Roof Repair or Roof Replacement – Which is Best?

Causes of damage

The main cause of harm to roof structures is decay or beetle infestation, resulting from persistently wet timbers. This might be the result of leaks caused by a defective covering or condensation from inadequate ventilation.

Once the underlying cause is resolved, the timbers will dry and the deterioration will stop. If they’ve been significantly weakened, some physical repair or provision of additional support will be necessary.

Overloading may well cause damage, too. This is usually the result of a poorly-specified change of covering. For example, concrete tiles are much heavier than slates.

Any fires that have occurred in the past can also weaken the structure. In this case, rafters have often been repaired inadequately (or even not fixed at all). Saying that, do be careful not to assume that charred timbers are necessarily faulty; check for actual failure.

Very old roofs will have soot deposits and smoke blackening from the time before there was a chimney. This could be important historical evidence and should not be mistaken for deterioration.

Physical damage is rare in the roof space. It’s mostly the result of poorly executed alterations or previous repairs.

Materials selection for heritage roofs

Unlike the structure, the covering has a limited lifespan. Exposed to the elements with no protection, it’s continually under attack from factors including rain, sun, wind, frost, biological agents and pollutants. These affect different materials in different ways and to varying extents.

Both the covering itself and the fixings are subject to deterioration and must be assessed. Maintenance is essential, because even small leaks can cause very serious damage to the underlying structure over time. The extent to which each type of covering can be repaired varies, but all will ultimately need replacement at some time.

Stone tiles

This is the most long-lived traditional option. Many stone tiles can last indefinitely; it’s the fixings and battens that are likely to eventually degrade to the point where repair is necessary.

Total replacement is unlikely to be required, but it might be necessary to strip and recover. In this instance, most tiles can be saved for reuse, but some will inevitably need replacement. This can be difficult in certain areas as many quarries have now closed.

Slate tiles

Slate also has a long lifespan but, because the units are generally much thinner than stone tiles, they are more subject to physical damage and failure, caused by natural flaws. Patch repairing of damaged slate roofs is often a viable option for extending their life because it’s a fairly homogeneous material and easily sourced.

As with stone, deterioration of the fixings and battens will eventually lead to recovering. Slates in good condition can be reused, but a reasonable proportion will have to be replaced.

Clay tiles

Clay tiles have a limited lifespan. The main culprit is frost, which can cause them to blow apart. Failure rate varies according to quality, design and roof orientation, degree of exposure and changing weather conditions. Recent winters, with frequent cycling between wet and freezing weather, have been particularly hard on these materials.

Over the lifetime of a clay tiled roof, regular patch replacement with well-matched units will be necessary. Eventually the whole covering will need to be removed and new units laid. Previously used tiles can only occasionally be saved for reuse; even if they appear to be in good condition, much of their viable lifespan has already expired.

Thatch

Despite its reputation as a short-lived option, a properly thatched roof can in fact last for in excess of 60 years.

This is very variable, however, depending on location and degree of exposure. This material is subject to decay caused by insects and mould, so the wetter it gets and the more restricted its ability to dry out, the shorter its lifespan. Periodic repair is necessary to maximise its durability.

In particular, the ridge requires regular replacement; limited areas of deterioration can be patched by a skilled tradesperson to delay the need for a full re-thatching.

When the point has been reached where re-thatching has become necessary, usually only the topmost layer needs to be stripped and replaced. In very old roofs, the base coat might still survive from its original construction. This is a precious resource incorporating a wealth of important archaeological information, so if it remains, then you should always look to preserve it.