Solutions to subsidence

Mike Cosy
Mike Cosy
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By Mike Cosy of Coseyhomes, trading as Cosey Rentals 
Chartered Surveyor, Civil 
Engineer and Building consultant.

A FEW weeks ago we looked at subsidence and discussed the causes of structural movement and appearance of crack on the walls of a building. Here we will consider a limited number of solutions.

The severity of the damage can vary considerably from case to case. Once the cause has been established and any additional necessary action deemed necessary is undertaken then a remedial scheme will be proposed by a structural engineer or a chartered building surveyor.

A full underpinning scheme on an average house could be very costly. There are so many factors that will have a direct bearing on cost. In some cases you may have to underpin the adjoining property to avoid what is known as differential settlement.

In a nut shell it means strengthening one side may encourage the side not underpinned to suffer further subsidence.

If a suitably strong layer of ground known as “strata” is at a considerable depth below the foundation then the piles has to be driven deeper adding to the cost.

Vibration from any driven pilling system itself could be causing damage to the subject property as well as to the adjoining houses.

Within the last ten years many other forms of reinforcing the ground or dealing with the results of subsidence has become popular reducing the cost and disturbance considerably. One effective way of dealing with cracks to elevation of walls in less severe cases is known as “crack stitching”

The method consists of cutting slots into the mortar beds between brick courses and placing a 6 mm specially manufactured bars normally one meter in length using grout or resin and mortar pointing.

The number of bars and spacing will be dictated by the engineer/surveyor in charge taking into account the manufacturers of crack stitching materials into account.

If necessary foundation of a property can be strengthened by injection of grout beneath the building. The idea would be to fill all sinkholes. The compound pushes into the soil particles strengthening the loose weak soil and filling the voids.

Pipes are drilled into the ground and grout is injected under high pressure. If your building is suffering from any structural defects it would be much better to engage a structural engineer or a charted building surveyor in order to find an appropriate and most cost effective solution.

Cosey Rentals is regulated by the RICS