Loss of value due to structural movement
Over the past 30 years we have measured structural movement in older buildings, the results and how we measure for such movement are detailed below:
The two main types of movement found in external walls are
Lateral movement is often caused by a lack of lateral restraint; such lateral restraint is often formed by the internal partition walls, chamber joists, cavity wall ties etc.
When a wall suffers a lack of lateral restraint, e.g. bulges at its mid section or oversails at the eaves, it suggests that the wall is not tied back effectively by the above means, or has been affected by settlement causing the building to tilt.
Vertical movement is caused by the overloading of the foundations. This can occur through too great a load being placed upon them, the failure of a drain running close by, or by trees growing too close to the property etc.
Lateral movement is checked by plumblining the walls from the roof to the ground (where possible), and vertical movement by measuring the amount out of true at specific points on the structure with an electronic level.
The measurements are taken at points where we consider such movement is likely to take place and/or be at its greatest. The measurements are often averaged to give a more representative picture of the movement in the wall. In respect of unevenness in walls, render, plinth bands and the like, allowances are usually made for these factors.
Over many years we have found that:
In the case of lateral movement; 25mm out of plumb for every 50 years of a property’s life is not unusual.
In the case of vertical movement; up to 0.5° is normal, but over 1.0° suggests a settlement or subsidence issue.
Most likely causes of lateral movement were found to be:
q Corrosion and expansion of the cavity wall ties. Alternatively the numbers of ties in the wall could be relatively small thus causing the movement in the outer leaf of brickwork.
q Thermal expansion and contraction of the wall over many years. Masonry like any other material expands when it gets warm and contracts on cooling. Over many years this will cause the wall to move out.
q Lateral thrust from the roof. Roofs tend to put outward pressure on walls and thus cause them to oversail (lean out) at eaves level.
q In the case of external walls with chimney-breasts running up the inner face, the flue gases usually condense on the coldest side of the flue. This condensate runs down the masonry and can react with the mortar causing it to expand. In turn the expansion of the mortar causes a bulge in the wall.
q Settlement of the property in the past.
Most likely cause of settlement/subsidence movement were found to be:
Ø Filled or weak ground with insufficient foundation depth.
Ø Underground watercourse or leaking water main / drain.
Ø Contraction of the ground caused by dry weather.
As regards discounts, there is no set rule, each issue has to be considered based on the problems it causes, the likelihood of a failure in the future, and the cost of remedy.
However as previously mentioned in the case of lateral movement; 25mm out of plumb for every 50 years of a property’s life is not unusual.
Again the case of vertical movement; up to 0.5° is normal, but over 1.0° suggests a settlement or subsidence issue. Therefore if you obtain measurements over 1.0°, a discount may be appropriate.