Created on: 11 May 2026
At first glance, building a patio seems simple: prepare the ground, install the substructure and then lay the selected decking material. In practice, however, the planning phase is equally important, as it plays a key role in determining the durability and functionality of the patio.
A patio is permanently exposed to varying weather conditions. For this reason, the correct slope is a crucial factor. It ensures reliable drainage of rainwater and prevents water accumulation both on the surface and within the construction itself. If this important factor is not sufficiently considered, long-term damage may occur.
Inhaltsverzeichnis: Why is a slope important? | How much slope is required? | Considering slope in the substructure | Calculations | Implementing slope with Eurotec system solutions | Correct slope alignment and the influence of decking materials | Common mistakes & Conclusion
Whether it is a roof structure, balcony or patio – anywhere there is a risk of standing water, slope must be considered during the planning stage. This is the only way to ensure controlled water drainage and maintain the long-term durability of the construction. The drainage concept does not begin with the substructure itself, but already within the base layer.
Insufficient or missing slope can lead to the following problems:
As a general rule, a slope of approx. 2% is recommended. This corresponds to a height difference of around 2 cm per metre. These standard values provide good general guidance, but should always be adapted to the specific construction project and the materials used.
In practice, it becomes clear that slope within the base layer or load-bearing layer is essential. If the slope is only considered when installing the visible decking surface, long-term issues are likely to occur. The slope should therefore always be integrated into the load-bearing structure. This can be achieved through:
Example: Planned terrace with a length of 4 m
a: Height difference b: Terrace length α: Angle of 1.15° (equivalent to a 2% slope)
Calculation:
a = tan (α) x b b = 4 m = 400 cm a = tan (1,15°) x 400 cm a = 8 cm
Precise marking out of the terrace area is essential for proper installation. This can easily be achieved using layout pins or wooden stakes together with a taut guideline string. To keep the string securely in place, the use of a clove hitch is recommended. This knot allows guideline strings to be fastened securely while still remaining height-adjustable.
The string can be repositioned along the marking points without having to re-tie the knot. This makes it possible to precisely set the required height and therefore the planned slope. The guideline string is positioned at the level of the future upper edge of the terrace surface.
In modern construction practice, laser levelling devices are also commonly used. Rotary lasers or cross-line lasers allow the required height and slope to be determined with a particularly high degree of accuracy. The taut guideline string often continues to serve as a visual control and reference edge. In this way, traditional marking-out methods and modern measuring technology are effectively combined.
Especially in patio construction, height-adjustable pedestals provide a particularly precise method for implementing slope within the patio surface. The PRO Pedestals are suitable for both timber and stone patios and are available in various height ranges. They allow for precise adjustment of the construction and ensure a uniform slope as well as visible water drainage.
Adjustable pedestals can also help compensate for uneven substrates. In cases of steep slopes within the sub-base (e.g. up to 10%), the Nivello 2.0 can additionally be used. It is designed to level the sub-base and optimally position the pedestals, thereby reducing stress on the system. The combination of slope in both the substructure and the decking ensures permanent drainage and therefore long-term protection.
In addition, aluminium system profiles are mounted onto the adjustable pedestals. The various aluminium system profiles within our product range are compatible with the corresponding pedestals and provide a dimensionally stable, durable substructure with high load-bearing capacity.
Read our technical article to learn more about our adjustable pedestals.
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As a general rule, the slope should always run away from the building. This prevents water from draining 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 dedicated drainage measures. Drainage grates can be integrated along the edge areas to collect and channel water in a controlled manner.
Systems such as our DrainTec aluminium drainage grate enable reliable drainage and help prevent moisture damage. Nevertheless, it is important that the slope remains consistent across the entire length of the patio. For larger patios, multi-directional drainage may also need to be considered to ensure proper water runoff.
Insufficient slope can also result from poorly planned patio structures or decking layouts. The decking material itself likewise plays an important role in water drainage behaviour. Depending on whether stone or ceramic slabs, WPC decking boards or timber decking boards are used, the surface characteristics can significantly influence water runoff.
With stone and ceramic slabs, water mainly drains across the surface, whereas with timber and WPC decking boards, water is additionally drained through the joints between the boards.
Even with careful planning, mistakes can still occur in practice that negatively affect water drainage. Here are a few important tips:
The correct slope is an essential requirement for a durable patio construction. It ensures controlled drainage of rainwater and protects both the patio surface and the entire substructure against moisture damage.
It is crucial to consider the slope early in the planning phase and consistently integrate it into the substructure or load-bearing structure. Precise alignment, a uniform slope progression and consideration of decking materials and building connections are all essential factors.
By using coordinated system solutions such as height-adjustable pedestals, stable aluminium substructures and targeted drainage components in edge areas, the required slope can not only be implemented precisely, but also secured permanently.
At Eurotec, we are committed to providing you with the best possible service at all times. To this end, we have set up a ticketing system that offers you a quick and straightforward way to submit support requests, technical issues and general enquiries directly to our team.
We are happy to assist you with calculations and planning for terrace construction, timber construction, concrete work and facades.
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