UK homeowners could face unexpected problems with plants and trees that could knock down property prices, cost thousands of pounds to remove, cause issues with selling or buying a property, and even result in a lawsuit.
Japanese knotweed can cost over £10,000 to remove in a process that can take up to three years. A knotweed infestation can devalue a property between 5-15% or in some severe cases properties have been almost completely devalued, according to Knotweed Help.
With average UK property prices standing at £244,513, that could mean a loss of £36,677 for home sellers.
Most mortgage providers are unlikely to lend on a property that contains Japanese knotweed and the invasive weed will often put buyers off, making a property difficult to sell.
Knotweed can grow up to 10cm per day and can force its way through concrete, creating large cracks in brickwork and even causing a property to sink, according to a report by Bankrate UK and surveyor experts at Allcott Associates.
“Japanese knotweed can leave homeowners at risk of devaluation and also puts surveyors at risk of costly claims,” said Kim Allcott, of Allcott Associates. It can “cause structural damage to almost any part of a building it can reach, from tarmac drives to drainage pipes and foundations.”
A treatment certificate must be obtained to prove that Japanese knotweed has been removed completely or a property is at risk of not being mortgageable in the future.
If knotweed causes damage to a neighbouring property homeowners may be liable for a lawsuit if it can be traced back to their garden, according to Bankrate UK.
“Japanese knotweed is a nightmare. Most lenders decline on the spot as the risk is too high. Some mortgage providers will even decline an application if the weed is found on the neighbouring property,” said broker Mojo Mortgages.
Giant hogweed can also affect property prices, with buyers likely to make a lower offer to reflect the cost of removal if found on a property at the time of selling, Bankrate UK said.
The plant “causes concern amongst surveyors because of its toxicity,” according to the experts at Allcott Associates. Skin contact with giant hogweed can cause severe symptoms such as skin blistering, burns, pigmentation and long-lasting scars.
UK government advice states: “You must not import, transport, keep, breed, sell, use or exchange, grow or cultivate, or release into the environment certain invasive alien species.
“If you do so, you can be fined or sent to prison for a maximum of up to two years.”
Oak, willow or poplar trees growing close to a property can destabilise foundations and cause subsidence which can lead to structural damage.
This can devalue a home and it is unlikely mortgage lenders will be happy to lend on a property with this type of problem, according to Bankrate UK.
“If surveyors think there’s a risk that a tree could cause structural movement, we recommend soil and root analysis. These investigations are normally in the region of £1,000 and need to be overseen by a structural engineer,” say the experts at Allcott Associates.
Areas particularly at risk are places with clay soils, such as London, Milton Keynes, Colchester, Cambridge and other regions in the south-east of England, according to Allcott Associates.
English ivy can also damage properties by clinging to masonry and mortar, penetrating cracks or joints and shifting roof tiles and guttering.
“Ivy isn't a big problem unless it has grown the side of a house into the loft space. If this is the case, the lender could potentially decline the mortgage application, or hold a retention until it is sorted,” said Mojo Mortgages.
“Removal is straightforward, but the costs of repairing masonry and re-pointing are often around £500 or more if the damage is extensive,” said Allcott.
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