Skylights and cupolas

Skylights allow light and ventilation from above.

There are a number of different types of skylight.

Cupolas are skylights which are raised up, often found on flat roofs or in valleys.  Lead flashings protect the joins with the roof. Some were designed to have opening lights to allow ventilation but may have been painted closed or the opening mechanism may be broken. Electric opening systems may be used.

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Cupola skylight in roof valleyJohn GilbertUsually formed in timber with lead dressed over the putty glazing joints. Note the ventilated ridge

 

Skylights can also be found in the roof slope.

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Skylight in roof slopeThe timber framing is covered in lead

Problems:

  • lack of ventilation in the common stair leads to condensation dampness and decay
  • dried and cracked putty allows dampness to seep into timber glazing bars and cause decay
  • large panes of glass can crack, particularly if pinched at a fixing
  • lead cover flashings can be damaged when glass is replaced
  • temporary adhesive flashings rarely last long and can make the problem worse by trapping moisture in the timber glazing bars leading to rot
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A poor replacement solution with fixed lightsJohn GilbertNote the damage from condensation and poor visual appearance

Solutions:

  • cupolas, especially those over the common stair, should have a top vent, usually covered in lead, to ensure through ventilation  
  • lead flashing over joints and glazing bars adds protection but reduces light and may prevent drying of timber
  • prefabricated glazing bars can provide a neat and weatherproof solution
  • do not use standard glass - safety glass or wired glass both hold glass together if it cracks, some prefer the look of safety glass
  • polycarbonate rooflights are rarely of as good quality as having the original glazed skylight formed correctly.

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?

These repairs may be a common or mutual responsibility.

Further information

Society for the Protection of Ancient Buildings Technical Q&A 'Metal Windows'