Decking looks straightforward until you actually build it. Then you realise there are about fifty ways to get it wrong, and most people manage to hit at least three or four of them. Here are the mistakes we see repeatedly, and how to avoid them.
Getting the Frame Spacing Wrong
This is probably the most common problem. People space joists too far apart because they’re trying to save money on timber, then wonder why the deck feels bouncy or the boards start sagging.
Standard deck boards need joist centres at 400-450mm maximum. Go wider than that and you’ll feel the boards flexing underfoot. It might not seem like much when you first build it, but give it a year or two and the bounce gets worse as the timber settles.
Composite decking often needs even closer spacing – check the manufacturer’s specifications because some require 300mm centres. Ignore this and you’ll void any warranty when problems appear.
The edges need proper support too. Nothing looks worse than deck boards overhanging unsupported at the sides, drooping down after a few months of weather.
Drainage That Doesn’t Work
Water needs somewhere to go. Build a deck that traps water underneath and you’re basically creating a rot factory.
The frame needs to slope slightly – even just 1 in 80 makes a difference. If you build dead level, water pools under the boards and takes forever to dry out. The timber stays damp, moss starts growing, and everything rots faster than it should.
Board spacing matters too. Fit them too tight and water can’t drain between the gaps. You need 5-8mm gaps to let water through. Some people worry this looks messy or that things will fall through the gaps, but proper spacing actually extends the life of your deck significantly.
Make sure water can escape from underneath the deck too. If you’re building on soil, the ground needs to drain. If it doesn’t, you’ll end up with standing water under your deck all winter.
Board Orientation Nobody Thinks About
Timber boards have a bark side and a heart side. Fit them bark side up and they cup upwards as they dry, creating channels that help water run off. Fit them heart side up and they cup downwards, forming little troughs that hold water.
Most people don’t even look at which way up they’re fitting boards. Then they wonder why some boards hold puddles whilst others shed water properly.
Check the end grain – the growth rings curve one way or the other. You want that curve facing up like a smile, not down like a frown.
Fixings That Give Up
Deck screws need to be properly galvanised or stainless steel. Standard interior screws rust out within a couple of years. You won’t notice until you step on a board and it moves because half the screws holding it down have corroded away.
Cheap deck screws strip easily when you’re driving them in, especially through hardwood. You end up with screws that aren’t fully tightened, and they work loose as the deck gets used.
Pre-drilling pilot holes takes longer but stops boards from splitting and makes screws go in properly. Skip this step and you’ll crack boards, especially near the ends.
Hidden fixing systems look tidier but they need installing correctly. If you don’t get them lined up right, boards move and the clips fail.
Maintenance Nobody Does
Treating your deck isn’t optional. Pressure-treated timber comes pre-treated against rot, but the surface still needs protecting once it’s exposed to weather.
Most people build a deck, use it for a year, then forget about it. Two years later the surface is grey, splintery, and starting to crack. Annual treatment with oil or preservative keeps timber in decent condition. Skip this and you’ll be replacing boards within five years instead of fifteen.
Clearing debris matters too. Leaves and dirt build up between boards, stay damp, and rot the timber from underneath. A quick sweep every few weeks stops this happening.
Planning Permission People Ignore
Most decking doesn’t need planning permission, but there are exceptions. If your deck’s over 300mm high, it might need building regulations approval. If it overlooks neighbouring properties or you’re in a conservation area, rules get stricter.
People build decking right up to their boundary fence without checking. If that deck’s raised and overlooks next door’s garden, you might have to take it down if they complain.
Check with your local planning authority before you start, especially if the deck’s going to be substantial or close to boundaries. It takes ten minutes and saves potentially expensive problems later.
Getting It Right First Time
None of these mistakes are difficult to avoid once you know about them. Take time to build the frame properly, space everything correctly, use decent fixings, and maintain the deck once it’s finished.
Rush the job or cut corners on materials and you’ll end up fixing problems within a couple of years. Do it properly from the start and your deck should last twenty years or more without major issues.