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Faults and defects in the waterproofing layer of the building envelope

10. November 2020 | Ing. Lukáš Lucký

The waterproofing layer protects the building from the ingress of water and moisture into the structure. It is used wherever the structure is stressed by water, moisture or steam. In older buildings, the areas hit hardest are roofs, balconies, loggias and foundations. Asphalt strips, often commonly referred to as IPA, are the most common. IPA is the popular name for asphalt waterproofing strips used in the 50s and 80s of the 20th century. We recommended to leave the choice of suitable waterproofing to the expert. Waterproofing, like most materials built into a structure that are exposed to external influences, has a limited service life. A minor failure of the waterproofing layer can lead to water penetration and cause significant damage to the structure.

Is flat roof suitable?

A flat roof is most stressed by external weather conditions. During the year it drains out rainwater, in winter it is stressed by frost and in summer it is exposed to strong sunlight. During its service life, the roof ensures the waterproofing and at the same time insulates the roof cladding of the roof structure. According to the Slovak Roofers Guild, roofs in Slovakia are not in good condition and they require major renovations. The roofs built prior 1989 are in the worst condition. A significant percentage of defects was caused by poor quality works and design, use of unsuitable materials, poor implementation, weathering and neglected maintenance. For the proper functioning of the roof, it is very important to keep the slope of the roof so that the rainwater drains smoothly from the roof (prevent water pooling).

Before starting the renovation of the roof, we recommend hiring an expert to inspect the condition of the roof. The expert will subsequently draw up a comprehensive renovation project. With the original roofs, consider replacing the entire structure (disassembly of the roof to the load-bearing structure). After renovation, the roof must meet the minimum building and physical requirements set out in the STN 73 0540-2. On January 1, 2021, new and stricter guidelines concerning the heat transfer coefficient came into force. The target values are divided into required and recommended. The original roofs no longer meet these required minimum values defined by the standard.

Balconies and loggias

The balcony is a horizontal supporting structure bounded by railings. It is a structure suspended in front of the facade and is not protected from the weather. Balconies, as exterior horizontal structures, are particularly stressed by the weather. Water flowing through the broken waterproofing layer into the supporting structure causes gradual corrosion of the balcony slab reinforcement. In winter, the water in the structure freezes and increases its volume. The frozen water disrupts the concrete, which gradually loses its strength. For this reason, it is necessary to take into account the opinion of the structural engineer and design a renovation solution that would take into account his findings.

The loggia is also a horizontal load-bearing structure, bounded on two sides by load-bearing structures, recessed into the facade of the building. In some cases, the floor of the loggia also forms a part of the roof. Due to their design, loggias are more protected from the weather. However, this does not mean that the loggia’s floor is not stressed by water, for example during heavy rain. The water that flows through the damaged parts of the waterproofing will cause wetting of the structure, i.e. the ceiling of the space under the loggia. The structure of the loggia is in some cases similar to the structure of the roof and must meet the minimum thermal insulation requirements. Poor thermal insulation of the loggia’s floor may cool the ceiling of the space under the loggia and sooner or later, mold may appear. When renovating balconies and loggias, we recommend choosing complex waterproofing and construction solutions.

Will the renovation of waterproofing layers help?

The absence of a waterproofing layer or damaged waterproofing under the base plate causes moisture to be released from the subsoil. Water may start to seep into the structure through the damaged part of the waterproofing and negatively affect the floor, including its upper layer (it may slowly deteriorate and deform due to moisture present). Renovation of the floor waterproofing layer is an extensive process and requires the original floor to be removed the ground level or even foundation. Before carrying out any form of restoration works, we recommend contacting an expert who will carry out a detailed analysis of the condition of the structures.

From the implementation and financial point of view, it would be cost-effective to renovate waterproofing layers of roofs, balconies and loggias along with the building envelope. If the client decides to renovate the building step by step, the designer should take into account the renovation stages and help plan individual steps. At the same time, the implementation documentation should include a stage addressing the renewal of the building envelope. Many construction particulars in the renovation of roofs and balconies are directly related to the facade.

Our recommendations

In the pre-design phase of the project, we advise the client to insist that the roof designer checks the project documentation. The project should also contain solutions for roof/ balcony /loggia waterproofing system. Unfortunately, it happens that contractors replace the waterproofing system solution by an alternative method (“this is how I always do it”). Such alternative solutions are risky in the long run. It often happens that as soon as the warranty period for the works done is over, faults and defects may appear and further repairs are required. Be sure to always follow the project documentation and entrust your project only to experts in the field.


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