How Much Does It Cost to Repair or Replace Rotten Decking Boards?

Replacing a handful of rotten timber decking boards typically costs £150-£400 including labour and materials for a small area, while replacing an entire deck's boards (keeping the existing substructure) commonly runs £1,500-£4,000+ depending on size — the right choice depends on how widespread the rot is and, critically, whether the substructure underneath is still sound.

Repairing individual boards

If only one or a few boards show rot, cracking or soft spots while the rest of the deck (and the joists beneath) remain solid, targeted board replacement is usually the sensible, cost-effective option.

• Typical cost: roughly £30-£60 per board including materials and labour for straightforward access, more if boards are in an awkward spot or need cutting to match an existing pattern.
• DIY or professional: replacing a single accessible board is a realistic DIY job for someone comfortable with basic tools — see our guide to board spacing and joist centres for how boards are typically fixed, which affects how straightforward removal and replacement will be.

When to consider full board replacement

If rot is scattered across many boards, or concentrated in a way that suggests a systemic issue (poor drainage, inadequate ventilation, consistently damp ground), replacing all the boards while keeping a sound substructure is often more cost-effective than repeated one-off repairs — and gives you a uniform, matching finish rather than a patchwork of old and new boards weathering at different rates.

When the substructure itself needs replacing

This is the more expensive scenario, and the one worth checking for carefully before committing to "just" replacing the visible boards. Signs the substructure (joists, posts, bearers) has failed include: significant give or bounce when walking on the deck, visible rot or soft, spongy timber when probed with a screwdriver, or boards that have sunk or gone uneven despite looking fine individually.

• Typical cost: a full rebuild including substructure commonly runs £100-£200+ per square metre, broadly comparable to installing a new deck from scratch, since much of the labour (excavation, base preparation, structural framing) is the same regardless of whether old decking existed before.
• It's rarely worth putting new boards on top of a compromised frame — you'll likely be paying for the same job again within a few years once the underlying rot progresses further.

What causes decking boards to rot?

• Poor drainage or ventilation underneath — moisture trapped against the underside of boards and joists is the most common cause, particularly on ground-level decks built too close to soil without an adequate air gap.
• Neglected maintenance — see our decking maintenance guide for the cleaning and re-oiling routine that meaningfully slows this process on timber decking.
• Standing water from poor slope/fall in the original construction, allowing water to pool rather than drain away.
• Untreated or poor-quality timber used in the original build, or timber where the factory treatment has been compromised by cutting exposed, untreated ends without resealing.

Should you switch to composite when replacing boards?

If you're already replacing most or all of a timber deck's boards, it's worth genuinely considering composite as an alternative rather than automatically replacing like-for-like — see our comparison of composite vs timber decking costs. The higher upfront cost may be worth it if you'd rather not face this same repair decision again in another decade.

Common mistakes

• Screwing new boards straight onto a substructure without checking it's actually sound first.
• Ignoring early soft spots or discolouration, letting rot spread to previously healthy boards and joists nearby.
• Using the wrong grade of treated timber for ground-contact or high-moisture areas, which fails faster than correctly rated timber.

Getting a fair quote

Get at least two or three quotes for anything beyond a single-board DIY repair, and ask each tradesperson to specify clearly whether the price includes substructure inspection, not just visible board replacement — a quote that skips checking the joists can end up cheaper on paper but leave a real problem undiscovered. Be wary of a quote that's dramatically lower than others for the same described scope; it may signal shortcuts on treated timber grade or fixings that will cost more in the long run.

DIY vs hiring a professional

Replacing an individual, easily accessible board is a realistic DIY job for someone comfortable with basic tools and a bit of patience matching the existing finish. Assessing whether the substructure is sound, however, is worth a professional opinion if you're not confident distinguishing surface weathering from genuine structural rot — probing suspect timber with a screwdriver (does it push in easily, feel spongy, or crumble) is a useful first check, but a tradesperson's experienced eye will catch things an untrained inspection might miss, particularly with joists that look fine from below but are compromised where they meet fixings or posts.