5 reasons why water remains on the terrace after rain

• traditional terrace

- boards screwed to joists resting directly on the substrate

- ceramic tiles glued to the substrate

• raised deck terrace

- boards mounted on joists resting on pedestals

- terrace pavers laid on support pads or pedestals

Both types require proper design of slopes and layers so that water can be effectively drained.

Layers of a glued terrace:

1. terrace paver
2. adhesive
3. waterproofing layer
4. compression layer
5. insulation layer
6. slope layer with bonding layer
7. structural slab

Layers of a raised deck terrace:

1. concrete paver
2. terrace pedestal
3. waterproofing insulation
4. thermal insulation
5. vapor barrier
6. slope layer with a 1.5-2% slope
7. bonding layer
8. structural slab

We discuss the construction differences and their impact on water in more detail here:

→ See also: Elevated terrace vs traditional glued terrace

1. Uneven substrate or improper slopes

The most common and unfortunately most serious reason for water pooling on the surface is an uneven substrate or improper terrace slopes.

If the substrate

• does not maintain a slope from the building to the terrace edge/drain
• was made unevenly
• contains local depressions,

water will collect in the lowest points - regardless of the type of surface.

If you are wondering whether the slope on your terrace is appropriate: See also: What slope should a terrace have for water to drain off? What percentage of slope is recommended for a terrace?

Care should be taken to ensure that the design is tailored to the specific terrace - proper detailing of the substrate layers along with slopes is necessary. However, another equally important issue is contractors adhering to the drawings - avoiding modifications based on their own experience or the use of substitutes.

In such cases, even perfectly executed slopes do not ensure proper water drainage - water will remain directly on the surface of the material.

If the problem is the material itself from which the surface is made, the only solution is replacement with a material with appropriate technical parameters.

The choice of material is crucial for water drainage:

See also: Types of surfaces used on raised deck terraces

1. Exceeding permissible loads

Each material has a specific load-bearing capacity and strength, exceeding which leads to permanent deformations - ceramic pavers may crack, boards may bend, or local depressions may form where water can accumulate.

It is very important to know the load-bearing capacity of materials when deciding on their selection; such information is usually found on the packaging or on the manufacturer's website.

Without knowing the load-bearing capacity, mistakes can be made such as:

• placing excessively heavy objects in one location (jacuzzis, pools, heavy planters)
• creating point loads on the terrace without securing them with additional supports

This problem also applies to raised deck terraces - therefore the placement of pedestals must be adapted to the planned use of the terrace.

More about load-bearing capacity and permissible loads:

→ See also: Loads and load-bearing capacity of a raised deck terrace - what is worth knowing?

1. Incorrect selection and placement of pedestals

In raised deck terraces, the following are crucial:

• selecting pedestals with appropriate load-bearing capacity (table comparing pedestals)
• proper placement (drawing showing pedestal placement)
• maintaining the order of structural layers.

In areas where greater loads are planned, such as: planters, pergolas, grills, pools, jacuzzis - it is necessary to increase the density of pedestals to avoid deflections and sinking of the surface.

With such heavy loads, it is also very important to protect the waterproofing, e.g., by using rubber shims (SBR).

We describe the selection of appropriate pedestals here:

→ See also: Adjustable terrace pedestals - application, construction and selection rules

An often overlooked but extremely important aspect is auxiliary components, such as:

• rubber pads under pedestals (SBR)
• joist protection tapes
• spacers between pavers (K3, L3, D3)
• mounting adapters (AD, DAD)
• precise leveling of each paver individually (LE100, LE145)

It is often the accessories that determine whether the surface will be even and water can drain freely.

Additionally, in the space under the terrace, drainage layers can be installed, allowing rainwater to be managed and reused, e.g., for lawn irrigation.

You can find the full list of auxiliary components here:

→ See also: Accessories for raised deck terraces – system elements that determine durability

To prevent water from pooling on the terrace:

• always design a slope away from the building,
• choose materials suitable for outdoor conditions,
• follow load-bearing principles and pedestal spacing
• pay attention to substrate hardness
• use complete mounting systems

In raised deck terraces, an additional advantage is the ability to re-adjust the pedestals at any time. If puddles form due to uneven pavers or the natural structure of the material, leveling corrections usually solve the problem.

However, if the cause lies in the substructure or the substrate, the defect must be removed immediately to prevent damage to the entire terrace.