A leaky flat roof

The flat roof is generally said to quickly leak. Although improved building materials have been available for more efficient sealing, leaks can be a problem even with modern flat roofs. Below you will find detailed information about the flat roof and what causes are often responsible for a leaky roof.

Since the people build houses, there is the flat roof

flat roofs have been around since antiquity - at least. Mainly, they have always been found in regions that are naturally low in precipitation. However, a flat roof has numerous advantages

  • a flat roof is cost-effective
  • low material requirements
  • a flat roof can be quickly and easily increased
  • spaces below the flat roof are not characterized by sloping walls
  • flat roofs can be landscaped or walkable

centuries of attempts to establish the flat roof with us

That and other points are all reasons why flat roofs are always attractive in this country. Already at the end of the late Middle Ages and into the modern age (Renaissance, Baroque) it was fashionable to green flat castle or manor roofs. But always accompanied by the result that the roofs were soon leaking.

New building materials for sealing, new hope

In the second half of the 20th century, progress in the building materials industry took big steps forward. Plastics were increasingly introduced and with that the hope of better sealing flat roofs. So it came in the 60s and 70s of the 20th century to a massive flat roof boom. Moderne Soon, even modern flat roofs were leaking

But the disillusionment should follow soon. Many of the now-built flat roofs were also leaking quickly. So flat roofs over the following decades were once reserved for industrial and commercial buildings. Nevertheless, the technical possibilities developed significantly further.

A new start, a new trend towards a flat roof

Thanks to the new sealing options, flat roofs are once again experiencing a new heyday. Extravagant villas are just as often built with a flat roof as conventional passive energy houses. But by no means should you now assume that the new flat roofs would now be automatically sealed in the medium and long term.

A leaky flat roof is not only due to the materials

Rather, the flat roof construction and the subsequent service life of the 60s and 70s must also be more precisely illuminated. Then you realize that it was not just the materials used that are leading to a leaky flat roof. Rather, it is a combination of several factors.

Planning error

  • Design error
  • Lack of maintenance
  • Incorrect repair
  • Faulty refurbishment
  • Faulty re-sealing
  • The flat roof in planning

Numerous errors can already be made during planning. In Germany, roofs with a slope angle of 2 to 20 degrees are considered flat roofs. The typical flat roof has a roof pitch angle of two to ten degrees. But there are also roofs that have a lower or even no angle of inclination.

The risk of leaking such a roof is enormous. In addition, such roofs necessarily require a gravel pile. The has to fulfill several tasks.

UV protection of the underlying waterproofing

  • Thermal protection of the waterproofing (not so much thermal expansion)
  • Roof weighting against wind suction on a sealing foil
  • Roof weighting to keep the roof tight where it rests Besch The steeper the flat roof, the better safer against leaks
  • It should be noted that the roof pitch should always be as high as possible even with a walk-in roof. The larger this angle, the better and faster water can drain.
The flat roof in the construction

Regardless of the type of roof (thermal, cold or inverted roof), different materials collide in a flat roof.

Bitumen on sheet metal

Concrete on stone and plaster (for example, in attic construction, steps)

  • Plastic on concrete
  • Plastic on sheet
  • Sound knowledge of building materials is essential
  • All these materials react differently under thermal stress. One material expands more than the other. Therefore, it often comes to such transitions to tensions in the material. Explicitly here you must ensure that sealing methods are used, which provide a flexible bridge between the two materials. At roof openings (drain, stand for antennas, fireplace, attic) you will find exactly these places.
Flat Roof Maintenance

If you ask an executing company if their flat roofs are leaking, which answer will you receive? Regardless of whether only meant seriously or actually true, builders are now often of the opinion, they would have, just like a steep house roof, take care of the flat roof only every decades. This is a momentous mistake.

Regular flat roof maintenance is mandatory

You must maintain a flat roof regularly. At least once a year, the roof should be inspected by a specialist to see if it leaked somewhere. At the same time, you can additionally subject the roof to a visual inspection every six months. Preferably you conclude a maintenance contract with a specialist company.

The damage to the building fabric must be avoided

The problem with a leaky flat roof is less that it may get wet inside the room. The sealing in its entirety also protects the building fabric from penetrating moisture. If it rains through your roof, the fabric is already badly damaged in most cases.

This is particularly annoying, because the original cause was usually very harmless.

a small leak on a bituminous sheet

lichen or moss

  • a spot with stagnant water
  • future damage to a flexible sealing bridge between two different materials
  • Therefore, you should look for these possible causes in your visual inspection. The expert then takes the entire construction once a year for handicraft aspects under the microscope.
  • Incorrect repair, refurbishment and new sealing

All causes (incorrect planning, design and execution) can be responsible for the fact that the roof is quickly leaking even during renovation and repair work. It is also possible that the entire substance is already affected by moisture damage, but only a superficial seal is made. Especially fatal: then the water is literally trapped.


A flat roof is complex. It is complex in the planning, as well as in the chosen building materials and construction. But even the regular maintenance is often neglected, repair measures too late and met too little.

Even if the costs for a full refurbishment only become "real" for you when the time comes: the permanent maintenance and care of the flat roof also costs money. But it is many times cheaper than a full refurbishment.

Tips & TricksA full refurbishment becomes even more expensive with the changes to the Energy Saving Ordinance (EnEV), even if you receive funding. According to the changes, you generally do not have to make any corresponding thermal insulation through a thermal insulation composite system (ETICS), if there is still no insulation. However, this looks different for a full renovation. In this case, the insulation according to the EnEV becomes mandatory.

In the case of a flat roof, you basically do not speak of new roofing. Newly covered is only a conventional pitched roof. A flat roof is always sealed.

Of course we keep in the house journal more articles around the flat roof for you. So for building or [sealing a flat roof].

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