A poorly maintained roof can be disastrous. Just a couple of damaged or missing tiles or slates will quickly allow water to penetrate a building’s fabric, resulting in damage to the timbers and ceilings below. Where such a problem is left unattended, it will ultimately lead to widespread rot and decay. Then the wind may get under any loose roof covering causing more destruction, eventually needing expensive repairs to put things right.

Identifying roof problems

As with most common property ailments, early detection of roof damage is crucial to prevent more extensive (and expensive) repairs. Learn how to spot these tell-tales signs of further problems.

  • Bits of tile, slate or mortar scattered on the ground or in gutters
  • Slipped or broken tiles on the roof
  • Damaged or missing metal ‘flashings’ and mortar ‘flaunchings’ at roof junctions
  • Chinks of daylight in the loft space or water stains on the floor of the loft
  • Rotten or worm-eaten roof timbers
  • Damp patches showing through on upstairs room ceilings
  • Slates refixed with lead clips or ‘tingles’ as this suggests the roof covering is failing
  • Splits or cracks in flat-roofing materials

For all these reasons roofs need to be regularly inspected with any necessary repairs treated as a priority. While most work should be left to an experienced roofer, checking for problems is relatively easy even from ground level or, if you have them, from dormer windows and roof lights. Problems may also be spotted by inspecting the underside of a roof from loft and attic spaces.

A damaged thatched roof
A prettily thatched roof in Essex is in need of repair to protect the rooms below

Establish a roof checking routine

Bits of slate, tile or mortar found lying in gutters or on the ground around a building are often the first sign of trouble. Always take them as a warning sign that the roof may need fixing.

As part of a twice-yearly maintenance routine, look at the roof, preferably using binoculars, to identify potential problems early on. This may need to be done from a neighbour’s garden. Methodically examine each aspect for slipped, missing or broken tiles. In addition, pay attention to junctions and places where the roof changes direction. Look for damaged or missing ridge and hip tiles as well as missing or cracked mortar flaunchings and fillets together with corroded or split metal flashings; when these fail, they are likely to let in water, especially around chimneys and at parapet walls.

If there is safe access to the loft examine the underside of the roof for damage and the floor for water stains or broken pieces of slate or tile. Look out for wet, rotten or worm-eaten roof timbers and try to trace the source of any water penetration. Other vulnerable areas are junctions between the walls and where chimney stacks penetrate the roof, so note any water staining but do ensure it is current rather than historic — try to do inspections during or after heavy rain.

Victorian slate roofs
A row of Victorian slate roofs in south London

Remember that water tends to travel, so it may not be obvious where the problem is. While in the roof space, turn off any internal lights and look for places where daylight is coming through the roof covering.

If roof timbers appear to be damaged or under strain a structural engineer or surveyor should be consulted, but remember that the undulating quality of a roof does not necessarily indicate a defect but might be the result of gentle distortion and settlement over many years. Also ensure that loft insulation materials are not blocking the eaves or hampering ventilation in the roof space as this will cause moisture to build up.

Flat roofs, which may be covered in a variety of materials, including lead, copper, zinc, asphalt or bitumen, should also be carefully examined for holes, splits and cracks as well as areas where water is pooling. There should be a slight fall so water drains away.

Thatch should be relatively maintenance-free but should still be regularly checked and, where problems are suspected, a thatcher should be called promptly. Due to the danger of fire, monitoring and maintaining the chimney stack is a priority; the flue should be swept twice a year.

Roofers carrying out repairs; A partially-constructed roof
Repairs should be carried out by experienced roofers; Roof tiles are laid on laths or battens. When re-roofing today they are generally fixed over underlay or roofing felt

Dealing with problems

Roof repairs are generally best left to a professional roofer who understands old buildings and has the appropriate access equipment. Replacing a few tiles or slates is a relatively simple job but it is also important to work out why a problem has occurred and whether it is indicative of a larger failure. For example, one common issue is ‘nail sickness’ where the fixings have corroded. Other reasons may be frost or wind damage or the decay of wooden pegs or battens.

Another more worrying reason for a roof to fail is because the structural timbers have rotted through or have proved inadequate to support the weight of the covering.

A roofer should be able to undertake minor repairs but it may be necessary to employ a surveyor or structural engineer and a carpenter, all of whom should be experienced in working on buildings of the age and type involved. Remember, that it is very difficult to carry out structural repairs once the covering is replaced.

A Victorian terraced house with a leaking roof; Moss and vegetation growth on a roof
The leak in this Victorian terraced house in west London has caused major internal damage; Vegetation and moss can cause problems

All roofing repairs are best made using the appropriate traditional methods. Where mortar fillets need to be replaced, lime mortar rather than cement should be used. If there needs to be complete re-roofing work, select the materials with care and endeavour to match the type, size, colour, texture and thickness of existing tiles.

Salvaged tiles are available, as are traditional materials to make new replacements. Handmade clay tiles are still produced and most tile factories are able to make ‘specials’ to match items such as decorative ridge tiles. Avoid quick-fix methods such as spray-on foams and other coatings as they increase the risk of timber decay, prevent proper future inspection of the roof and invariably mean that roof coverings cannot be salvaged for reuse. With flat roofs, emergency mastic or tape repairs can sometimes be made but they should generally only be regarded as short-term measures.

On the question of moss, opinions are divided. But excessive amounts will hold water and may cause damage so gentle brushing down is advisable to control excessive build-up.

A pantile roof with a sagging ridge
The sagging ridge of this Norfolk pantile roof adds character and is not necessarily a cause for concern

Visit Roger Hunt’s website at huntwriter.com.

Marianne Suhr and Roger Hunt's "Old House Handbook"
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