How to build decking steps

Inspired by a Skill Builder guide. This walk-through draws on the popular UK trade video “Building Decking Steps - What You Need To Know” from Skill Builder, Roger Bisby’s long-running UK building and trade channel. Worth watching before you pick up the circular saw - the bit on stringer layout alone will save you a head-scratch or two.

1. Measure the total rise and plan the steps

The total rise is the vertical distance from the deck surface down to the ground. Measure it carefully. Then divide it into equal risers - anywhere between 150 mm and 200 mm works well for outdoor steps. 175 mm is a comfortable middle ground.

Aim for a going (the horizontal depth of each tread) of at least 250 mm - 300 mm is better. The old rule of “two risers plus one going equals 600–650 mm” gives a comfortable stride. Do not make the steps too shallow or too steep to save on materials; you will regret both extremes.

2. Mark and cut the stringers

Stringers are the angled side pieces the treads sit on. Use a framing square or a stair square to mark out the riser and tread dimensions on a length of 47 × 150 mm or 47 × 200 mm pressure-treated C24 timber. Mark both notches all the way along before you cut anything.

Cut the notches with a circular saw, stopping just before the corner, then finish with a hand saw or jigsaw. Overcutting the corners weakens the stringer and can cause cracking over time. You need two stringers, one for each side. Cut the second from the first as a template to keep them identical.

3. Fix the stringers in position

The top of the stringers fixes back to the deck frame or a ledger board. The bottom sits on a hard surface - a concrete pad, a couple of paving slabs, or compacted hardcore. Keep timber off bare soil; it will rot far sooner than it should.

Use joist hanger connectors or angle brackets at the top. At the bottom, either bolt the stringers to a treated sole plate or use post-base clips. Everything should be galvanised or stainless steel - plated screws corrode quickly outdoors and can stain the timber.

4. Fit the treads

Use the same decking boards you used on the main deck if you have them, or match the thickness and profile. Standard 32 mm or 38 mm grooved decking board is fine. Each tread should overhang the front of the riser by around 20–25 mm for a clean look.

Fix each tread with two stainless steel screws per stringer crossing. Pre-drill to avoid splitting, particularly near the ends. Leave a small gap - around 5 mm - between boards if you are using two boards per tread, for drainage.

5. Add risers if needed

Open-riser steps (no board at the back) look fine and drain well, but if the deck is more than two steps high or children will use it regularly, closed risers are safer. Use a thinner board - 19 mm faced board or leftover decking - fitted vertically between tread and tread.

Risers also stiffen the whole staircase noticeably, which matters on longer runs. On short two-step runs off a low deck, risers are mostly cosmetic.

6. Fit a handrail if the height warrants it

Building Regulations require a handrail if there are more than two risers, or if the total rise is over 600 mm. Even for lower decks, a rail is worth adding if older family members will use the steps regularly.

The simplest approach is a post at each side bolted through the stringer, with a 90 × 90 mm newel top and a 44 × 44 mm handrail. Keep the top of the rail between 900 mm and 1,000 mm above the pitch line of the steps.

7. Treat and protect the timber

Apply a good-quality decking oil or preservative to all the cut ends first, then to the whole staircase once everything is assembled. Cut ends are by far the most vulnerable part - a coat of end-grain preservative before the tread goes on is good practice.

Plan to re-treat the steps annually or at least every other year. Steps take more foot traffic than the deck itself, so they wear quicker. A jet wash and a fresh coat of oil in spring keeps them looking right and extends their life considerably.

When to call a handyman

Call Richard if the deck is raised more than 300 mm off the ground, if you need balustrades to meet Building Regulations, or if you are not comfortable with the stringer cuts. Getting the geometry wrong means an uneven staircase that never feels quite right underfoot - worth doing properly from the start.