Substructure terrace

Terrace substructure: Tips and ideas for the ideal terrace construction!

Reading time 9 minutes

Property owners with their own garden want a beautiful terrace. Many terraces have come of age, are too small for the desired uses, or are damaged. As a rule, it is not that difficult to build a modern and durable terrace with your own means. In this guide, you will find out what you should pay attention to with such a substructure for the terrace.

Very important: With a terrace, it always depends on the respective subsoil situations. A terrace substructure thus forms the basis for maximum stability and service life of your new terrace. Therefore, you should attach great importance to planning and preferably get professional support one time more than necessary.

Contents

• What should the terrace look like at the end?
• Important notes on the subsoil
• Terrace sub-base on grass/lawn/soil
• Terrace substructure on concrete
• Building up a flat-roof terrace correctly
• What to do with uneven ground?
• Calculations & spacing of the battens
• Construction battens made of wood
• Construction battens made of aluminum
• Construction battens made of WPC
• Adjustable pedestals for severe unevenness
• FAQ

Clarify the look right at the beginning: What should the terrace substructure look like at the end?

First, you should decide what the terrace should look like later on. As a rule, most people use wood or WPC panels for the top covering. These materials not only look good, but are also easy to maintain and clean. The panels are available in numerous colors, which you should ideally choose to match your garden or your house.

Finally, you have the option...

• to build a rectangular terrace
• to build a square terrace
• to build an angled terrace
• to build a rounded terrace

...to build one. Here, it depends on how it is supposed to fit into your garden.

If you want to build a patio roof later on, you should also consider the foundation for the load-bearing beams right away. Afterward, in that case, you would have to remove the top panels again and at the same time reinforce the substructure for the terrace at those points.

However, before you move on to the top, visible covering, you need a solid substructure for the terrace.

The following types of substructures for terraces are the most common:

• wood construction battens
• the aluminum substructures
• WPC construction battens

The different construction types will be discussed in a bit more detail later.

Important notes on the substructure base

With a substructure for the terrace, you should always take the subsoil into account, which should ideally offer high stability. In addition, the ground there is not always level, but can also contain depressions and inclines.

You usually see what this ground is really like when you have removed an old terrace. If possible, it is advisable to level the ground before building a substructure for the terrace.

Terrace sub-base on grass/lawn/soil

If you have a softer subsoil of earth, grass, or lawn underneath your terrace, you must first remove the soil by between 40 and 80 cm. Be generous as you will need to do follow-up work at the edges later. Lay a thick weed-control fleece film on the ground. Then you will have less trouble later with weeds growing up.

Into this pit, you pour in crushed stone to a height of 25 to 65 cm and compact it with a 15 cm thick layer of gravel. Vibrate/compact everything firmly into the ground. Now you can set the foundation for the terrace substructure. Washed concrete slabs are usually sufficient here. However, this is more professional with a strip foundation. If you want, you can also use foundation stones. These have about the same function as a point foundation for a terrace.

If you use construction battens, make sure to pay attention to the minimum dimensions. Here, it depends on the length and width. So-called adjustable pedestals are now placed on the foundation. These are usually fitted with a screw thread so that you can adjust the height. Place a rubber pad on each plate as slip protection and damping.

Now you can place construction timber or aluminum profiles on top. Finally, the decking boards are fixed to this terrace substructure with a fastening system, either visibly or invisibly.

Terrace substructure on concrete

Maybe the subsoil is already concreted. In any case, make sure that the concrete slab has a thickness of at least 6 cm. Now you can place the rubber granulate pads directly on the concrete. Of course, these should be placed where you also lay the terrace substructure. Here again, pay attention to the correct spacing.

Finally, the terrace panels are laid again in the desired way. Here, as a rule, you can choose between solid-wood and WPC panels.

Building up a flat-roof terrace correctly

You should be very careful on roofs. The flat roof, and especially the top covering, must not be damaged. First, you should spread out a PE film or a thick weed-fleece layer here as well. This way, a chemical reaction with the rubber pads is avoided later.

Now lay out the rubber granulate pads at the relevant points for the terrace substructure. Note that the roof has a certain size. Ideally, you build yourself a stable wooden frame or one made of aluminum, which serves as the terrace substructure. Directly screwing the substructure onto the roof could possibly lead to leaks.

Finally, you can lay your preferred decking boards here again. In this way, the terrace substructure forms a safe and firm support.

What to do with uneven ground?

The ground beneath the future terrace is not always absolutely level. If possible, you should level the ground here as much as you can. If you want to save yourself the effort, you should excavate the subsoil again and cover it with crushed stone and gravel. This can compensate for differences in height.

If the subsoil has still remained uneven, there are adjustable pedestals for wooden terraces. As mentioned before, these plates can be adjusted in height via a screw thread. This means you can build your terrace even if the ground is uneven.

The rubber pads are placed on the pedestals again as slip protection. On top of that, you can build the terrace substructure out of solid wood or aluminum. Then the terrace panels go on top again.

Calculations & spacing of the battens

With a substructure for the terrace, it always depends on the respective size. If you want to build your terrace yourself, you also have to do some calculations.

For example, pay attention to the correct spacing between the individual construction battens. The distances must not be too large, otherwise the decking boards would later bend over them. This would make the terrace unstable.

The spacing of the individual construction battens for wooden boards should be about 20 times the board thickness. For composite materials, it should be 15 times the board thickness.

The terrace substructure must also not be longer than the length of the decking boards used. Ideally, they can still overhang a bit. In that case, they can later be trimmed at the edges with a circular saw.

Terrace substructure – which material do I use for the sub-base?

Different materials are suitable as a terrace substructure. Below, we present which advantages the different building materials have and which material is best suited for your terrace substructure.

Construction battens made of wood

If you are thinking of a solid-wood terrace, you will find many weather-resistant wood species here. This is then referred to as a durability class. Larch, thermo-ash, bangkirai, or ipé are often used. If you also want to use these woods as the finish for the decking boards, then the terrace substructure should be made of the same material.

It should be noted that, thanks to the support on the pedestals, the construction timber fortunately does not remain standing in moisture permanently. Nevertheless, it is a natural material that can weather over the years.

Construction battens made of aluminum

If the location of your terrace is more often damp and there are also ventilation problems there, then aluminum construction battens are ideally suited for the terrace substructure.

Aluminum is not affected by standing water in particular. The material itself is quite light and yet torsionally rigid. An aluminum terrace substructure is almost insensitive to weather influences. Therefore, it is also significantly more durable than wood.

It may not look quite as nice, but afterward you won’t see anything of this substructure anyway. You will cover it later with your beautiful decking boards. Aluminum construction battens are also often used on roofs for roof terraces.

Construction battens made of WPC

WPC panels are being used more and more often today. You can also use them as a terrace substructure. The hollow beams consist of a mixture of plastic and wood. The material is weather-resistant and dimensionally stable. In addition, it is available in many different colors, which leaves you all options for the terrace substructure.

A WPC substructure can be chosen in the same color as the upper decking boards made of WPC. Note that this type of substructure is only suitable for absolutely level subsoils. Otherwise, the hard material could break under load.

If you are unsure, you should rather rely on wood or aluminum construction battens. The top covering with WPC decking boards is then still possible as well.

Adjustable pedestals for severe unevenness

We have already come across the term adjustable pedestals several times. Admittedly, these small feet with screw threads are a not-so-cheap alternative. In many cases, however, adjustable pedestals make the construction much easier.

As mentioned before, adjustable pedestals primarily serve as a support for the terrace substructure. The upper plates can be screwed in and out individually in terms of height. This allows you to compensate for differences in height.

If you want to compensate for heights over a longer distance, you should first place an adjustable pedestal at the beginning and at the end and lay a construction batten on top. Then you can place the further pedestals in between and bring them to the right height. It is best to put a spirit level on your construction batten. Then you can see whether you are level.

As mentioned before, you can compensate for many unevennesses of the subsoil with adjustable pedestals. Regardless of this, however, we recommend that you level the ground beforehand as far as possible and thus make it flat.

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