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Japanese Knotweed – a Building Surveyor’s perspective

Japanese Knotweed - a Building Surveyors perspective Img01

Japanese knotweed (Reynoutria japonica syn. Fallopia japonica) is an invasive plant that spreads rapidly. In the Winter the plant dies back to ground level but by early summer bamboo-like stems emerge from rhizomes deep underground. These stems can rapidly grow to a height over 2.1m (7ft), suppressing all other plant growth around it. The leaves are shield or heart shaped, usually with a pale stripe down the middle. Flowers are creamy and arise from the tips of stems. Stems have a red mottled appearance. Eradication requires determination as it is very hard to remove by hand or eradicate with chemicals. This plant has the potential to cause structural damage to properties by exploiting weaknesses in buildings and boundary walls. The plant can be easily transferred to new locations by small fragments.

Under S.I. No. 477/2011 – European Communities (Birds and Natural Habitats) Regulations 2011, Regulation 49(2) any person who plants, disperses, allows or causes to disperse, spreads or otherwise causes to grow Japanese knotweed or any of the other invasive plants listed in Part 1 of the Third Schedule shall be guilty of an offence. Furthermore, Sections 52(7) and (8) of the Wildlife Act, 1976, as amended,1 make it an offence to plant or otherwise cause to grow in a wild state exotic species of plants.

Japanese Knotweed - a Building Surveyors perspective Img02

During a recent structural survey, we identified a cluster of Japanese knotweed in the early growth stage as illustrated in the above photographs. The location was a city centre site comprising of properties with small gardens in close proximity to each other therefore the risk that the plant had spread and affected other properties was  high. Treatment and removal costs were likely to be significant. Following advice from the Building Surveyor, our Client withdrew from the purchase given the risk and cost involved in dealing with this problem.

It is important that awareness is raised regarding the proliferation of this plant and the potentially serious consequences for homeowners.

Please see this useful link on Waterford County Councils website:

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