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A wooden terrace exudes warmth and invites you to a pleasant stay. For a permanent solution, however, it depends on the right substructure of the wooden terrace. Our instructions will help you step by step to the perfect assembly.

In a nutshell

  • a frost-proof layer of gravel keeps the terrace flat and straight even after years
  • instead of complex foundations, the substructure can be easily built on concrete slabs
  • a slight incline of the substructure of 1 to 2% safely drains rainwater away from the terrace

The structure

A wooden terrace differs fundamentally from other terraces with stone or tile coverings. In contrast to other types of construction, the visible surface is not the only "level" that also drains rainwater. Instead, another level is added under the substructure, which drains water, absorbs loads and, last but not least, provides the necessary rear ventilation to drain moisture and moisture from the sensitive wooden structure. A typical structure looks like this from top to bottom:

  • Wooden floorboards (placed at a distance because of shrinkage and swelling of the wood) - the actual floor covering
  • Substructure made of wood and aluminum - ensures distance to water and moisture and brings cohesion to the construction
  • Securing the position using paving slabs or similar (alternative: concrete foundations)
  • Base and infiltration layer made of water-bound mineral mixture

The material

If you start building your wooden terrace “from scratch”, however, you will need a number of building materials and tools for the substructure:

  • Split, crushed stone or mineral concrete
  • Weed fleece (permeable to water), ideally black
  • Concrete slabs, e.g. pavement slabs 30x30cm, at least 3 to 4 centimeters thick
  • Squared timber, at least 6x6cm, better 6×8 to 1x10cm, ideally the same material as the decking
  • alternatively: special aluminum profiles for terrace substructure
  • Screws, e.g. 6×140 with suitable dowels

The tool

With the right tool, the work is easy to do during this time:

  • Shovel, spade, pickaxe
  • vibrating plate
  • bucket, wheelbarrow
  • Ruler or straightedge
  • Guideline with ground needles
  • Meter rule, tape measure, laser spirit level
  • Drill with masonry drill bit and wood or metal drill bit
  • Circular or chop saw with wood or aluminum saw blade

The instructions - step by step

Now it's time to put your plan into practice using easy-to-understand steps:

Step 1 - Determine the top edge

In order for your terrace to be at the right height later on, you have to create the right heights for the substructure. Proceed in such a way that you determine the planned height of the floor covering, e.g. from the terrace door etc., and mark it on the house wall. Now count down:

  • Decking thickness
  • plus the thickness of the substructure
  • plus thickness of concrete slabs
  • = upper edge of the base course

Step 2 - Set the slope

Every terrace has a certain incline so that rainwater does not stand still but drains off quickly. A value of around 1 to 2 percent is usually chosen for this, i.e. one or two centimeters per meter length. The slope away from the house is typical, so that water never has the opportunity to penetrate the house wall or terrace door and possibly cause damage. On the other hand, the slope over the shorter side leads to a smaller height offset between the high and low points.
When creating the sub-base, first orientate yourself to the lowest point and measure it. To do this, add the height difference between the high and low points (distance x selected slope in centimeters) to the previous calculation of the construction height. Once a level surface has been created at this level, work out the slope in the direction of the high point by applying material and using the leveling batten to draw it towards the marked high point.

Step 3 - The Base Layer

Once the heights have been determined, create the supporting and water-draining layer for the substructure of your wooden terrace:

  • Outline terrace + stake out 60 centimeters on all sides
  • Cut and clear lawn
  • Excavate the subsoil to at least 60, preferably 80 centimeters below the surface of the ground, store the excavated material on the side or dispose of it
  • Fill the pit in layers of 20 centimeters with gravel, KFT or mineral concrete and compact
  • Level the upper edge of the supporting layer on the side by around 10 centimeters beyond the planned terrace, level the surface with a straightedge and a laser spirit level
  • then bend outwards 45 degrees downwards
  • Fill the remaining excavation above embankments with excavated earth, later cover with sod and press and water

Step 4 - The Intermediate Level

Regardless of whether you use squared timber for the substructure of your wooden terrace or aluminum profiles to hold the planks, it is very difficult to build them up securely on the gravel base layer. The use of foundations or other ground anchors would be possible. On the other hand, the use of concrete paving slabs is far simpler:

  • Determine the axes of the squared timber or aluminum profiles (carrying axes)
  • at right angles to the later floor covering
  • laterally indented about 20 centimeters from the board ends
  • between distances of 70 to a maximum of 75 centimeters
  • Lay out paving slabs evenly on the supporting layer in support axes
  • Distances in the direction of the axes by 1.00 meters each
  • Check the upper edges of the concrete slabs for evenness using a laser spirit level and straight edge
  • if necessary, align individual slabs with a rubber mallet and gravel
  • Cover the base layer with concrete slabs with weed fleece, overlap joints by 30 centimetres

Notice: The weed fleece is not absolutely necessary. However, it creates a uniformly dark look between the subsequent joints of your wooden deck.

Step 5 - The Support Profiles

The core element of the substructure of your wooden terrace is now the level that will accommodate the later floorboards - the squared timber or aluminum profiles.

  • Cut wood to terrace length
  • Align the squared timbers on the support axles and check the distances between them
  • Alignment: narrow side down / up, long side to the side (upright)
  • Drill holes in the wood above concrete slabs twice per slab, top to bottom
  • Transfer holes to concrete slabs
  • also drill through with a masonry drill and drive in dowels
  • Screw wood to concrete slabs to secure the position

Notice: Proceed in the same way with aluminum profiles as substructure. However, make sure to use suitable saw blades and drill bits.

Done, they did it. Now you can align and screw the wooden terrace of your choice directly to the created construction.

frequently asked Questions

Is an aluminum construction better than wood?

There is no real “better” when it comes to your terrace construction. Aluminum gets by with lower construction heights, but is somewhat more difficult to handle. Wood needs more space for the same load-bearing capacity, but it also forgives any inaccuracies in the preparation.

Is water a problem in terrace construction?

If your subsurface has the necessary incline and the squared timbers over the concrete slabs are not lying flat on a damp subsurface, water is not a real problem. Although your wood will become damp and swell a little, it will dry out quickly and shrink again. Sufficiently large joints are important in the later covering so that the swelling floorboards do not build up any tension.

What does a terrace structure on foundations look like?

If you want to base your wooden terrace on foundations, point foundations are made instead of the flat base layer. These then act like the concrete slabs and serve to hold the squared timber. Depending on the distance between the foundations, the timbers then have to be significantly larger. However, the effort involved with this method is considerably greater than with surface foundations.

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