Background
A prospective purchaser contacted us following their pre-purchase RICS surveyor’s report identifying significant movement to the rear of a large house.
The surveyor was slightly concerned that the movement might be progressive and could be expensive to repair, and therefore recommended a structural engineer’s report for a specialist second opinion.
Pole service offer
We offered our Structural Engineers General Movement Report, but with particular reference to looking at the cracking at the rear of the property before providing a more general MOT/health check of the remaining walls to the property.
Technical
The narrower two-storey rear projection exhibited textbook subsidence cracking to both the very rear wall and the flank wall. The cracking was between 2‑4 mm wide, which we would put in the medium/moderate category: that is to say by no means trivial but not too serious either.
Our inspection both inside and out indicated that the cracking was broadly historic, due to the extreme discolouration to the cracking, and the lack of any corresponding cracking internally.
We know that the geology in Putney is extremely mixed with granular soils close to the river and clay head deposits slightly further to the South. So because there were no trees nearby, we concluded that the drains were the likely cause of the problem. If the drains are found to leak or are fractured this can cause softening of the soil and/or erosion, leading to a reduced strength of the granular soil as a consequence of the particles being washed away and the soil becoming loose.
Conclusions
We concluded that the drains should be tested and repaired if found to leak. We estimated that drain repairs of the order of £5,000 should be allowed, in terms of contingency planning. It is never realistic to undertake intrusive investigation and testing pre-purchase, and therefore a conservative budget for this work was allowed.
The purchaser was going to completely refurbish the property and would, therefore be remodelling the rear of the property.
