Flat Roofs: Repair or Replace?

by | Jul 17, 2006 | Building Surveys and Defects, Maintenance and PPM

For owners and managing agents, the flat roof is often the part of the building that causes the most trouble for its size. A leak appears in winter, a contractor patches it, and the same ceiling stains again the following year. Summer, when roofs are dry and access is easier, is the time to decide properly whether to repair or replace.

Start with a diagnosis

Water travels a long way under a flat roof covering, so the stain on the ceiling is rarely directly below the defect. A proper inspection looks at:

  • the type and age of the covering, whether built up felt, asphalt or a single ply membrane
  • blistering, splits, crazing and open laps
  • upstands, flashings and junctions with walls, which fail more often than the main field of the roof
  • outlets, gutters and falls, since standing water shortens the life of any covering
  • the condition of the deck and insulation underneath, which may need small inspection openings

When repair makes sense

If the covering is generally sound and the problem is local, such as a failed flashing or a damaged outlet, a targeted repair can give years of further service at modest cost. Repair is also sensible where a wider replacement is already planned in a few years and the aim is simply to keep the building dry until then.

When to replace

  • The covering has reached the end of its life and defects are widespread.
  • The deck or insulation is wet, rotten or crushed.
  • Repeated repairs have not stopped the leaks.
  • The falls are inadequate and water ponds across large areas.

Replacement is also an opportunity. Under the revised Part L of the Building Regulations that came into force in April 2006, renovating a roof can bring a requirement to improve its insulation where that is practical. Planning for it at the outset avoids raising roof levels or altering upstands as an afterthought.

Our advice

  1. Inspect every roof at least once a year and clear outlets in the autumn.
  2. Record the age and type of each covering, so replacements can be planned and budgeted.
  3. Specify the work properly and get comparable prices, rather than accepting a single quotation for “a new roof”.

See our Planned Preventative Maintenance and Building Surveys and Defect Diagnosis services, and how we built a ten year maintenance plan for a managing agent.