Roof covering shed roof 8° - bitumen?

- Plastic foil/EPDM membrane (I was recommended the Alwitra foil)

I installed it on a flat garage roof with very little slope, maybe 1°.
I can only recommend it, I haven't heard from anyone having problems with it so far, I mean 50 years warranty?
The membrane is fully bonded over [rauspund].

Roof tiles on such flat surfaces are practically just decoration and roof protection. In any case, a waterproof underroof is required, as I have read several times as a layman.

I really like double standing seam. It is for eternity.

With an 8° roof pitch, I can only recommend a flat roof waterproofing.
With bitumen membranes, as everywhere, there are different quality levels. The lowest level is PYE as the top layer. Here, after about 10 years, cracks often occur or the slate chippings slip off. This has to do with the quality of the bitumen.
With the high-quality membranes from the manufacturers, a service life of several decades is no problem. This is also shown by the product warranty granted by the manufacturers. In a standard setup it is 5 years, in the high-quality setup it is 10 years. Of course, a high-quality top layer costs 5€ more per square meter, but compared to the lifespan this is a small sacrifice.

It is similar with plastic membranes. PVC is the lowest standard. FPO or EVA are significantly higher quality because other plastics are used. However, with plastic membranes there can be problems with plasticizers. Due to UV radiation, these can escape and cracks may occur. This happens especially often with PVC membranes.

What you should also know: PVC membranes are laid in a single layer. Usually in a thickness of 1.5-1.8 mm. About one third of this is filler and the actual waterproofing layer reduces to 1.0 to 1.3 mm.
With bitumen membranes, two layers are applied. The first layer is 3 or 4 mm depending on the build-up and the top layer is 5 mm. So with bitumen you get 8-9 mm of waterproofing in two layers. With two layers, the risk of a leaking seam is also minimized because there is an additional layer.

With the bituminous build-up, two layers must be applied = more labor costs
With the plastic waterproofing, one layer is installed with fewer joints = less labor costs

From an expert’s point of view, in this case I would recommend a two-layer high-quality bituminous waterproofing.

The 7° roof from Braas is a nice idea, but only approved with system components from Braas. And since it is only approved as a system, the costs should not be underestimated.

If you have any questions, feel free to ask.

Greetings from Cologne

Thank you very much for this very detailed answer! This makes the tendency towards bitumen sheets even stronger.
You mention a possible lifespan of a bituminous sealing over several decades and then product guarantees of 5 or 10 years. How does that fit together? Even when I compare this with the product guarantee of 50 years mentioned above for Alwitra, that would rather speak in favor of a membrane waterproofing?