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Metal roofs and flashings

What to look for:

  • Splits
  • Creep
  • Pitting
  • Rucks
  • Wind damage
  • Rippling
  • Pinholes
  • Flattened upstands

Keep roofs free from debris, leaves and build-up of moss. A ‘flat’ roof should have a slight fall so that water can drain away. Mastics and repair tapes are short-lived and may conceal the real sources of leaks without fixing underlying problems. Employ a specialist to carry out proper repairs to lead or zinc roof coverings and valley gutters.

In historic building work a company who are members of the Lead Contractors Association (LCA) should be employed, generally using techniques as specified in the manual of the Lead Sheet Association.

Replacement lead should be the same thickness (code) as that being replaced. Generally flat roofs are laid in code 8 lead or above, with historical flashings rarely being less than code 6.

Splits and pinholes in lead can be patch-repaired by ‘burning in’ a new piece. This sort of ‘hot work’ requires an experienced contractor, who will take all the necessary fire precautions.

You will probably find that your chimney has lead or zinc flashings (metal covers at the junction of the chimney stack and the roof). Underneath these are ‘soakers’, which tuck under the slates or tiles. To keep water out effectively, these must be kept in good repair. Sometimes there is a mortar and tile slip ‘fillet’ installed: this may be appropriate to retain on some buildings but if you have to repair it, you should incorporate soakers underneath (if the type of roof covering allows it).

Historic valley, box and parapet gutters are often constructed with falls, drips (steps) and laps that are unsuitable for the lengths of lead used or the movement it experiences through expansion and contraction. In this instance consideration should be given to reforming the gutter (in practice this often involves adding additional drips which raises the height of the gutter). Professional advice should be taken as careful detailing is required to ensure this is not detrimental to the appearance of the roof. Proprietary lead expansion joints which incorporate a neoprene section are available where reforming gutters is not possible although care should be taken with their use and it should be noted that their lifespan is limited when compared with that of lead.

The use of sacrificial flashings should be considered as this should make future maintenance less onerous. These are sections of lead sheet, held in place over valley flashings using lead, copper or stainless steel clips, which take the immediate run-off from the roof. Sacrificial flashings are generally in a lower code than the flashing they protect and are cheaper and easier to replace once deteriorated.

Many substrates are unsuitable for laying lead due to rough surface textures restricting moment or compatibility issues which can deteriorate the lead. A building paper or specialist geotextile underlay for leadcan be incorporated to overcome this. With some timber substrates (including many plywoods) building paper should be used rather than a geotextile to prevent damage from tannins emitted from the wood.