Underpinning foundations may be necessary after eradicating Japanese Knotweed
You may want to look into underpinning foundations if you have suffered an infestation of Japanese Knotweed close to the structure of your property.
The weed is a significant enough threat that the Royal Institution of Chartered Surveyors has published specific guidance on how to assess the risk it poses to buildings.
The highest threat level – tier four – is reserved for when growth is detected within 7m of conservatories and garages.
In a single season, Japanese Knotweed can spread 7m across the ground, and it can reach a height of 3m in just 10 weeks.
However, its deep roots may present more cause for concern where foundations are involved, as at 3m they can draw water from the ground deeper than many other plants might.
This can leave the underground soil dried out, raising the risk of subsidence – something the new RICS guidance should help surveyors to assess more accurately.
If your surveyor raises concerns during a remortgaging evaluation of your property, you may want to seek advice about underpinning foundations that have been disrupted by Japanese Knotweed, other root systems or simply by soil that has become parched due to excessive drainage and inadequate rainfall.