Inspired by a helpful UK video. This guide draws on the practical "Replacing rotten timber decking boards" video, filmed by a DIYer in the North East of England. It's a clear, unsponsored walkthrough of removing old boards and getting the new ones fixed correctly - including what to do when the screws are completely buried in rot and won't budge.
1. Identify which boards need replacing
Walk the deck slowly and press your foot down on each board. Soft spots, springiness, or boards that flex under your weight are the obvious signs. Discolouration - dark grey or black patches - points to moisture sitting in the timber.
Poke suspected boards with a screwdriver. If the tip pushes in easily, the fibres have broken down and the board needs to come out. Sound timber will push back.
2. Remove the fixings and lift the boards
Most decking screws will be countersunk into the board face. If they're badly corroded, use a screw extractor bit or try cutting a new slot across the head with an oscillating multi-tool. Avoid brute-forcing them - you'll snap the screw into the joist below.
Badly rotted boards will sometimes snap or crumble as you lift. That's fine. Work in sections and clear the debris as you go so you can see what's underneath.
3. Check the joists while you're in there
This is the step most people skip and later regret. Poke every joist you can reach. Pay particular attention to where the joists sit on the posts or bearers - that's where water pools and rot starts.
Minor surface checking on a joist is not a crisis. Soft, punky wood that gives way easily is. If a joist is gone, that section of the deck needs a new joist before new boards go down. Fitting new boards over a rotten joist just delays the same problem by a couple of years.
4. Treat the joists and any new timber
Brush end-grain preservative onto any exposed joist cuts. Timber end-grain is where water gets in fastest, and a coat of Cuprinol or similar makes a real difference to how long things last.
New decking boards should ideally be treated or pressure-impregnated timber. Match the width and thickness to the existing boards - typically 120mm or 145mm wide and 28mm thick for residential decks. Cut lengths to overhang joists at either end by no more than 50mm.
5. Fix the new boards
Use stainless steel or hot-dip galvanised decking screws - at least 4mm x 65mm, countersunk. Two screws per board per joist, set 15–20mm from the board edge to avoid splitting. Pre-drill hardwood boards first.
Leave a 5–6mm gap between boards for drainage and expansion. A piece of 6mm ply offcut makes a handy spacer. New boards sitting tight against old ones will buckle within a season as the timber moves.
6. Stain or treat the new boards to match
New timber is noticeably lighter than weathered boards. Apply two coats of a decking stain or oil that matches as closely as possible, then treat the whole deck to blend everything in. The colour will even out over a season or two, but treating helps it along.
To be fair, a perfect colour match on day one is almost impossible. New wood is just a different colour. The gap closes faster than you'd think once both sets of boards have had some sun and rain.
When to call a handyman
Call Richard if more than a third of the boards need replacing, if any of the main joists or posts are rotted through, or if the deck is elevated and the structural work is beyond straightforward. A few boards is a satisfying afternoon job. Rebuilding the subframe is a different kind of job entirely.
Decking repairs in Sandwich and Kent?
The Sandwich Handyman can assess your deck, replace individual boards, treat the structure, and get things looking right again without tearing out the whole thing unnecessarily.
Contact Richard