FORGET flood, fire and earthquake, one of the biggest threats to our homes these days apparently comes in plant form...
So formidable is its reputation that some mortgage companies have imposed a blanket ban on lending where Japanese knotweed is present.
But different lenders have different approaches – and the resulting confusion can reduce a valuation by up to 20% and make the property uninsurable.
Now one Sheffield man is taking steps to tackle the problem.
Chartered building surveyor Phil Parnham, a specialist in residential property, has been commissioned by the Royal Institution of Chartered Surveyors to draw up national guidelines.
His report, due to be published later in the year, should help to decide national opinion on the issue.
Japanese knotweed is a terror whose invasive root system and strong growth can undermine walls and foundations, breach flood defences and damage drainage pipes. So resilient is the weed that its rhizomes can extend 7m in any direction and survive temperatures as low as -35°C.
But the scaremongering has got out of hand, says Phil, of BlueBox partners.
“Because it’s begun to be picked up by lenders as something of concern, it’s having a disproportionate effect on the property market.
“At one time it was asbestos, then it was radon. As the market goes through these panic attacks, lenders get worried and bring in quite draconian conditions.”
In fact, on a domestic scale, knotweed is not terribly damaging, claims Phil.
The root system will seek out weak points if allowed to grow unchecked but specialist firms can eradicate the weed in a matter of months. A systemic herbicide, available from local DIY shops, should deal with the problem effectively within three or four seasons.
And he will be advising the RICS that, even in more serious cases, treatment and making good any damage would cost no more than £14,000 – a fraction of the £50,000 needed to tackle subsidence caused by a large tree.
Japanese knotweed is recognisable by its flat-based, heart-shaped leaves; its hollow, bamboo-like purple-speckled stems and its spiky white flowers.
It is spread by roots rather than seeds, so any waste must be burned or disposed of at designated landfill sites.
Sheffield is no more badly affected than other parts of the country but Phil is aware of more than 20 ‘stands’ of knotweed in the Abbeydale area alone.
He says anyone finding the weed on their property should call in a specialist contractor or treat it persistently with a glyphosate-based systemic herbicide such as Roundup.
And prospective vendors should resist the temptation to simply cover it up. If knotweed appears on a property and it is clear that a previous owner has deliberately concealed it, they could be liable for damages, says Phil.