Building your own terrace: what's realistic to DIY

What to assess about the area and ground before you start

Before buying a single board, walk the site properly. Check the slope of the ground away from the house — you want a gentle fall away from the building, not towards it, otherwise you're building a terrace that channels rainwater straight at your foundation. A spirit level on a long straight batten across the area gives you a rough reading of how uneven things really are.

Dig a test hole or two to see what you're dealing with underneath. Estonian gardens vary enormously: sandy free-draining soil in some areas, heavy clay that holds water in others, and construction rubble left over from the original build almost everywhere. Clay soil that stays wet is the main reason posts heave in winter, so it changes how you plan the foundation.

If the terrace will sit against the house, check the level of the damp-proof course or the base of the cladding. The finished deck surface should sit below it, not level with it, so that rain splashing off the boards doesn't run into the wall.

Post layout and the depth frost won't be able to move

Mark out the post positions with string lines and a builder's square, checking corners are actually square by measuring the diagonals rather than trusting the eye. Post spacing typically runs 1.2 to 1.8 metres depending on what's carrying the load above, closer together if the terrace will take furniture, a hot tub, or heavy footfall.

The depth that matters is the frost depth for your area, not a number that feels sensible. In Estonia this generally means posts need to sit well below where the ground freezes and heaves in winter — shallow posts are the single most common reason a terrace starts rocking or tilting after its first winter. Ground conditions vary by plot, so if you're not certain, checking with the building register or a local contractor before you dig is worth the hour it takes.

Concrete the posts in, or use ground screws if the soil allows it, and let concrete cure fully before you load anything onto the posts. Rushing this step is invisible until the following spring, when it becomes very visible.

Joist spacing and material choices before the boards go down

Joist spacing depends on the decking board thickness and the direction you're laying them. As a rule of thumb, 45 centimetres between joist centres suits most standard boards; go tighter, around 30 centimetres, if boards will run diagonally or if you're using thinner composite decking, since composite needs more support than timber of the same size.

Pressure-treated pine is the usual choice for the frame because it's affordable and holds up outdoors, but check the treatment class matches ground contact or above-ground use as appropriate — they're not interchangeable. Thermally modified timber or composite boards cost more but move less with moisture, which matters on a frame that will see Estonian winters and wet fluctuating springs.

Fit noggins or blocking where boards will butt together end to end, and make sure every joist end is supported rather than cantilevered out past the last post. An unsupported joist end is where bounce and eventual sag start.

Fixing the boards and the gap water needs to get away

Leave a consistent gap between boards, typically 3 to 5 millimetres for timber and slightly less for composite, using scrap spacers as you go rather than judging by eye. This gap isn't cosmetic — it lets rainwater drain through instead of sitting on the surface, and it gives the timber room to expand when it's wet.

Screw rather than nail decking boards, with stainless or coated decking screws that won't streak the timber with rust over time. Pre-drill near board ends to stop splitting, and keep screw lines straight by snapping a chalk line across the joists before you start.

Leave a small gap where the decking meets the house wall too, not just between boards. Boards fixed hard against the wall trap moisture against the cladding and are one of the more common causes of rot showing up a couple of years later.

• Mark out and check diagonals before digging a single hole
• Set posts below frost depth, not to a guessed number
• Space joists to suit board thickness and direction
• Leave 3–5 mm between boards and a gap at the house wall
• Support every joist end; don't cantilever past the last post

Where most self-builders actually go wrong

The mistake we see most often isn't the boards, it's what's underneath them: posts set too shallow, or set into ground that was never properly checked for drainage. The deck looks perfect for a season and then one corner starts to lift or lean once the ground has been through a full freeze-thaw cycle.

The second most common issue is skipping the drainage gap, either between boards or against the house, because a tight fit looks tidier on the day. It's the kind of mistake that's completely invisible until the rot or the damp patch shows up, by which point boards usually need lifting to fix it properly.

When it's worth calling someone in

A straightforward ground-level terrace on decent, well-drained soil is a realistic weekend-and-a-bit project for someone comfortable with a spirit level, a post hole borer, and a saw. Where it stops being a DIY job is uneven or clay-heavy ground, a terrace attached to the house that has to work around the damp-proof course, or any structure raised enough that a mistake in the frame becomes a safety issue rather than a cosmetic one.

If the ground assessment or post depth has you guessing rather than measuring, that's the point to stop and get an opinion before concrete goes in, since it's far cheaper to fix on paper than to dig out. We build decking and terraces from 90 € per job once we've seen photos or a description, and if what you actually need first is a boundary fence sorted before the terrace goes in, fence repair and installation runs from 45 € per hour.