CareHomeDeskCareHomeDeskThe assessment framework for deciding whether a flat roof can be repaired or needs full replacement -- and how to specify either.
The decision between repair and replacement comes down to four factors: the age and remaining service life of the existing membrane, the condition of the insulation (wet insulation must be replaced, not dried and left in situ), the number and pattern of existing defects, and the cost comparison. If repair costs exceed 40-50% of the replacement cost, replacement is usually better value over a 10-year horizon. If the existing roof is over 20 years old and has multiple defects, replacement is almost always the right answer even if it costs more now.
Re-roofing can be carried out as an overlay (new membrane applied on top of the existing) or as a strip and relay (complete removal of the existing system back to the deck). Overlay is faster and cheaper but is only appropriate where the existing substrate is structurally sound, the existing insulation is dry, and the loading analysis shows the structure can carry the additional weight. Strip and relay allows inspection and repair of the structural deck, allows the insulation thickness to be optimised, and produces a roof whose remaining service life can be fully warranted. On care homes, where access to the roof during works is limited and disruption costs are high, overlay is often chosen; ensure you are not simply deferring a more disruptive replacement by doing so.
A flat roof replacement specification should cover: removal and disposal of the existing system (specify which elements are included and which are not), structural deck inspection and repair, vapour control layer specification, insulation type and thickness (U-value calculation should demonstrate compliance with Building Regulations Part L), membrane type and grade, upstand height and waterproofing detail, drainage outlets, edge trim and coping details, and any penetrations. The specification should reference BS 6229:2018 (flat roofs with continuously supported flexible waterproof coverings) or BS 8217:2005 (reinforced bitumen membranes) as appropriate for the system chosen.
For flat roof replacement, use a contractor who is accredited by the relevant system manufacturer and can issue a manufacturer-backed insurance warranty (typically 10, 15 or 20 years). The National Federation of Roofing Contractors (NFRC) maintains a list of approved contractors by system type. Ensure the warranty covers both the membrane and the workmanship -- many warranties cover only the membrane material, not installation defects. Ask for a BBA or KIWA certificate for the membrane system specifying the installation conditions and performance criteria.
CareHomeDesk gives you compliance checklists, maintenance logs, and contractor management tools built around exactly this kind of knowledge.