When is the best time to build a terrace?

Many homeowners choose to build a terrace in spring, when temperatures rise and daylight hours increase. However, if you plan to work with professional contractors, autumn can be a good alternative as tradespeople are often less busy.

Before starting, it is advisable to estimate material and labour costs in advance. If you plan to build the terrace yourself later in the year, keep in mind that weather conditions may delay the work.

Preparation before construction

A garden terrace should ideally connect directly to the house, usually via patio or back doors. It is recommended that the terrace surface sits around 6 to 7 centimetres below the internal floor level to help prevent moisture issues.

The ground must be level and free from roots, stones and other obstructions. If you intend to install outdoor lighting or electrical sockets, the necessary cabling should be planned and installed before construction begins.

Mark out the terrace area according to the planned dimensions and allow extra space around it for comfortable working and access.

1. Measuring and cutting the wall ledger board

Using a spirit level and pencil, mark the position of the ledger board on the external wall of the house. This board will support the main joists of the terrace. Carefully cut away the exterior cladding along the marked line. Any areas that cannot be reached with a saw can be finished using a chisel and hammer.

2. Fixing the ledger board to the wall

Install a metal flashing above the cut section to protect the structure from moisture. Secure the ledger board firmly to the load bearing wall using suitable fixings. Seal all fixings and joints with an exterior grade sealant to prevent water ingress.

3. Marking the positions of the support posts

Measure approximately 2.5 metres out from the ledger board into the garden and mark the locations for the foundation posts. Use string lines and a plumb line to ensure accurate alignment and positioning.

4. Digging and pouring the foundations

Excavate holes for the foundations to a depth suitable for local ground conditions and frost protection. Add a layer of gravel around 7.5 centimetres deep to the bottom of each hole.

Insert concrete form tubes and fill them with concrete. While the concrete is still wet, install anchor bolts or post supports that will later hold the timber posts securely in place.

5. Installing the posts

Attach metal post bases to the anchors and secure them firmly. Cut the timber posts to the required height, position them in the bases and check that they are perfectly vertical before tightening all fixings.

6. Installing the main beam

Fix the main support beam on top of the posts. Use metal connectors and galvanised screws to ensure a strong and durable connection. This beam plays a key role in the overall stability of the terrace.

7. Assembling the frame

Install the outer beams and connect them to the main beam to form the terrace frame. The structure should form a clean rectangle. Measure the diagonals to confirm that the frame is square.

8. Installing the joists

Mark joist positions at approximately 40 centimetre intervals along the ledger board and main beam. Fix joist hangers in place and install the joists securely.

9. Laying the decking boards

Lay the decking boards loosely at first to check spacing and alignment. Leave a gap of around 3 millimetres between boards to allow for natural expansion. Secure the boards with suitable screws, working from the house outwards.

10. Steps and railing

If the terrace is raised above ground level, steps will be required for safe access. For higher terraces, installing a railing is strongly recommended. All dimensions and safety features should comply with current building regulations.