Hello "mampf". I am only reading your inquiry from 3.2.2017 today. Regarding your questions: 1. The question now is whether a PE foil must be placed between the waterproofing membrane and insulation? Topic: plasticizers or sliding layer. Answer to 1: Yes, it is recommended. Waterproofing should always be protected as well as possible. Consider what load will later act on the waterproofing surface. Even though it may be unlikely, small "snags" could negatively affect movements in the insulation layer. ----------------------- 2. Can EPS or XPS also be used here without concern? Answer to 2: Yes. XPS is mainly chosen for high loads. These are not to be expected in residential construction. --------------------- 3. Is it possible without foil if using PUR laminated with aluminum? Do I then not need a sliding layer? Is PUR immune to plasticizers? Answer to 3: Certainly, it also works "without". But it is a low-cost protection for the waterproofing. And there are no plasticizers in polyethylene. The molecules are very short and unbranched. When they connect during polymerization into a chain, spaghetti-like threads form, which can easily deform in any direction without snagging or resisting. Therefore, they do not require additives of plasticizers to be elastic and can be well processed into films. ----------------- 4. Must a PE foil be placed between the fastening plate and screed in conventional screed (not flowing screed)? Answer to 4: That also depends on the system plate. In most cases, if the edges connect form-fit with each other (like snap fasteners), no further foil to prevent penetration of mixing water into the underlying construction will be necessary.