Roof covering shed roof 8° - bitumen?

Hello dear house building experts,

I have been a silent reader for some time and would like to address you with my first question. We are currently planning a two-story house with a mono-pitched roof. The roof is to cover a base area of 10.75m x 8.40m plus a 1.0m continuous roof overhang (resulting in 130sqm of roof area). The orientation is approximately 10 degrees south with a northern incline, and the roof is to be constructed as an insulated roof without an additional intermediate ceiling or attic. Our structural engineer has planned the execution with slate-covered bitumen sheets. His reasons are the low cost and the low noise development during rain compared to a metal roof. Now we are wondering if bitumen sheets make sense in terms of durability?

Furthermore, we are planning a photovoltaic system, and ideally, the roofing should last at least as long as the photovoltaic system so that a replacement can be carried out simultaneously. Flat roofs are mostly also planned with bitumen sheets, so what speaks against it? Is bitumen an unsuitable base for photovoltaic systems? What do the experts recommend?

- Bitumen sheet as currently planned
- Plastic foil/EPDM sheet (I was recommended the Alwitra foil)
- Metal roofing (trapezoidal or standing seam?)
- Tile roofing (probably not practical with the low roof pitch)

Like most home builders, we are of course also very focused on not too high construction costs due to the current price explosion.

Best regards Kevin

I cannot report to you from first hand. But for me, [Bitumenbahn] is out of the question. That stuff looks cheap at first glance. But I just have to look around the neighborhood to see how the bitumen roofs look. Weathered, patched, blotchy, full of holes, unsightly. Not to mention what it costs to dispose of that crap nowadays. At least here, more than asbestos. From my point of view, there are things on a house where you should NOT save money. The roof definitely belongs to that. It protects the rest of the building structure. If it is structurally possible - put tiles on it. And that's that. For several decades. With bitumen, you’ll be annoyed in 5 years.

If it is statically possible - bricks on top. And that's it. For a few decades. With bitumen, you'll get annoyed in 5 years.

At 8 degrees roof pitch? Do you think that will work?

At 8 degrees, it becomes difficult with bricks. Everything I have seen requires at least 11 degrees.

The appearance is probably not that relevant, since you can hardly or only very limitedly see an 8° shed roof on the 2nd floor anyway. In addition, there will be a photovoltaic system on top. I am much more concerned with the technical feasibility than the appearance.

There are tiles that, according to the manufacturer, can be used from 7° (Bra** 7f+), but the regulations of the German roofing trade state that tiles should not be installed below 10°. Many believe that tiles at this low slope are not sufficiently secure against water ingress.

Almost only bitumen or metal remain...

If the manufacturer approves it specifically for low roof pitch (whatever is different about them), I see less of a problem there.