Construction of a substructure for decking


Not only for the load-bearing capacity, but also for the durability of a wooden terrace made of decking boards, the selection of the right wood and, above all, the correct processing in the substructure is decisive. Find out what to look for in the substructure of your terrace here.

Background information

Every planked wooden terrace needs a corresponding substructure. It is usually made of wood and laid as a stable structure.

Here, on the one hand, the type of wood used is decisive, but also the correct construction method. Otherwise, the load-bearing capacity of the terrace will not be properly ensured, or the substructure may rot prematurely or be attacked by pests, despite fundamentally weatherproof wood.

The right kind of wood for the substructure

Wood is divided into so-called hazard classes, which also state the degree of its resistance to weathering and pests. For the construction of the substructure wood of hazard class 3 or 4 should be used if possible.

These include not only tropical woods such as teak or bangkirai, which are naturally very weather- and pest-resistant, but also some native wood species such as Douglas fir or larch. For durability, the resin content is crucial. The so-called sapwood should not be used on all types of wood, as it is very susceptible to moisture. Among the untreated woods, Douglas fir offers by far the best value for money.

Proper construction

You should definitely avoid the direct contact between wood and earth when constructing the substructure - this is practically a guarantee for rapid decay. Also, the direct contact of two woods should be avoided as far as possible, since waterlogging can occur here. But that's not always avoidable.

The wood of the substructure should not come directly to the masonry but be separated by a bitumen layer of this. This also extends the life of the terrace already fundamentally.

Step-by-step instructions for a substructure on a plastic base

  • Squared timbers for the substructure
  • Angular and longitudinal connectors
  • screw
  • Anchoring material for substructure
  • Plastic base
  • Cordless Screwdriver
  • tape measure
  • spirit level
  • suitable saw for the squared timbers
  • Calculator and graph paper for planning

1. Construction planning

Before the execution is in any case an exact plan necessary. First, find out in what dimensions you can get squared lumber as free of splinters as possible - Douglas fir is very cheap in many saw mills and especially in large sizes up to six meters.

First of all, check again how strong your subfloor is and, if necessary, create a higher load capacity through a compacted gravel bed or a thin layer of concrete.

Then draw an exact plan for the substructure and calculate the required lengths and the total consumption of square timber for the substructure.

2nd cut

According to your design plan, first cut the side members of your structure exactly, then the cross connectors. Depending on the design, mitres may also be necessary.

3. Assembly of the substructure

Place the side rails at the planned distance and screw the cross connectors of your structure with angle connectors and, if necessary, longitudinal connectors. Work here as accurately as possible.

When the construction is finished, check the entire construction with the spirit level and align again exactly. Then attach the plastic sockets to the structure and adjust the height so that there is an approx. One to two percent incline - ie one to two centimeters difference in height per meter width.

4. Attach the construction

Depending on where exactly you build your terrace, you then have to attach the substructure to the house wall. Apply a watertight release layer, such as a bituminous paint, to the attachment site beforehand.

You do not necessarily have to fix the plastic bases - the weight of the wooden construction makes the terrace stand that stable.

Tips & Tricks

If you do not like the slightly "floating" feeling that the plastic bases lend to the patio, you can alternatively use concrete pedestals. These are not always easy to get and need to be attached.


Video Board: How To Build A Deck | #2 Framing [Beam/Joists/Ledger]