MANUAL
The intense changes in industry that have taken place during last 60 years have brought technological changes, also in building technologies. Polymer industry development which has given new possibilities, created previously unknown products that displaced their classic equivalents and finally brought about new approach to existing problems. Up-to-date materials with their outstanding physiochemical factors have enabled launching the changes in building technologies that have consequently changed not only the standard of living but also its cost. This tendency hasn’t miss the building trade. The increase of real estate prices has caused the need of previously unused areas conversion into dwelling flats. The increase of energy prices has caused activities aimed at reducing its consumption costs and consequently reducing the daily building exploitation costs. In construction it has resulted in the increase of importance of materials used in thermal insulation, hydro-insulations, venting and finishing technologies along with gradual launching of these products into attic and roof structure.
Basic parameters
Basic functions and parameters of roof membrane which decide on the quality of the roof material include:
- water-tightness
- mechanical resistance
- vapour-permeability
- resistance to UV radiation
- temperature resistance
Water-tightness
Effective hydro-insulation of roof and attic is one of the main factors conditioning the roof life-span. When this parameter isn’t ensured, other parameters, even if above average, won’t protect the roof from decay processes. Consequently there will be the necessity of roof major renovation. The cost of durable water-tightness isn’t that big, suffice is to match suitable material and ensure correct assembly.
Roof membrane water-tightness is its resistance to the column of water. This resistance is determined by the use of special protecting coating. Depending on membrane type it is a coating based on functional film. Good quality film is effective, durable but rather costly solution. There are also coatings based on impregnation of vapour-permeable fibres but they are of low effectiveness and durability. In result of ageing tests on roof membranes their resistance parameters diminish. Due to this fact it is so important that initial parameters are adequately high so that to compensate for the ageing processes. Water-tightness of membrane is one of its key factors conditioning its effectiveness and durability. It is important that despite ageing process the membrane ensures high resistance to column of water. This is why the water-tightness exceeding several metres column of water is nothing absurd or unnecessary in natural conditions. High initial water-tightness value even if it sounds absurd (it is difficult to imagine several metres of column of water on our roof), is a protection against progressing ageing of material. Considering long and intensive ageing, the resistance of 2-3 metres of water column will diminish to the level of 1-1,5 metres of water column what still is an inconceivable value ensuring high hydro-insulating efficiency in specific conditions prevailing on roof.
Mechanical resistance
The comfort of membrane assembly depends also on its mechanical resistance. The specificity of roofing works is the reason of a situation when tearing and mechanical damage are nothing uncommon. It is important to properly repair such damage. Unfortunately due to additional costs of repairing products and the work necessary to their assembly, such repairing works are of different quality. In extreme cases such repair may not be realised at all. In this way initial roof covering left damaged does not ensure proper safety of roof and attic what will result in dampness. Moreover, in order to prevent from excess decreasing of resistance values caused by ageing processes, membrane should be characterised by max. high resistance values.
Taking abovementioned into account, membranes susceptible to mechanical damage of low resistance values will not ensure the comfort of roofer work and may the reason of necessary supervision of repairing works. Durable membrane will grant us stability and its lifespan. Even long-term decreasing of its mechanical parameters will not influence significantly its functionality ensuring satisfying resistance values.
Vapour-permeability
Vapour-permeability is one of the main parameters that distinguish membranes among other products used for initial roofing. Their low diffusive resistance combined with their water-tightness give completely new possibilities in roof and attic construction technology. Roof diffusive openness prevents from accumulation of excess moisture in roof barrier what protects the roof against progressive changes reducing its parameters that can even cause its decay. Moreover, the lack of necessity of venting slot application between initial covering and thermal insulation prevents from excessive cooling what positively influences cost reduction of energy used for roof heating.
Vapour-permeability is often characterised by the quantity of vapour grams penetrating the material surface (e.g. m2) in time unit (usually 24h). However, such vapour-permeability characteristic may distort actual parameters of compared materials. This is caused by the fact that vapour-permeable value is relative and it depends on research conditions during test being carried out. Formation of large difference of pressure between sides of material tested will result in large amounts of vapour penetrating the material in time unit. If we increase the amount of vapour in one of chambers, we will also increase the final result. Consequently, membrane of low quality may have twice as good permeability values as membrane of high quality.
In order to make an objective assessment of membranes’ diffusive capabilities one should compare the diffusive resistance factor of membranes (Sd) expressed in metres. It indicates the value that is diffusively equivalent to air stratum, so it is a value that depicts the thickness of air stratum comparable diffusively. The lower the factor, the higher the vapour-permeability is and vice versa. Typical of vapour-permeable membranes values are from 0,015 to 0,03 m. One may also meet with values of Sd factor exceeding 0,5 m. Often it depends on waterproof coating being used. If impregnate is used then the diffusive resistance of such membrane will be relatively low. But one should remember that high vapour-permeability is achieved at the expense of its water-tightness and ageing resistance. On the other hand, application of functional film will slightly influence increase of diffusive resistance. Depending on film type, the Sd values will be of few millimetres but in case of low quality and cheap film the values may be of even few centimetres what may significantly influence roof membrane and its vapour-permeability. Moreover, low quality film has limited durability what largely influences membrane lifespan. It is important that vapour-permeable fibres used in membranes are of very low diffusive resistance, even lower than 0,01 m. It is the reason of their extreme vapour-permeability. Application of waterproof coating, depending on its type and quality increases the diffusive resistance and consequently slightly reduces vapour-permeability values. This little loss is compensated for increase of membrane water-tightness. In case of unusually low diffusive resistance of membrane, it is important to check the type of waterproof coating – is it a functional film or only an impregnate. In few cases it may be found out that this is only the fibre that cannot be applied as roof membrane due to its low or even none resistance to the column of water.
Resistance to UV radiation
Resistance to UV radiation is one of decisive factors for durability of roof membrane. The lack of protection against UV radiation may cause gradual reducing of technical parameters of roof membrane depending on exposure time and the intensity of radiation. For this reason good quality membrane should be stabilised on UV radiation.
Membranes that are marked CE are subjected to ageing research including e.g. long-term influence of UV radiation. Such test is a simulation of long-term ageing process. Membrane technical card contains the information about reducing of resistance values after finished research. On the grounds of these results one can compare the quality and resistance of separate membranes. Due to the negative effect of UV radiation on membrane, it is important to limit the exposure time to daylight by quick assembly of roofing. Moreover, after closing of roofing, the attic should be insulated. In other case, UV radiation getting into the attic through window will have an effect on exposed membrane. Indeed, the intensity of such radiation is rather small but during few years it could cause slight changes in membrane structure. The smaller UV radiation, the longer is the durability of membrane.
Temperature resistance
The resistance to extreme temperatures having impact on membrane in tough conditions prevailing on roof is another factor that may have ageing effect on membrane, especially when the temperature is too high. In practice, the temperature on flat roofs is below 80°C what has been confirmed by the observation of bituminous coatings. In result of these observations, no bituminous cracks have been found which could have been a result of exceeding the temperature limit. Presumably, the temperatures on roofs don’t exceed 80°C level. It should be known that short-term influence of temperature above 100°C (e.g. 120°C) on membrane is possible without causing any physical damage. At the same time it should be stated that the flexibility temperature for polypropylene is around 160°C and its smelting temperature is around 240°C. There is also a case of durability of laminate – it is closely connected with quality of lamination technology.
