A garden deck lasts 25 years or fails in five mainly because of three things: how well air circulates underneath, how the boards are fixed, and how dense the timber is. The look of the boards on day one tells you almost nothing about any of them. Most early failures trace back to a deck built flat against damp ground with too little airflow, or to boards that cup and split because the wrong timber met the wrong conditions. This guide explains where decks go wrong, how to choose boards that cope with British weather, and how to lay and look after them so the investment pays off.
Know the three ways a deck fails
Moisture is the root cause behind nearly every failed deck, and it shows up in three forms: standing water, trapped damp and corroding fixings.
Standing water. Boards laid with no fall, or with gaps too narrow to drain, hold water on the surface. That feeds algae, which makes the deck slippery, and lets water soak into end grain where rot starts first.
Trapped damp underneath. A deck sitting low on bare soil with blocked sides cannot dry out. The joists and the underside of the boards stay wet through winter, even when the top looks fine.
Failing fixings. Cheap zinc-plated screws rust, stain the boards around them and eventually lose their grip. In dense timber, screws driven without pilot holes also split the board ends.
None of these is a timber defect. They are build and material choices, which is why two decks built the same year can look very different a decade later.
Pick board material for the decade you want, not the first summer
Hardwood boards cost more per square metre than softwood or composite, but they take the least maintenance and tend to stay flat the longest. The dense grain resists rot and insects without a chemical treatment, so the deck keeps its strength even after the surface has weathered.
| Softwood (treated) | Composite | Hardwood | |
| Upfront cost | Lowest | Highest | Mid to high |
| Rot resistance | Depends on treatment depth | High, but not affected by timber decay | Naturally high |
| Surface upkeep | Regular staining or oiling | Occasional cleaning | Oiling optional to keep colour |
| Typical weathering | Greys, can cup and split | Fades slightly in the first year | Silvers evenly if left untreated |
| Slip risk when wet | Higher once algae builds up | Varies by profile | Lower with a reeded or grooved face |
Balau is a common hardwood choice for UK gardens because it is hard, tight-grained and holds up in damp conditions. If you want to compare what is available, look at hardwood decking boards, where a reeded and grooved profile gives extra grip underfoot, which helps on a deck that stays damp through the winter.
Whichever material you choose, buy a few boards more than the plan needs. Cut-offs, mistakes and a spare for future repairs usually add up to about 10 percent.
Build the frame so air can move underneath
A ventilated, well-supported frame matters more than the boards on top. A void of at least 150mm between the ground and the underside of the joists, open on at least two sides, lets the structure dry out after rain.
Start by clearing and levelling the ground, then lay a weed-suppressing membrane and cover it with gravel. Without this, weeds push up through the gaps and the soil stays damp beneath the deck.
Set joists at 400mm centres for most domestic decks, or 300mm if the boards are thin or the deck takes heavy loads such as a hot tub or large planters. Give the frame a slight fall of about 1 in 100 away from the house so water runs off rather than pooling.
Paint cut ends of joists with preservative and fit a damp-proof strip on top of each joist. The strip stops water lodging between joist and board, which is where decks tend to rot first.
Fix the boards with the right screws and gaps
Correct gaps and stainless fixings prevent most splitting, cupping and rust staining. Dense hardwood is harder to fix than softwood, so pilot holes are not optional.
- Let the boards acclimatise by stacking them flat in the garden, with spacers between, for a few days before laying.
- Start the first board along the edge, with the reeded or grooved face up, and overhang the frame by no more than 25mm.
- Pre-drill every screw hole, and countersink so the heads sit just below the surface.
- Use stainless steel decking screws, two per joist crossing, set about 15mm in from each board edge.
- Leave a gap of 5mm to 8mm between boards for drainage, and 3mm to 4mm at board ends.
- Check the line every few boards, and trim the last board to fit rather than forcing it.
Seal cut ends with end-grain sealer or oil as you go. Fresh cuts are the most absorbent part of any board, and a few minutes of sealing slows moisture getting in.
Clean twice a year and oil only if you want the colour
Sweeping and one proper wash each spring and autumn keeps most decks in good shape, because dirt and leaf litter hold the moisture that algae and rot need.
Sweep along the gaps with a stiff brush or a thin scraper to clear packed debris, then wash with a decking cleaner and a soft brush. A pressure washer on a low setting works on hardwood, but keep the nozzle moving and parallel to the grain so it does not raise the fibres.
Hardwood does not need oil to survive. Left alone, it weathers to a silver grey. If you prefer to keep the original warm tone, clean the surface, let it dry fully and apply a decking oil with UV protection, then repeat once a year or as the colour fades. Move planters now and then so the boards underneath do not stay wet or stain.
