Central valley double roofs

Typically found in Georgian tenements, such as those in Edinburgh, these roofs have central valley flat roofs or gutters, and downpipes may run inside the flats. They are vulnerable to blockages and overflows and need regular maintenance.

Central valley gutter

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Central valley gutter with skylightsJohn GilbertRaised cupolas that span across the central valley require that the valleys may need to have an outlet on each side of the cupola.

The valley gutter and the drain from it, sit in the middle of your property. Leaks and overflows can cause considerable damage, so these gutters need special attention. 

The rain water outlet may drain to an internal downpipe or be channelled through the loft space to a downpipe on the outer walls. A secondary overflow outlet is also advised.

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Wood roll joint

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50mm step with good overlap

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Sump

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Internal drainpipe

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Overflow to external wall

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Problems

These features suffer from the same problems as flashings and flat roofs.

Overflows from blocked downpipes are a common problem, especially with some designs of rainwater sump.

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Blocked central valleyGreyfriars RoofingAnother heavy rainfall could lead to leaks into rooms below. A secondary overflow would be useful here.

Maintenance

There should be an access hatch from the loft to the valley gutter.

  • clean valleys every autumn to remove leaves and debris, and reduce risk of overflow
  • install duck boards to protect leadwork from foot traffic
  • ensure access through the loft is safe - consider a folding ladder, crawlboards inside the loft, and lighting
  • make sure the access hatch is kept locked
  • a leafguard over the drain outlet may be considered but these themselves can block, so will need regular cleaning

Replacing and repairing

Repair and replacement is generally the same as for flashings and flat roofs. If snow is a problem in your area, consider installing heat trace cables to prevent damaging build ups.

Alternative materials

If you live in a listed building or a conservation area, you may be required to replace with lead as it has a much longer lifespan than other materials.

Single membranes or liquid applied membranes may be used as alternatives in other cases.

Professional help recommended?

Although the work may appear straightforward, ensure your builder or tradespeople have the skills for the job. If in any doubt, get professional help to specify and organise the repair.

Who pays?

Roof repairs are normally a common responsibility.

Further information

Lead as a building material

Flat roofs

Lead flat roofs

Andy Davey, Bob Heath, Desmond Hodges, Mandy Ketchin and Roy Milne, 'The Care and Conservation of Georgian Houses' (4th edn, Butterworth Architecture, 1995)

 

See also