ᐅ Roof Covering for a 8° Mono-Pitch Roof – Bitumen?

Hello house building experts,

I have been silently following for some time and would like to ask my first question.
We are currently planning a two-story house with a shed roof. The roof will cover a base area of 10.75m x 8.40m (35.3 ft x 27.6 ft) plus a 1.0m (3.3 ft) continuous roof overhang, resulting in a total roof area of 130 m² (1,399 sq ft). The roof is oriented approximately 10 degrees to the south, sloping upwards toward the north, and will be constructed as an insulated roof without an additional intermediate ceiling or attic space. Our structural engineer has designed the roof with bitumen roofing membranes covered by slates. His reasons are the low costs and the reduced noise during rain compared to metal roofing. However, we are now questioning whether bitumen membranes make sense in terms of durability.

We are also planning a photovoltaic system, and ideally the roofing should last at least as long as the solar panel system so that replacement can be done simultaneously. Flat roofs are often made with bitumen membranes, so what are the arguments against using it here? Is bitumen an unsuitable substrate for photovoltaic systems? What do the experts recommend?

- Bitumen membrane as currently planned
- Synthetic membrane/EPDM membrane (I was recommended the Alwitra membrane)
- Metal roofing (corrugated or standing seam?)
- Tile roofing (probably not practical given the low roof slope)

Like most homeowners, we are of course very concerned about not having excessively high construction costs due to the current price increases.

Best regards,
Kevin

I can’t speak from personal experience. However, bitumen membranes would not be an option for me. At first glance, the material seems inexpensive. But I just have to look around my neighborhood to see how bitumen roofs age: weathered, patched, blotchy, full of holes, and unattractive. Not to mention the cost of disposing of this material today, which where I live is even higher than asbestos. In my opinion, there are areas of a house where you should NOT cut corners. The roof definitely belongs to that list. It protects the rest of the building structure. If it’s structurally feasible, go with tiles. And that’s that—for several decades. With bitumen, you’ll be frustrated within five years.

HausiKlausi schrieb:

If it is structurally possible – put bricks on it. And that’s it. For several decades. With bitumen, you’ll be annoyed in 5 years.

At an 8° roof pitch? Do you think that would work?

At 8°C (46°F), working with bricks becomes difficult. Everything I have seen requires at least 11°C (52°F).

The appearance is probably not that important, since an 8° (8°) single-pitch roof on the second floor is hardly visible or only very limited. In addition, there will be photovoltaic panels on top. For me, the technical feasibility is much more important than the appearance.

There are tiles that, according to the manufacturer, can be used from 7° (7°) pitch upwards (Bra** 7f+), but the regulations of the German roofing trade specify that tiles should not be installed below 10° (10°). Many believe that tiles at such a low slope do not provide sufficient protection against water penetration.

This leaves mostly bitumen or metal roofing as options...

If the manufacturer specifically approves the product for low roof pitch (whatever they have done differently), I see less of an issue there.