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
caspar.1 schrieb:
I have been a roofer for 40 years, and we install flat roofs with bitumen torch-on membranes 98% of the time. I have sealed all my roofs using bitumen torch-on membranes. Thank you for your reply! The roofer believes that no slope is necessary. I just imagine that without any slope, water will pool on the roof. He said that is not a problem. What are your thoughts on this?
How long should a new flat roof typically last?
Thank you!
basti009 schrieb:
Thanks for the answer! The roofer thinks no slope is necessary. I just imagine that without a slope, water will pool on the roof. He said that’s not a problem. What do you think?
How long should a new flat roof approximately last?
Thanks! Always with a slope
basti009 schrieb:
Thanks for the answer! The roofer thinks no slope is necessary. I just imagine that without a slope, water will pool on the roof. He said that’s not a problem. What do you think?
How long should a new flat roof approximately last?
Thanks! With a flat roof that has less than 5% slope, standing water is unavoidable. I would always recommend building with a slope. You can use tapered insulation or even rebuild the substrate with a slope, which is more cost-effective if the wood structure needs to be replaced anyway.
basti009 schrieb:
How long should a new flat roof last approximately?
Thanks!
With good materials, around 30 years. There are differences in quality, for example.
Bitumen roofing membranes come in many different types and quality levels. Usually, the most common are polymer-modified bitumen membranes and elastomeric bitumen membranes. It may sound complicated at first, but it really isn’t. Polymer-modified bitumen membranes are bitumen membranes with added plastics to the bitumen material. Elastomeric bitumen membranes contain elastic substances added to make them more flexible.
Besides these two main types, there are countless other blends and special forms of bitumen membranes. These differ not only in their composition but also in the choice of carrier materials, usually fiberglass or polyester fleece. Each special type has its own specific technical properties and therefore different areas of application. This makes bitumen an incredibly versatile building material.
To ensure the result is completely waterproof, bitumen membranes are usually installed overlapping and laid in two layers. Anyone who has looked closely at a flat roof will have noticed that it often has a slight green or gray sheen. This is because the top layer is usually coated with slate granules. Slate protects the bitumen membranes from UV radiation. Since bitumen membranes are temperature-dependent, they are also very sensitive to sunlight. In addition to the slate coating, applying gravel on top helps as well. Gravel blocks sunlight and UV radiation, acting as a natural protective shield for the bitumen membranes.
Because of the many different properties and applications, the prices for bitumen roofing membranes range from inexpensive to quite expensive.
Just search online for “differences in bitumen roofing membranes” to find many reports. 😉 caspar.1 schrieb:
Wow, thanks for the response. A few more questions:
1. I believe the ceiling of the house has a slope of about 2 percent. I roughly measured the room heights on both sides of the house, and it seems about right. 11 meters (36 feet) in length with around 20 cm (8 inches) height difference. Is this sufficient for now, or is a steeper slope absolutely necessary?
2. According to the quote, the bitumen waterproofing will be installed in two layers by the company Bauder. Are these reliable?
3. The insulation material used will be 180 mm (7 inches) thick. Is that appropriate?
Thanks a lot!!!
basti009 schrieb:
Wow, thanks for the response.
Two more questions:
1. I believe the ceiling of the house has a slope of about 2 percent. I roughly measured the ceiling heights on both sides of the house, and that seems about right. Is that sufficient for now, or must a steeper slope be achieved?
2. According to the quote, the bitumen membranes will be installed in two layers by the company Bauder. Are they any good?
Many thanks!!! Regarding 1) slope for the flat roof.
The minimum slope for a flat roof in Germany should be 2.9 percent, or approximately 1.1 degrees. However, since this minimum slope is actually very slight, it is better to plan for about 5 percent, or 2.9 degrees.
In the past, “wet roofs” were specifically constructed: a wet roof is a flat roof without significant slope, where rainwater intentionally remains pooled around raised drains. The water level acts as a climate buffer, similar to an extensive green roof.
So, what your roofer says is correct.
Regarding 2) Bauder is a top brand but quality differs within their range:
Bauder KARAT
Polymer bitumen membrane, 5.2 mm thick, with an extremely high mechanical load-bearing polyester composite carrier fleece of 300 g/m², combined with a premium bitumen formula. Surfaced with colored mineral granules in green-white and graphite black. Price approximately 12.00 Euro per square meter (about $).
BAUDER Elastomer Bitumen Membrane PYE Photovoltaic 200 S 5 EN
Material: elastomer bitumen with polyester fleece carrier 250 g/m².
Price approximately 6.00 Euro per square meter (about $).
caspar.1 schrieb:
Regarding 1) Slope for the flat roof.
The minimum slope for a flat roof in Germany should be 2.9 percent, or approximately 1.1 degrees. However, since this minimum slope is actually very shallow, it is better to plan for around five percent or 2.9 degrees.
At that time, they specifically built so-called “wet roofs”: A wet roof refers to a flat roof with almost no noticeable slope, where rainwater is intentionally retained in a controlled way by raised drains. The water level is meant to provide a climate buffering effect, similar to a green roof.
So, everything your roofer says is correct.
Regarding 2) Bauder is a top brand, but even there, there are quality differences:
Bauder KARAT
Polymer bitumen membrane, 5.2 mm (0.2 inches) thick with a mechanically highly resistant polyester composite carrier fleece of 300 g/m² in combination with a premium bitumen formulation. Mineral surface in green-white and graphite black. Price about 12.00 euros per square meter.
BAUDER Elastomer Bitumen Membrane PYE Photovoltaic 200 S 5 EN
Material: Elastomer bitumen; carrier fleece: polyester fleece 250 g/m².
Price about 6.00 euros per square meter. What do you mean by “everything your roofer says is correct”? He says we don’t need an additional slope. But from your statements, I read that our approximately 2 percent slope might not be sufficient, or am I misunderstanding?
The roofer believes that the bitumen membranes are so watertight that extra slope is not necessary.
PS: I just noticed you wrote 2.9% slope = 1.1 degrees, but did you perhaps mean 2.0% instead of 2.9%?
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