Hello,
We would like to have the flat roof of our older building (built in 1970) completely replaced. We are currently gathering quotes. What approximate price per square meter should we expect for the full removal and reconstruction of an 80m² (860 sq ft) flat roof, including KfW funding?
Best regards,
Basti
We would like to have the flat roof of our older building (built in 1970) completely replaced. We are currently gathering quotes. What approximate price per square meter should we expect for the full removal and reconstruction of an 80m² (860 sq ft) flat roof, including KfW funding?
Best regards,
Basti
basti009 schrieb:
What do you mean by saying that everything my roofer says is correct? He says we don’t need any additional slope. But from what you’re saying, I understand that our approximately 2% slope might not be sufficient, or am I misunderstanding?
The roofer believes that the waterproofing membranes are so watertight that additional slope is not necessary.
PS: I just noticed you wrote 2.9% slope = 1.1 degrees, you probably meant 2.0% instead of 2.9, right? caspar.1 schrieb:
I think you only quoted my text, right? At least, I don’t see any reply.What does the airtightness of the roof surface have to do with the slope? Whether there is a slope or not, a waterproofing layer should always be sealed. The slope is there to prevent water from standing on the roof surface, and this can only be achieved with a minimum slope of 5% (approx. 3°). Water should not be allowed to stand on the roof. This is only an indication that standing water on roof surfaces with less than 5% slope cannot drain properly and may lead to ponding.
When planning an appropriate slope, it must be distinguished whether it is to be designed according to the rules for waterproofing (flat roof guidelines ) of the German roofing trade or according to the waterproofing standard DIN 18531: Waterproofing of roofs as well as balconies, loggias, and walkways. Due to differences in the standards, planners should decide or agree in advance under which guidelines the work will be carried out.
Due to deflection and/or allowable tolerances in the evenness of the substrate, the thickness of materials, overlaps, and reinforcements, ponding can occur even on surfaces with a slope of up to 5% (approx. 3°). If standing water could damage the following layers (e.g., tile coverings in mortar beds), adequate drainage must be ensured (i.e., plan for a slope greater than 5%).
In the waterproofing standard DIN 18531, it states regarding roof pitch / slope:
“The waterproofing should be designed and executed so that rainwater does not stand on the waterproofing layer for an extended period, except in the case of intensive green roofs with water retention. A minimum slope of 2% should be planned.”
“For roof surfaces with a slope up to approximately 5% (3°), ponding is possible due to permissible evenness tolerances, deflection of the supporting structure, existing counter slopes, and irregularities at membrane overlaps and reinforcements. To avoid ponding, a slope of more than 5% should be planned.”
Furthermore, DIN differentiates between two application classes (standard execution [K1] and higher-quality execution [K2]):
Application class K1: The minimum slope is 2%, with the possibility to deviate from this recommendation in justified cases: “Roofs of application class K1 can also be planned without slope if the choice of waterproofing meets the requirements of application class K2.”
Application class K2: The minimum slope is 2%, in valleys at least 1%. For occupied roofs with plastic membranes (minimum thickness 1.5 mm), for example, the type of protective layer must be adapted. Moreover, in intensive green roofs of class K2 with water retention up to 100 mm (approx. 4 inches), a lower planned slope is permissible, provided this is taken into account in the choice of materials and execution method.
When planning an appropriate slope, it must be distinguished whether it is to be designed according to the rules for waterproofing (flat roof guidelines ) of the German roofing trade or according to the waterproofing standard DIN 18531: Waterproofing of roofs as well as balconies, loggias, and walkways. Due to differences in the standards, planners should decide or agree in advance under which guidelines the work will be carried out.
Due to deflection and/or allowable tolerances in the evenness of the substrate, the thickness of materials, overlaps, and reinforcements, ponding can occur even on surfaces with a slope of up to 5% (approx. 3°). If standing water could damage the following layers (e.g., tile coverings in mortar beds), adequate drainage must be ensured (i.e., plan for a slope greater than 5%).
In the waterproofing standard DIN 18531, it states regarding roof pitch / slope:
“The waterproofing should be designed and executed so that rainwater does not stand on the waterproofing layer for an extended period, except in the case of intensive green roofs with water retention. A minimum slope of 2% should be planned.”
“For roof surfaces with a slope up to approximately 5% (3°), ponding is possible due to permissible evenness tolerances, deflection of the supporting structure, existing counter slopes, and irregularities at membrane overlaps and reinforcements. To avoid ponding, a slope of more than 5% should be planned.”
Furthermore, DIN differentiates between two application classes (standard execution [K1] and higher-quality execution [K2]):
Application class K1: The minimum slope is 2%, with the possibility to deviate from this recommendation in justified cases: “Roofs of application class K1 can also be planned without slope if the choice of waterproofing meets the requirements of application class K2.”
Application class K2: The minimum slope is 2%, in valleys at least 1%. For occupied roofs with plastic membranes (minimum thickness 1.5 mm), for example, the type of protective layer must be adapted. Moreover, in intensive green roofs of class K2 with water retention up to 100 mm (approx. 4 inches), a lower planned slope is permissible, provided this is taken into account in the choice of materials and execution method.
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