Created on: 11 May 2026
At first glance, building a patio seems simple: prepare the ground, erect the substructure and then lay the appropriate paving. In practice, however, the planning phase is just as crucial, as it plays a decisive role in determining how durable and functional a patio will be.
A terrace is constantly exposed to varying weather conditions. For this reason, the correct slope is a key factor. It ensures that rainwater is reliably drained away and that no waterlogging forms on the surface or within the structure. If this important factor is not taken sufficiently into account, long-term damage may result.
Table of Contents: Why is a gradient important? | How steep should the slope be? | Take the gradient of the sub-base into account | Calculations | Gradients with system solutions from Eurotec | Ensuring the correct slope and the impact of the decking | Common mistakes & conclusion
Whether it’s a roof structure, a balcony or a terrace – wherever there is a risk of standing water, a gradient must be taken into account during the planning stage. This is the only way to ensure that water drains away properly and that the structure remains durable. The drainage system does not begin with the substructure, but right from the foundation stage.
A lack of or insufficient slope can cause the following problems:
As a rule, a gradient of approximately 2% is allowed for. This corresponds to a difference in height of around 2 cm per metre.
These standard values provide a good guide, but should always be adapted to the specific construction project and the Material used.
Example: Planned terrace with a length of 4 m a: Difference in height b: Length of the terrace a: Angle 1.15° (corresponds to a 2% gradient)
Calculation
a = tan (a) x b b = 4 m = 400 cm
a = tan (1.15°) x 400 cm
a = 8 cm
To carry out the work, the terrace area must be marked out precisely. This can be done easily using string lines or wooden pegs and a taut string. To ensure the string stays in place, we recommend the weaver’s knot. This knot allows you to secure guide strings securely whilst still being able to adjust their height flexibly. The string can be moved along the marking points without having to re-tie it. This allows the desired height – and thus the planned slope – to be set precisely. The string is tensioned at the height of the future upper edge of the decking.
In modern construction practice, laser levelling devices are also frequently used. With the aid of rotating or Cross-line Lasers, the desired height and the required slope can be determined with particular precision. The taut guide line often continues to serve as a visual check and reference edge. In this way, traditional staking-out methods and modern measurement technology are usefully combined.
Height-adjustable levelling feet offer a particularly precise way of creating a slope in the surface layer, especially when building terraces. The PRO levelling feet are suitable for both wooden and stone terraces and are available in various heights. They allow for precise adjustment of the structure and ensure an even slope as well as visible water drainage.
Adjustable feet can also help with uneven sub-bases. Where there is a steep gradient in the sub-base (e.g. up to 10%), the Nivello 2.0 can also be used. It serves to level the sub-base and position the adjustable feet optimally, thereby relieving the load on them. The combination of a gradient in the substructure and in the decking ensures permanent drainage and thus long-term protection.
In addition, Aluminium system profiles are mounted onto the adjustable feet. The various Aluminium system profiles from our range are compatible with the corresponding adjustable feet and ensure a dimensionally stable, durable substructure with a high load-bearing capacity.
Read our technical article if you’d like to find out more about our adjustable feet.
Find out more
The slope should always run away from the building. This prevents water from flowing towards the façade, patio doors or building junctions. In areas directly adjacent to the building, such as patio doors or façades, it is also advisable to implement specific drainage measures. Here, drainage grates can be incorporated at the edges to collect and channel away any water in a controlled manner. Systems such as our Aluminium drainage grate DrainTec ensure reliable drainage and help to reliably prevent moisture damage. Nevertheless, it is important that the gradient is uniform across the entire length of the terrace or, in the case of larger terraces, that multi-sided drainage is considered where necessary, so that the drainage functions properly.
An insufficient gradient may also occur if the terrace structure or the terrace surfacing has not been properly planned. The decking material also plays an important role in this context: the surface texture can determine how water runs off, depending on whether stone or ceramic slabs are used, or whether WPC or wooden planks are installed. With stone and ceramic slabs, water mainly runs off the surface, whereas with wooden and WPC planks, it is also drained away through the joints.
Even with careful planning, mistakes can still occur in practice that disrupt water drainage. Here are a few tips:
The correct gradient is essential for a long-lasting terrace. It ensures that rainwater is drained away in a controlled manner and protects both the terrace surfacing and the entire substructure from moisture damage. It is crucial to take the gradient into account at an early stage of planning and to implement it consistently in the substructure or load-bearing structure. Precise alignment, a uniform gradient, and consideration of the decking material and building connections are essential.
By using coordinated system solutions, such as height-adjustable levelling feet, stable Aluminium substructures or targeted drainage components at the edges, the gradient can not only be achieved precisely but also secured for the long term.
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