Repairs: roofs and rainwater goods

In the context of the projects relevant to this section, you will probably encounter 3 main categories of roof:

• modern pre-trussed rafter frame assemblies (sometimes called TRADA roofs);
• traditional 'cut timber' dual pitched (or single pitched lean-to) styles;
• flat roofs.

The first two types are most commonly covered with slate, clay tiles or, within the comparatively recent past, concrete tiles. There are numerous other coverings, of course, including various forms of coated sheet steel or other sheet metal. Flat roofs are usually covered in some form of bituminised felt or one of the modern plastic polymer equivalents, but may also employ sheet lead, copper, sheet aluminium and a variety of other materials depending on application.

Less common coverings include:

• asbestos cement and fibre cement slate profiled sheet roof coverings;
• profiled/plastic coated metal (PCM) sheet roofs;
• built-up sheet metal roofs (typically on a timber frame), e.g. sheet copper-slate-covered cupolas.

Other categories of construction, such as the 'cruck' framed roofs in old timber frame structures, or domestic properties with steel roof lattices (such as in the Trusteel™ prefabricated wall and roof design), are beyond the scope of the 'traditional building repairs' discussed here.

The main question when approaching a roof repair must always be:

Will the property be mortgageable once the improvements have been carried out; or is a mortgage valuer likely to consider that the works have compromised the property?

Having said that, you probably have to accept that older roofs are unlikely to achieve the standards set by the most recent Building Regulations.

Roof work often involves tackling a wall that is a party structure. If so, you need to serve a Party Wall Act notice if the fabric or loading is being modified in any way (see party walls).

Adding to the weight of the roof is a structural modification, and under the Building Regulations (Approved Document A) this work needs approval (a Building Notice is usually sufficient).

When carrying out any roof repair or reinforcement works:

• check the condition of all the flashings;
• check the condition of any timbers, such as wall plates or trimmers around chimneys, because any minor damp trickling through can cause timbers to badly soften without any tell-tale mushroom growth to highlight the problem;
• check the condition of any fixing nails – if the roof is old, these may have rusted away, and the added weight of roofers and the vibration of repairs could trigger slippage and spreading out of the roof timbers: re-fix by screwing or nailing (a perforated galvanised strap to secure components together, before doing other works is a sensible precaution);
• look for any old repairs that were intended to cure the problem but have in fact only deferred it – for example, purlins or hip boards propped on ceiling joists that will eventually start to bend themselves under the load, which has only been temporarily redistributed but not properly supported);
• check the condition of any adjacent roof;
• check the weight of the new covering, if a replacement is intended (often, replacement concrete tiles are found to have overloaded an old roof, with no reinforcement works to the old timber frame to accommodate them);
• when re-roofing (i.e. a new covering, rather than repairs to the old), check that the valleys are left ‘open’ (rather than closed by overhanging tile edges) to ensure any leaf blockages or mould deposits can be raked out quite easily.

Unless you observe any very significant shortcomings and the roof is currently performing adequately, it is often best to leave well alone, although a cautionary comment to the building owner may be appropriate to advise that eventually an improvement or repair might be required.

If you are appointed by the client in the role of clerk of works, you will also get some idea of the quality of site workmanship and the need for early intervention by observing the following:

• Stacking of slates or tiles on the roof before they are laid – It is particularly important to ensure that the load is distributed evenly over the roof rather than stacked up in one corner, which can completely overload either the battens or possibly even the rafters beneath. Poor stacking will also give you an early warning of worse to come if you are not quick to check the progress!
• The quality of work from felt upwards – For example, the felt needs to be sufficiently loose to allow water to drain beneath the battens; and if it is a traditional roof, any timber battens should be stopped off 200mm (about 8 inches) from flues to reduce fire risk.
• Are properly tanalised/chemically treated timber battens being used to resist timber decay? – Counter-battening may be appropriate in particularly exposed positions.
• Is the gauge suitable? – Less scrupulous roofing contractors and builders may be inclined to ‘pull the gauge’ in order to reduce the number of rows of tiles used and slightly reduce costs. The effect of this, of course, is that there is insufficient lap on the tiles and increased risk of driven water penetration.

The basics should serve as a useful aide memoire when you are out on a site inspection.

Tiles stacked on roofs to spread the load