Overlaying means applying a new waterproofing membrane over the old roof covering.

If the survey provides a clean bill of health then there is no reason why the existing roofing cannot be retained and overlaid. The imposed loading of a new layer or layers to the roof must be taken into account and depending on the overall requirements of the proposed system, it would be prudent to consider sourcing advice from a structural engineer.

• Has poor detail design contributed to ingress problems?
• If a cold roof design, is it poorly ventilated?
• Are the internal conditions unbalanced?
• Is there entrapped moisture or water in the system?
• Is the roof deck formed with Chipboard or Stramit?
• Any of the above issues will need further investigation and possibly more in depth works such as corrective works and, most likely, to strip and replace the existing roof system.

If the problem has been localised then, when required, repairs to the system and/or structure can be dealt with in isolation before embarking on the main task of overlaying.