What You Need to Do Before You Start Cutting

Replacing deck stairs means removing the old stringers (the angled boards that support the steps) and treads (the boards you step on), then installing new ones in their place. The job takes a weekend for most homeowners and requires basic carpentry tools—a circular saw, drill, level, and tape measure. You do not need to rebuild the entire deck, just the stair assembly.

Before you remove anything, measure the rise (vertical distance from the deck to the ground) and run (horizontal distance from the deck edge to where the stairs land). These two numbers determine the size and angle of your new stringers. A standard step is 7 to 8 inches tall and 10 to 11 inches deep. If your old stairs do not match these proportions, your new ones should—uneven steps are a fall hazard and building codes enforce this.

Check your local building code for stair requirements. Most jurisdictions require handrails if the stairs are more than three or four steps tall, and the handrail must be between 34 and 38 inches high. Some codes also specify the maximum gap between balusters (vertical posts) to prevent a child's head from getting stuck. Knowing these rules before you build saves you from tearing out work later.

Key Takeaways

  • Measure the total rise and run of your stairs before you buy materials, because these dimensions determine stringer angle and step height.
  • Remove the old stringers by unbolting them from the deck band board and cutting them free at the ground, then pry out the old treads.
  • Cut new stringers using a stair-gauge jig or a calculator to mark the step notches accurately, then test-fit one stringer before cutting the rest.
  • Attach stringers to the deck with bolts or lag screws rated for outdoor use, and find the bottom end to a concrete pad or gravel base.
  • Install treads with corrosion-resistant fasteners and leave a small gap between boards to allow water to drain and wood to expand.

Removing the Old Stringers and Treads

Start by unbolting the old stringers from the deck. Most stringers are fastened to the band board (the rim of the deck) with bolts or lag screws. Use a wrench or socket to remove these fasteners. If bolts are rusted, spray them with penetrating oil and wait 15 minutes before trying again. Do not force a stuck bolt—you risk stripping it or breaking the tool.

Once the top is free, cut the stringers at ground level with a reciprocating saw or circular saw. If the stringers are sitting on a concrete pad or gravel, you may be able to straightforward lift them out. If they are buried or set in concrete, you may need to dig around them first. Remove all the old treads by prying them up with a pry bar. Discard them or set them aside for scrap.

Inspect the band board where the stringers were attached. If it is rotted or soft, you will need to replace that section before installing new stairs. Press a screwdriver into the wood—if it sinks in easily, the wood is compromised. Rotted wood will not hold fasteners securely and the stairs will fail.

Calculating and Cutting New Stringers

Measure the total rise by measuring straight up from the ground (or the landing pad) to the top of the deck. Measure the total run by measuring horizontally from the deck edge to where the stairs will land. Divide the rise by the number of steps you want. For example, if the rise is 28 inches and you want four steps, each step is 7 inches tall.

Use a stair-gauge jig to mark the notches on your stringers. A stair gauge is a pair of adjustable stops that clamp onto a framing square and let you mark identical step notches quickly. Set one gauge to the rise (7 inches in the example above) and one to the run (10 inches). Place the square against the edge of a 2×12 board and slide it along, marking the notch outline each time. This method is faster and more accurate than measuring each notch by hand.

Cut the notches with a circular saw or jigsaw, staying on the waste side of the line. Do not cut past the corner of each notch—stop the saw and finish the corner with a handsaw or jigsaw to avoid weakening the stringer. After cutting, test-fit one stringer on the deck to make sure the steps are level and the angle feels right. Adjust if needed, then use that stringer as a template to mark and cut the others.

Installing the New Stringers

Position the stringers on the deck and drill pilot holes through the band board. Use galvanized or stainless steel bolts rated for outdoor use—regular steel bolts will rust and fail. Bolt diameter is typically 1/2 inch. Space bolts about 12 inches apart along the band board. Tighten bolts snugly but do not over-tighten, which can crack the wood.

At the bottom, the stringers need a solid base. If you have a concrete pad, bolt the stringers to it using concrete anchors. If you do not have a pad, dig out a shallow trench, lay down landscape fabric, and pour a 4-inch concrete pad. Let the concrete cure for 48 hours before installing the stringers. If you prefer not to pour concrete, you can set the stringers on gravel and find them with metal brackets bolted to the deck, but concrete is more stable and longer-lasting.

Check that the stringers are level side to side and that the steps are level front to back. Use a 4-foot level and adjust shims under the stringers if needed. The stringers should be parallel to each other and spaced so that treads will not sag in the middle. For stairs wider than 3 feet, use three stringers instead of two.

Installing Treads and Finishing

Cut treads from pressure-treated 2×10 or 2×12 boards. Each tread should overhang the stringer by about 1 inch on each side. Lay the first tread on the lowest notches and fasten it with corrosion-resistant screws or bolts—stainless steel or galvanized. Use at least two fasteners per stringer. Do not use nails; they work loose over time as the wood moves.

Leave a 1/4-inch gap between the tread and the stringer to allow water to drain and the wood to expand and contract with humidity. This gap also prevents water from pooling and rotting the wood. Install the remaining treads the same way, working your way up the stairs.

If your stairs are more than three or four steps tall, install a handrail. The handrail must be between 34 and 38 inches high, measured from the top of the tread. Balusters (vertical posts) must be spaced no more than 4 inches apart so a sphere 4 inches in diameter cannot pass through. Handrails and balusters are available as kits from home centers and can be bolted to the stringers.

Common Mistakes to Avoid

The most common error is cutting stringers with uneven step heights. This happens when you do not measure carefully or when you use a stringer from old stairs as a template. Uneven steps are dangerous and building inspectors will reject them. Always calculate step height mathematically and mark notches with a stair gauge.

Another mistake is fastening stringers with nails instead of bolts or lag screws. Nails loosen as the wood shrinks and swells, and the stairs will eventually wobble or separate from the deck. Use bolts rated for outdoor use and tighten them firmly.

Do not skip the concrete pad at the bottom of the stairs. Stringers sitting directly on soil or gravel will rot within a few years because water pools around the base. A concrete pad keeps the wood dry and the stairs stable. If you cannot pour concrete, at least create a gravel base with landscape fabric underneath to improve drainage.

When to Call a Professional

If your deck is more than 4 feet high, if the rise or run is unusual, or if you are unsure about local building codes, hire a carpenter or contractor to design the stairs. A professional can also help if the band board is rotted or if the deck structure is not sound. Stairs that are built wrong are a serious safety hazard, and the cost of a professional design is worth the peace of mind.

If you do not own a circular saw or jigsaw, you can rent these tools from a home center for about $20 to $30 per day. Renting is cheaper than buying if you only need them for this project. Some home centers also offer free classes on how to use power tools safely.

Frequently Asked Questions

How long do deck stairs last before they need replacing?

Pressure-treated stairs typically last 15 to 20 years if they are maintained and kept dry. Cedar or composite stairs may last longer. The first parts to fail are usually the treads, which wear faster than the stringers. If only the treads are rotted, you can replace just those without replacing the stringers.

Can I use the old stringers if they are still solid?

Yes, if the stringers are not cracked, rotted, or warped, you can reuse them. Clean them, inspect them carefully, and install new treads on top. This is faster and cheaper than cutting new stringers. However, if the old stairs were uncomfortable or unsafe, new stringers with correct dimensions are worth the extra work.

What is the best material for deck stairs?

Pressure-treated lumber is the most affordable and widely available. Cedar is attractive but more expensive and requires regular sealing. Composite materials like Trex do not rot and require less maintenance, but they are the most costly option. For stringers, pressure-treated 2×12 is standard. For treads, any of these materials will work, depending on your budget and maintenance preference.

Do I need a permit to replace deck stairs?

Most jurisdictions require a permit for any structural work on a deck, including stair replacement. The permit process usually involves a plan review and a final inspection. Permits cost between $50 and $200 depending on your area. Check with your local building department before you start work. Working without a permit can result in fines and problems when you sell the house.

What if the ground is sloped and the stairs will not be level?

If the ground slopes, dig out the area under the stairs to create a level base, or pour a concrete pad that is level. Do not try to compensate by making the stringers uneven—this creates unsafe steps. A level base is essential for safe stairs, even if it means extra digging or concrete work.