Many flat roofs look like little lake landscapes from above. The puddles queue to finally be let through. The roof coating, whether made of bitumen or other material does not endure this load in the long term.
Moisture protection for the buildings - the slope in the flat roof
Hardly anything is more effective with a flat roof against penetrating moisture from above, than a sufficiently steep slope and good roof drainage.
Although there are no regulations in Germany in the building regulations for the slope in a flat roof, but even out of pure selfishness, it should be sized large enough. This will eventually save many repairs in the long run and possibly moisture damage to the ceiling.
You always have to remember that the insurance company would not bear this damage. It usually pays only for damages caused by tap water, but not for rainwater.
minimum gradient usually too low
The lower limit in terms of gradient is about two percent in Germany. That's just 1.1 degrees of incline. This slope would not be seen and perceived on most flat roofs.
Only when the puddles are on the roof after a few years or just months, you will notice that this gap is too small.
Recommended slope for flat roofs
Roofers and DIN 18531 for flat roofs recommend at least a gradient of five percent. Again, that's only 2.9 degrees, so still very little.
Material is crucial for tightness on low slopes
EPDM sealing membranes are made of an ethylene-propylene-diene monomer, but the big advantage of this material is its production breadth. EPDM sealing membranes are available up to a width of 15.25 meters and a length of 61 meters.
Therefore, this material is best left with no seam on the roof at all. After all, it is the seams that are the quickest to leak in conventional bitumen welding tracks.
In addition, the seams on bitumen often suffer from frost damage. Also in this area, the EPDM sealing membrane is much more resistant.Tips & TricksIf you want to be on the safe side, you should firstly select at least a gradient of about 7 percent and, secondly, use the still relatively new construction material EPDM as a geomembrane.