Advice & Guidance
Structural Issues
It is unlikely that you will discover significant structural problems whilst carrying out routine maintenance tasks. Diagnosing structural defects requires expert analysis and judgment by the inspecting architect or surveyor with help from a consulting structural engineer if necessary.
That said, volunteers do have an enormous
advantage over any visiting professional in that they can monitor changes in
the building informally. They may also
be the first to notice any unusual or progressive cracks, bumps and
bulges.
However, in order to avoid the recurring problem of the ‘discovery' of apparently new structural defects, cracks or distortions, which have in reality existed for years without ill effect, it is very important to make sure that such matters are recorded in your logbook and referred to in the routine professional inspections carried out by your architect or surveyor.
It is also important to remember that some movement is merely seasonal and that cracks that open and close over the course of a year are often harmless.
The most likely source of structural distress is the ingress of water, so maintaining gutters, downpipes, gulleys and drains is fundamental to keeping the structure of your building safe from harm.
Structural problems related to water ingress are common to buildings of all ages - in reinforced concrete buildings continual dampness can lead to the corrosion of the metal reinforcement, whilst in older buildings it may lead to the loss of mortar from the joints as well as timber decay and possibly insect infestation internally. In old buildings with shallow foundations, softening of the soil due to blocked or absent drains can also lead to foundation problems and consequent structural movement.
Most
people are familiar with the idea of underpinning weak or unstable foundations
but remember that historic buildings may have survived for many centuries
without problems so we can reasonably expect them now to be at ease with their
surroundings and well adapted to conditions in the sub-soil.
Where foundation problems do occur they are often indicated by fresh and progressive cracking. The cracks are usually tapering and often, but not always, diagonal.
In most cases, the cause may be related to changes in site conditions such as:
- The unchecked growth of large trees in areas of clay sub-soil.
- Changes in the amount of moisture in the sub-soil due to defective drainage.
- The drying out of the sub-soil due to new land drainage schemes adjacent.
- The washing away of fine grains in sandy or gravely soil allowing the sub-soil to compact.
Retaining walls can occasionally be problematic too. As burials take place over the centuries, the surface ground level rises. Retaining walls therefore end up holding back a greater height (and weight) of soil than they were ever intended to do leading to the risk of collapse.
The
presence of metal in historic buildings (and in particular in modern reinforced
concrete) can cause specific problems related to rusting and expansion of the
metal. Spalling of the edges and corners
of blocks of masonry may indicate corrosion below the surface. This can require serious and expensive
remedial work and is a situation where skilled structural engineering advice
must be sought.
Action point: Note down the position of any existing cracks, bulges or other such defects in your logbook. You might find it helpful to take record photographs to aid identification. Take advice from your architect or surveyor about whether monitoring is required. If there is a concern that there is significant, fresh change in any cracks it may be advisable to discuss your concerns with your architect or surveyor who will be able to advise whether the opinion of a structural engineer is required. This also applies if a crack has been recently repointed and continues to widen.
© SPAB 2010
