RICS publish paper on Japanese knotweed


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The Royal Institute of Chartered Surveyors (RICS) have released a draft information paper on the effects of Japanese knotweed on residential property. The consultation paper involved many experts within the field of Japanese knotweed and their findings have now been collaborated and released by the RICS.

Why publish a paper on Japanese knotweed?

The RICS decided to publish a paper on the issue of Japanese knotweed within residential properties to help property companies and individual owners with some of the major issues surrounding Japanese knotweed. The paper seeks to clarify any legal issues that property owners may face when dealing with Japanese knotweed and how this may affect the value of their property. When discussing the main issues, the RICS paper looks at why Japanese knotweed is a problem, the main damage that the plant can cause to property and the most effective Japanese knotweed treatment methods.

Why is Japanese knotweed a problem?

Japanese knotweed can be a problem because it grows quickly and strongly while out-competing indigenous plants that can kill them off. In 1905, the Royal Horticultural Society declared that Japanese knotweed should not planted in gardens unless it was “kept in check”, this did not however stop the spread of Japanese knotweed as by the 1930’s it was already affecting house prices, with East Cornwall being badly affected and reportedly houses being worth £100 less if Japanese knotweed was present in or around their properties. In 1981, the Government finally took steps to try to solve the problem of Japanese knotweed by making it an offence to “plant or otherwise cause Japanese knotweed to grow in the wild”.

The RICS published the paper due to the increased reports of mortgage lenders who have refused mortgages due to Japanese knotweed near a property. These incidents became prominent news stories and many property companies feared that house sales could fall so the RICS has taken the step to publish a paper on Japanese knotweed and residential property.

CML and BSA seek assurances

The Council of Mortgage Lends (CML) and the Building Society Association (BSA) are the two leading organisations whose members account for the majority of mortgages on residential properties in the UK. Having consulted their members, the CML had indicated that there was a general reluctance amongst their membership to give mortgages on properties that were infected by Japanese knotweed. Of those who would consider giving mortgages on a case-by-case basis, they wished to see a form of Japanese knotweed treatment and a commitment for a future programme of treatment. Japanese knotweed also caused a problem to property owners as many insurance companies would not pay out for damage caused by Japanese knotweed or would pursue neighbours for costs if the Japanese knotweed originated from their land.

How big of a problem is Japanese knotweed?

The RICS believe that Japanese knotweed causes a problem for the residential property market as many companies and individuals suffer overreactions or misunderstandings about the plant. Much of the serious damage that Japanese knotweed causes includes: Drains becoming cracked and/or blocked with clumps of the plant growing in them, patios and paths having to be replaced, poorly constructed outbuildings (garage, shed etc.) being overwhelmed. In conjunction with these problems, only licensed companies may dispose of contaminated soil and this can have serious implications for home-owners who wish to develop their properties further. The process of removing the contaminated soil can also affect the price that Japanese knotweed treatment costs.

Identifying Japanese knotweed

Identifying Japanese knotweed can be a major problem for some home-owners and the RICS paper has published guidelines to follow if you think you have a Japanese knotweed infestation. During the growing season for Japanese knotweed May-October, then the four main signs that the plant is Japanese knotweed are the leafs, the leaf stems in a zigzag pattern, the main stems and the flowers. Some home-owners may choose to try to conceal that their property is suffering from Japanese knotweed by trying to remove it themselves and cover the area that was affected. It is important that a professional carries out a survey to ensure that there is no Japanese knotweed present or likely to be present.

Japanese knotweed treatment

The Royal Horticultural Society state on their website that removing Japanese eradication “requires steely determination”, in the draft paper the RICS looked at the different methods available for treating and eradicating Japanese knotweed. The treatments that the paper discusses include; excavating the plant and its roots, on site burial or encapsulation with membranes, biological control and chemical controls. The RICS reports states that in most residential situations a planned and managed chemical control treatment is the most realistic option.

How much will Japanese knotweed treatment cost?

The RICS paper has shown a breakdown of the costs of Japanese knotweed treatment and on average how much a home-owner should expect to pay, based on the severity of their problem. The paper includes such things as treatment costs, replacement costs and legal fees among many others. The RICS paper does not however state the costs of removing and disposing of any contaminated soil. It should be remembered that costs can vary based on a number different issues including the company used, the location of the home and the severity of the Japanese knotweed intrusion. Home-owners should also be wary that if they wish to sell their property then most mortgage lenders will wish to see a plan for the future treatment of Japanese knotweed. The RICS paper on Japanese knotweed states that property owners should seek assurances from their contractors and have a detailed Japanese knotweed management plan in place.

The full report can be found HERE.

More information on Japanese Knotweed

For more information on Japanese Knotweed, click on the links below