Japanese knotweed and buying a flat, what first time buyers need to know

It's easy to think knotweed is a houses-with-gardens issue. You're buying the third floor of a block, so surely it's someone else's problem. Not quite.

Knotweed spreads underground through roots, called rhizomes, and it doesn't respect boundaries. It can be in the communal grounds, along a car park edge, beside bin stores, on a neighbouring plot, or on railway or council land next door. If it's close to the building, a lender's valuer will care, and so should you.

The other catch is that you may own very little of the land. In most flats you hold a lease on your home and share the common parts through the freeholder or a management company. So the plant might not be yours to treat, but it can still affect your ability to get a mortgage, and later to sell.

The TA6 is the Property Information Form the seller completes during conveyancing. It includes a question on Japanese knotweed. The seller usually has to say whether the property is affected, and if it is, give details of any treatment plan.

Two things to bear in mind for flats. First, the seller may only know about their own flat and not the wider block, so a clean answer isn't a guarantee. Second, the answer should be consistent with what the freeholder or managing agent says. Your solicitor can raise questions with the managing agent as part of the leasehold enquiries, and you should ask them to do exactly that.

Don't fudge your own side of this. If a seller ticks the wrong box, that's a problem for them, but you're the one who'll live with it. Ask directly, in writing, and keep the replies.

This depends on your lease, so read it, or have your solicitor read it and explain it in plain English. In many blocks the freeholder or management company looks after the grounds and recovers the cost through the service charge. That means treatment could land on every flat owner as a bill.

If the knotweed is on land belonging to someone else, such as a neighbour, the council or a rail operator, the picture gets messier. Responsibility can be harder to pin down and treatment may not be in your block's control at all.

Ask your solicitor to check whether there's a known infestation, whether any treatment has been planned or paid for, and whether a cost is likely to be passed on through the service charge. Laws and case outcomes around liability can change, so confirm anything specific with a solicitor rather than relying on a general guide.

Lenders look at risk to the property as security. Knotweed close to a building can worry them because it can affect the value and, in some cases, the structure. Each lender has its own policy, so there's no single rule, and what one declines another may accept with conditions.

A valuer who spots knotweed, or who's told about it, may flag it in the report. The lender might then refuse, ask for more information, or lend only if certain conditions are met. For a flat, they'll also want to understand where the plant is and who controls that land.

This is why the TA6 and the managing agent's replies matter. If the lender learns about knotweed late, you can lose weeks. Better to surface it early and decide whether to carry on before you've spent heavily on surveys and legal fees.

A professional management plan is often the thing that turns a flat 'no' into a conditional 'yes'. It's a documented programme of treatment, usually carried out by a specialist contractor, which sets out where the knotweed is, how it will be dealt with, and over what period.

For lenders, the useful bit is evidence. A credible plan shows the problem is known, assigned to someone competent, and being dealt with. Many lenders look more kindly on a property with a plan in place, particularly where the knotweed is some distance from the building. Some will still decline, and the outcome depends on the lender and the specifics.

What to ask for in a block:

1. 1A copy of the management plan and the contractor's name.
2. 2A site plan showing where the knotweed is in relation to the building.
3. 3Confirmation of who pays, and whether it comes out of the service charge.
4. 4Any guarantee or insurance backing the treatment, and how long it lasts.

A plan isn't a cure. Treatment can take several years, and you'd be buying into an ongoing process, not a finished one.

Check the seller's TA6 carefully and ask your solicitor to chase the managing agent for the block's position. Look around the site yourself on a viewing, including edges, fences, car parks and any wasteland nearby, and ask the agent directly if there's any knotweed on or next to the development.

Tell your mortgage broker early if there's any sign of it. They'll know which lenders are more flexible, and they can ask before you apply rather than after a failed valuation.

If there's a plan, read it. If there isn't and knotweed is confirmed, think hard about whether you're comfortable with the uncertainty. You can negotiate on price, ask for treatment to be completed first, or walk away. That's a perfectly sensible choice, and cheaper than inheriting someone else's headache.