Roof claddings get faulty even nowadays even though system solutions of most manufacturers are commonly used. Leaks usually occur in the critical details or when unsuitable procedures are used. Moisture conditions of single deck flat roofs with conventional sequence of layers usually make the designers use a steam tight layer or a protective hydro-insulation layer. This solution protects the inside area of the building but it makes it impossible to find a defect of the roof.
From our practical experience we can state that a cause of leaks in the composition of roof layers is usually ambiguous. Like in other fields, it applies that damage usually occurs due to a combination of several faulty factors as a result of which there the mentioned leak in the composition of the roof layers occurs. It can be caused by a wrong combination of selected materials, the designed roof details which cannot be machined, defective construction material or human factor during implementation and other unpredictable causes. However, in the article we do not want to speculate who neglected what and when but we would like to discuss how to find a problem and rectify it in time.
Nowadays the prevailing composition of roof claddings on flat roofs is a single deck roof with the conventional sequence of layers. Generally, on the supporting structure there is usually a steam tight or protective hydro-insulation layer, then there is a heat insulation layer and then the main hydro-insulation layer. From single deck flat roofs of this composition with the standard sequence of layers, storm-water is drained using a two-stage outlet.
For the needs of this article we would also like to explain two basic terms according to the standard ČSN 73 1901 – Roof design. A steam tight layer (or a moisture stop) is a hydro-insulation layer significantly restricting or preventing penetration of saturated steam into the structural construction or the inside or outside environment. Unlike that, the protective hydro-insulation layer is a layer protecting the structural construction or environment against water in case the main hydro-insulation layer breaks.
Generally, the structural purpose of the protective hydro-insulation layer is fulfilment of a function of a steam tight layer. However, it does not have to be the case the other way round, the requirements for its watertight quality are lower than for the protective hydro-insulation layer. Primarily, the moisture stop is supposed to prevent an increased flow of saturated steam from the interior into the roof layers but it does not have to be water resistant. Therefore if we accept that in case of roof damage water could get through the main hydro-insulation layer, it is necessary to stop using the term of moisture stop but replace it with a protective hydro-insulation layer.
We have to realise that if the above specified principles are observed, the use of a protective hydro-insulation layer and two-stage outlet result in achievement of such a degree of watertight construction that in practice it is not possible to find a roof defect unless the actual protective hydro-insulation layer is defective as well. If a defect of the main hydro-insulation layer occurs, the biggest problem is water which gets into the heat insulation layer – not only does it damage the heat insulation material but it also burdens the roof construction excessively. Roof overloading can be decreased at least partially when the protective hydro-insulation layer is drained, ideally directly to the storm-water pipe, the standard ČSN 73 1901 – Roof design in its annex C.1.3 recommends that in cases when you want to drain the protective hydro-insulation into the same sewerage pipe as the main hydro-insulation, it must be connected to the sewerage using a separate inlet and it is necessary to fit a backflow valve onto the interconnecting pipe due to a possible backwater surge during torrential rain.
The above specified procedures thus only solve the protection of the interior premises but they do not say how to find a damage of the roof cladding. Topwet s.r.o. company focused on the issue of detection of a roof cladding defect during development of new detection devices or devices for water drainage from the protective hydro-insulation layer.
TW SIGN KL signalling of a defect of the main hydro-insulation layer with drainage of the protective hydro-insulation layer
TW SIGN signalling of a defect of the layer of the main hydro-insulation
TWO SIGN roof layer defect signalisation duct for the main hydro-insulation
|TW SIGN KL||TW SIGN||TWO SIGN|
If water is found in any of the transparent inspection flasks or reservoirs, it always means the roof is damaged and the situation has to be solved immediately.
Ing. Martin Pánek – technician of Topwet s.r.o. company