Parapet Gutters

Leaks in these "secret" gutters often go unnoticed untilĀ rotĀ is found in timbers.

Parapets will have a gutter behind them. This type of gutter is also found behind a cornice with a single stone course above it.  These gutters are long and will normally have steps formed in the lead to ensure the rain flows down to a sump. The sump feeds rainwater into a downpipe and should have an overflow to prevent leaks into the building and to warn people of blockages.

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Parapet with gutter behindJohn GilbertEasily missed leaks in these gutters can lead to rot

Leaks in these gutters often go unnoticed until rot is found in timbers. These timbers tie in a large weight of stone from the parapet.  If the timbers rot there is danger of the parapet stone peeling away from the building.

Problems

  • outlet from sump to downpipe blocked by debris (or snow)
  • shallow gutters overflow in heavy rainstorms which are becoming more frequent with climate change
  • lack of expansion joints in lead linings cause cracks and leaks
  • failing asphalt linings
  • iron cramps or staples fixing the cornice can rust and crack the stone
  • open joints allow plants to take root and the roots can force the stones apart leading to further water penetration problems
  • if the gutter is not properly tied into the wall, a build up of water or snow in the gutter can cause the parapet to tumble
  • if the lead in the parapet is not laid correctly, it will eventually crack through thermal stress and leak
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Blocked sump in parapet gutterGreyfriars Roofing

Solutions

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  • fit a wire leaf cage to prevent blockages further down the outlet pipe - but keep the cages themselves clean
  • fit a secondary overflow to warn of blockages and reduce risks of overflow into the wallhead
  • replace gutter linings with Code 7 or 8 lead laid to a fall, with stepped joints to allow for expansion
  • stepped joints may not be possible with shallow gutters - a  rubberised expansion joint can be used and will have a 30 year life so is likely to need replaced before the lead has failed
  • stone wallhead gutters can be reformed using hot applied mastic asphalt laid over stainless steel mesh and a membrane to allow thermal movement
  • resins set in a glass fibre mesh may be a medium term solution.
  • when releading the gutter, consider protecting copings and cornices with lead caps
  • raise edges of gutters that are too shallow with lead dressed over a stainless steel angle

Professional help recommended?

This can be a complicated repair which needs good supervision so seek professional advice if your building needs this kind of work.

Who Pays?

Gutters are normally a common repair.

Further information

The Building Conservation Directory 'Lead Gutters: Common Defects'