Prerequisites for refurbishing a flat roof

Suitability of sublayer for direct installation
Is the sublayer suitable for direct installation of a bitumen or synthetic waterproofing membrane, or is a separating layer needed (e.g. when refurbishing a high-polymer waterproofing membrane)?

A separating layer must be used if there are stresses in the existing waterproofing (brittleness or cracks in the existing membrane). The separating layer will prevent these stresses from being transferred to the new waterproofing package. A separating layer must also be installed if bitumen waterproofing membranes are used on an existing membrane that is not bitumen-compatible. The same also applies in reverse: if synthetic membranes - bonded over their surface with PU adhesive and hot-air welded along the seams - are installed on existing bitumen waterproofing.

Is a dedicated roof drainage system needed?
Ponding, especially on roofs with no gravel covering, always has unwelcome consequences:

• heavier deposits of dirt in these areas.
• mechanical stresses due to the freezing of puddles in winter, and large contrasts in temperature, especially around the edge of areas of water or ice.
  
  

In our experience the most cost-effective solution is to install a sloping layer of Bauder-PIR T tapered insulation panels. The standard panels have a gradient of around 2%.

Is extra thermal insulation desired or even required by the regulations?
In the refurbishment of existing roof structures, the U-value specified in the applicable energy saving regulations is key. If the existing roof structure fails to achieve this heat transfer coefficient, then the thermal insulation will need to be supplemented.

Is the existing roof structure still functional?
In accordance with the guidelines on design and construction of flat roofs with waterproofing, a functional roof can be overlaid with a layer of polymer bitumen membrane - subject to certain conditions.