McCarthy & Stone is well known for having built some two thirds of the UK’s retirement homes, and has done so while also establishing a reputation for quality and integrity.

Its newest retirement living complex in the south west is on the site of a former country pub in Gloucester Road, Bath, located on the edge of the beautiful spa city.

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Challenge from an invader

Unfortunately, a clump of Japanese knotweed was growing adjacent to the narrow stream that forms the western boundary of the site.

While currently small, knotweed is a notoriously rampant invasive species that can completely blanket its immediate environment with dense and persistent canes. Its rhizome (root/energy storage system) will seek out and follow sources of moisture, and in so doing could penetrate the new development’s drains and sewers as well as enter the stream which would spread the infestation downstream.

Worryingly for developers, if not controlled, knotweed can also exploit weaknesses in concrete, tarmac and brick, and, in extreme cases can undermine the integrity of even large structures.

While it is not illegal to have knotweed on your site, existing legislation, along with public and lender perception and best practice, does provide a moral and reputational imperative to control it. Because the plant can lie dormant for a decade or more after being sprayed off before re-emerging, and because a new plant can grow from even a tiny piece of the parent rhizome, eradication can never be fully guaranteed; this makes the management obligation an ongoing – and potentially costly - commitment.

It’s no surprise, then, that many developers and site vendors dread – even hide – the discovery of knotweed on their site. However, true to its reputation, McCarthy & Stone chose instead to tackle the issue head-on, and turned to the experts from JP Associates (JPA) for best practice advice.

JPA’s director Jeremy Peirce is one of a few qualified amenity agronomists with a specialism in invasive and injurious weeds, and is a full member of the BASIS professional register, giving him a comprehensive understanding of the application of herbicides and their use in controlling knotweed.

Robust management is key

JPA began by undertaking a site survey and producing a comprehensive method statement covering both the demolition and construction phases of the project. This method statement included recommendations for an ongoing herbicide application programme to control the growth, the steps needed to manage any arisings from inside the contaminated area, and how to mitigate against the risk of any future re-growth.

It also provided strict controls for managing the contaminated site, including barriers to prevent accidental movement of potentially contaminated material, and washing of any equipment that came into contact with it.

To ensure that these critical measures were followed correctly, JPA not only oversaw key stages of the programme, but provided the ground crew with a ‘Toolbox Talk’ on identifying knotweed and how the method statement should be implemented correctly.

Jeremy said, ‘It’s all very well the executives and technical managers knowing the method statement for managing knotweed, but McCarthy & Stone has rightly recognised that it’s the team on the ground who can make the difference between whether it becomes a significant problem in the future or not.’

Once the initial soft strip was completed, JPA returned to the site to oversee the lifting of some footings located inside the potentially contaminated area to ensure that the ground crew was complying with the method statement.

He also liaised with the project engineer over the technicalities of installing an interception drain. This was needed to prevent site run-off water entering the stream, but the drain ran through the contaminated area, so Jeremy supervised the groundworks to ensure that no rhizome was in the dig zone.

All according to plan

The decision to engage an expert at the outset and work closely with him throughout the project, has saved McCarthy & Stone time and money.

Patrick Cunningham, pre-contracts manager at McCarthy & Stone's south west region, said, ‘By working with JP Associates closely throughout this project, we were able to find a straightforward, cost-effective solution to what could easily have become a difficult and costly issue.

‘Most importantly, we have been able to maintain our construction schedule, and with JPA’s education and oversight we know we’ve been doing things correctly throughout. That means we’ll be able to get the nod for adherence to our method statement without a glitch and gain that all-important planning sign-off.’