Sealing a flat roof under a terrace – without removing the existing waterproofing
This terrace, which is used, also serves as a roof area above living spaces.
After a leak occurred, the damage was specifically located and repaired without removing the existing bitumen seal – using a liquid sealant, reinforced with SA Baustoffe polyester geotextile 110 g/m².
Initial situation
This object is a used terrace above the 1st floor, which simultaneously serve as Roof area for the living spaces below serves.
The roof structure was designed as Inversion roof Executed: A layer of gravel was placed on top of the existing bitumen waterproofing, and concrete slabs were laid on top of that as a terrace surface.
In the area of a room on the 1st floor, Spotty dampness on ceiling and wall The use of the terrace on the 2nd floor remained unchanged – rainwater could still drain away through the joints of the slabs, the gravel layer and via the waterproofing to the roof drainage system.
After opening up a limited area – by removing the slabs and gravel – the cause of the leak became apparent:
damaged connection areas at the parapet as well as several fine cracks in the existing bitumen waterproofing.
Since the building had recently changed ownership and It was not known how many layers of the existing waterproofing were present., A complete dismantling should be avoided if possible. The goal was a targeted, safe repair, without removing the entire roof structure.
Damage analysis and decision-making
After exposing the affected area, the leak could be clearly located.
The damage was limited to the Connection area of the seal to the parapet as well as on several fine cracks within the existing bitumen waterproofing system.
Basically, there were two renovation options to choose from:
Option 1:
Dismantling of the existing waterproofing in the affected area and reconstruction with bitumen sheets.
Since it was not known how many layers of waterproofing were already present, this solution would have meant a high workload, additional risks and unnecessary interventions in the existing roof structure.
Option 2 (selected):
Targeted repair of damaged areas using liquid waterproofing.
Through the combination of liquid sealing and a Reinforced with polyester geotextile 110 g/m² The damaged area could be reliably repaired without removing the entire roof structure.
This approach enabled a technically safe and economical solution, which preserves the existing structure and limits the intervention to the necessary extent.
Why 110 g/m² polyester geotextile was used as reinforcement
Due to the existing cracks, transitions and connections, a liquid sealant alone was not sufficient.
The roof surface required additional reinforcement to permanently absorb movements of the substrate and prevent new stress cracks.
Since this object is a roof area not permanently used Since the material in question had increased mechanical load values, the use of a geotextile with elevated mechanical load values was not technically necessary.
Instead, a specific approach was taken. Polyester geotextile (reinforcement fleece) with 110 g/m² used, which fully meets the necessary requirements for reinforcement within the liquid waterproofing for this application.
By choosing this material, it was possible to forgo a larger, more expensive reinforcement.
This enabled a noticeable cost saving for the client without compromising the quality, function or lifespan of the seal.
The fleece serves as a reinforcing layer within the waterproofing and ensures an even distribution of force over the entire surface.
The material used meets the relevant requirements. DIN requirements for sealing systems and is designed for roof and terrace areas where the existing structure is to be preserved.
Note regarding roll width:
The appropriate roll width depends on the area of application and the details on site – e.g. surfaces, connections or penetrations.
Step-by-step implementation
Step 1: Exposing and preparing the damaged area
To locate the leak, the affected area of the terrace was specifically opened.
For this purpose, the concrete slabs were removed and the underlying layer of gravel was taken out to gain access to the existing bitumen waterproofing.
After the damage was exposed, it became apparent that it was located adjacent to the parapet.
Before the sealing work began, the surface was cleaned and prepared for the subsequent repair to ensure secure adhesion of the sealant.
Step 2: First layer of liquid waterproofing for preparation
After thorough cleaning of the exposed sealing surface, the first layer of liquid sealant was applied.
This serves as an adhesive and leveling layer and optimally prepares the substrate for subsequent reinforcement.
Step 3: Reinforcement with 110 g/m² polyester geotextile
A polyester geotextile weighing 110 g/m² was embedded in the fresh first layer of waterproofing.
The geotextile takes over the reinforcement function, reliably bridges cracks and absorbs movements of the substrate – especially in the sensitive connection area at the parapet.
Step 4: Second layer of liquid waterproofing – complete integration of the reinforcement
A second layer of liquid sealant was then applied, completely enclosing the geotextile.
This creates a homogeneous, seamless seal with permanently reinforced detail areas.
Step 5: Restoring the roof structure
Once the sealant had fully cured, the roof structure was restored.
To protect the waterproofing from mechanical stress caused by gravel and slabs, a geotextile was laid as a protective layer, then gravel was added and the concrete slabs were relaid.
The terrace is now fully usable again – while the roof waterproofing underneath is permanently protected.
Conclusion from the project
Through targeted repair using liquid waterproofing and SA Building Materials Polyester Geotextile 110 g/m² Could the leak permanent and without interfering with the entire roof structure to be fixed.
This solution is ideally suited for Targeted renovations of flat roofs, where an economical and technically safe repair is required.