Rampant Japanese knotweed undermining house values and a hidden cost to buyers

Invasive plant species can devalue properties substantially and cost home-owners tens of thousands of euro

The rampant spread of an invasive plant species is devaluing properties substantially and costing home owners tens of thousands of euro to remedy. Japanese knotweed can now be found "in every county in Ireland" and there is a chronic lack of awareness of the scale of the issue or its devastating effect, according to Dr Frances Giaquinto, a botanist and ecologist.

Addressing the annual conference of the Institute of Professional Auctioneers and Valuers (IPAV), Giaquinto called for clear guidelines on how to handle and address the invasive species. In the UK, estate agents are obliged to tell potential buyers where it is present on a site and a similar approach needs to be adopted here. Giaquinto recommended that mortgage providers should insist on a detailed land survey – as well as a building survey – before purchase.

The problem is not restricted to rural areas. Giaquinto said, she regularly sees cases in housing estates and has already visited “many infestations” in Dublin gardens this year.

Illegal growth

Properties most at risk include terraced houses with common boundaries, properties next to routes such as rivers, canals, Luas, rail and roads and abandoned or neglected properties. Under current EU law, while it is not illegal to have Japanese knotweed on a property, it is illegal to plant, disperse, allow or cause it to disperse or spread. Giaquinto told the conference that the onus is on all landlords – State and private – to prevent its dispersal. She says the risk of purchasing an infested property “is increasing at an alarming rate, even though it may not be obvious until after the purchase has been made”.


The problem is very expensive to tackle too, often costing between €30,000 and €40,000 to rid a property completely.

IPAV chief executive Pat Davitt said: "There is an onus upon the Government to undertake an awareness programme about the issue. Should the Government wish to introduce consumer protection legislation here, similar to that of the UK, IPAV would support it."