

If your deck is attached to the house, the ledger board is the first piece you install. This board bolts directly to the house rim joist or band board — the horizontal board that runs around the perimeter of the house foundation. Remove any siding where the ledger will sit, bolt the ledger to the house with galvanized bolts spaced 16 inches apart, and seal the gap behind the ledger with flashing (a metal or rubber strip that sheds water). A leaking ledger connection is the most common cause of deck rot and house damage, so this step matters more than it looks.

Once the ledger is bolted down, install the rim joist around the perimeter of the deck, connecting it to the ledger at the house and to the outer posts at the corners. Then install the joists — the boards that run perpendicular to the rim joist and support the deck boards. Space the joists 16 inches apart (measured from the center of one joist to the center of the next), and fasten them with galvanized joist hangers or by toe-nailing with galvanized nails. All fasteners must be galvanized or stainless steel; regular steel will rust and stain the wood.

Before you install the deck boards, have the inspector sign off on the frame. At this point, the deck is just the skeleton — posts, footings, ledger, rim joist, and joists. The inspector will check that posts are plumb (perfectly vertical), that the frame is level, and that all fasteners are the right type and spacing.

Choosing and Installing Deck Boards

Deck boards are the surface you walk on. The two main options are pressure-treated lumber and composite material. Pressure-treated lumber is cheaper, typically $1 to $3 per linear foot, and is the most common choice. It is softwood (usually pine or fir) treated with chemicals to resist rot and insects. Composite decking is made from wood fibers and plastic, costs $3 to $8 per linear foot, requires less maintenance, and resists staining and fading, but is heavier and more expensive upfront.

Lay the boards perpendicular to the joists, starting at one end of the deck and working toward the other. Leave a gap of 1/8 inch to 1/4 inch between each board to allow water to drain and the wood to expand and contract with humidity changes. Fasten each board with two galvanized deck screws per joist, driven at a slight angle so they pull the board tight. Do not use nails; they work loose over time. If you are using composite boards, follow the manufacturer's instructions for fastening and spacing, as these vary by product.

Trim the edges of the deck boards flush with the rim joist using a circular saw or hand saw. If the deck is elevated more than 30 inches above the ground, you will need to install a railing before you can use the deck.

Building a Code-Compliant Railing

A railing is required on any deck higher than 30 inches above the ground. The railing must be at least 36 inches tall (measured from the deck surface to the top of the railing), and the balusters (the vertical pieces) must be spaced no more than 4 inches apart. This spacing rule exists so a child's head cannot pass through. Some jurisdictions also require the railing to withstand a horizontal force of 200 pounds applied to the top rail without moving more than 1 inch.

The simplest railing is a 2x4 top rail bolted to 4x4 posts at the corners and midpoints of the deck perimeter, with 2x2 balusters fastened between the top and bottom rails. Space the balusters 4 inches apart (measure the gap, not the center-to-center distance). Fasten everything with galvanized bolts or screws. If you prefer a different style — horizontal cables, glass panels, or composite balusters — check your local code first, because some styles have additional requirements.

After the railing is installed, the inspector will return for a final walkthrough. They will check the railing height, baluster spacing, and the overall structure. Once they sign off, the deck is complete and ready to use.

Common Mistakes That Lead to Deck Failure

The most frequent problem is a ledger board installed without flashing or bolted to the wrong part of the house. If the ledger is bolted to the rim board but water gets behind it, the rim board rots from the inside out, and the damage spreads into the house framing. This can cost thousands to repair. Always install flashing, and always bolt to the rim joist or band board, not to the siding or the brick veneer.

The second common mistake is shallow footings. Posts set on concrete pads sitting on top of the ground will heave upward in winter, cracking the deck frame and pulling the ledger away from the house. Frost heave happens gradually over several winters, so the damage is not obvious until the deck is already damaged. Dig below the frost line, every time.

The third mistake is using regular steel fasteners instead of galvanized or stainless steel. Regular nails and bolts rust within a year or two, staining the wood and weakening the connections. Galvanized fasteners cost a little more but last the life of the deck.

When to Call a Professional

If your deck is more than 12 feet wide, more than 20 feet long, or higher than 4 feet above the ground, consider hiring a contractor or a structural engineer to review your plan. Large decks and high decks carry more load and have stricter code requirements. A professional can also handle complex situations like building on a steep slope, attaching to a house with unusual framing, or designing a multi-level deck.

You can do the digging, framing, and board installation yourself if you are comfortable with a drill, a saw, and a level. The ledger board connection is the most critical step and the easiest to get wrong, so if you are unsure about flashing or bolting, hire someone for that part. The inspector will catch mistakes, but it is cheaper and faster to get it right the first time.

Frequently Asked Questions

Do I really need a permit for a small deck?

Yes. Most jurisdictions require a permit for any deck, regardless of size. A permit is inexpensive and protects you when you sell the house or file an insurance claim. If you build without a permit and the house inspector finds it during a sale, the buyer can demand you remove it or reduce the price. Some insurance companies will not cover damage to an unpermitted deck.

What is the difference between pressure-treated and composite decking?

Pressure-treated lumber is cheaper and easier to work with, but it needs staining or sealing every few years and can splinter. Composite material is more expensive upfront, requires almost no maintenance, and resists staining and fading, but it is heavier, can feel soft underfoot, and may discolor in direct sunlight. Choose based on your budget and how much maintenance you want to do.

Can I attach a deck to a mobile home or a house with vinyl siding?

You can attach to a mobile home if the manufacturer approves it and the home has a rim board strong enough to bolt to. You cannot bolt a ledger directly to vinyl siding; you must remove the siding and bolt to the rim board underneath. If the house has brick veneer, you must bolt to the rim board behind the brick, not to the brick itself.

How often do I need to stain or seal my deck?

Pressure-treated wood should be sealed or stained every two to three years, depending on weather and sun exposure. Composite decking rarely needs sealing, though some manufacturers recommend a light cleaning once a year. Check the product instructions for your specific material.

What should I do if the deck inspector fails my inspection?

The inspector will tell you what does not meet code. Common failures are posts not plumb, joists spaced incorrectly, fasteners missing or the wrong type, or the ledger not properly flashed. Fix the specific items the inspector noted and call for a re-inspection. Most inspectors will return within a few days at no extra charge.