Japanese knotweed, dry rot and your home insurance

What is Japanese knotweed? 

Japanese knotweed (Fallopia japonica) is a fast-growing, invasive plant species that originates from eastern Asia. It was introduced to the UK in the 1840s as an ornamental plant and to feed cattle. But its rapid growth soon caused widespread problems.  

Why is Japanese knotweed a problem? 

Japanese knotweed is a perennial plant, meaning it lives for several years. It also grows quickly, sometimes up to 10cm each day. It can reach over two or three metres tall in a few weeks.  

Its roots can spread to seven metres in all directions and break through hard surfaces like property foundations, roads or walls. This can cause structural damage and even spread to your neighbours’ properties. 

Japanese knotweed has no natural predators in the UK, meaning it’s difficult to control. Because of this, it’s estimated that Japanese knotweed damage, management and removal costs the UK millions each year. For that reason, it’s illegal to introduce Japanese knotweed into the wild.  

What does Japanese knotweed look like? 

Japanese knotweed identification is crucial. Here’s what to look for: 

• Small, red-green shoots, similar to asparagus 
• Bamboo-like stems which are noticeably hollow and easy to snap 
• Green, heart-shaped leaves 
• Clusters of small, white flowers sprouting in summer 
• Brown and brittle stems once the leaves have died back in autumn 

It can be easy to confuse Japanese knotweed with other plants. If you’re unsure, you can send a photo to the Royal Horticultural Society. 

What is the law around Japanese knotweed? 

• If you have Japanese knotweed on your property: It's not illegal to have Japanese knotweed on your property. But you must stop it from spreading. If you don't and it spreads to your neighbours’ gardens, they could sue you under private nuisance laws 
• If you’re selling your home: If you know there’s Japanese knotweed on your property, it’s a legal requirement to declare it. If you’re unaware of the plant’s presence, the buyers’ conveyancing survey should pick this up. Either way, you might have to remove the Japanese knotweed before continuing the sale 
• If you’re buying a home: If there's Japanese knotweed on a property you want to buy, your mortgage provider will usually ask for a removal plan as part of your mortgage agreement. Your surveyor can advise on what action is needed and how to negotiate whether it will become your responsibility or must be removed before the sale 

How can I remove Japanese knotweed? 

If you find Japanese knotweed on your property, you need to take action straight away.  

Getting rid of knotweed is no easy task. As the roots can grow one meter deep, they can be very difficult to dig out. And if you leave even one centimetre of root in the soil, it will be enough to grow into a new plant. That’s why it’s always best to hire a professional.  You can find companies who specialise in treating and removing knotweed through the Trade Body for Invasive Species Experts or the Property Care Association. 

Removing knotweed usually involves spraying or injecting stems with chemicals. The plant will have to be resprayed several times, and treatment can take at least three years. 

Check the GOV.UK website for more information about removing Japanese knotweed. 

What is dry rot and why is it a problem? 

Dry rot (Serpula lacrymans) is a type of fungus that feeds off the moisture found in wood and timber. As a result, the timber becomes ‘infected’ and eventually starts to crumble, destroying materials that were previously considered safe. If it’s left unchecked, it could quickly spread and affect the structural stability of your home, causing long-term problems. 

Dry rot could also have an impact on your family’s health. Spores can affect people with breathing problems, and older people and babies can be particularly vulnerable.  

What are the signs of dry rot? 

Some potential signs of dry rot may include: 

• White, cotton wool-like growth, followed by a mushroom-coloured skin over wood surface 
• Cracking, splitting, shrinking or darkening of wood 
• Musty, damp, mushroom smell 
• Rust-coloured dust spores 

These signs might suggest dry rot, but they could also be caused by other problems. But if you notice any of these things, it’s always best to call in an expert. They’ll be able to help pinpoint the exact issue. 

What causes dry rot? 

Dry rot spores are always around, but they only grow in damp conditions. In other words, when wood gets wet and stays wet, it creates the perfect environment for the fungus to grow and spread. 

Common causes include: 

• Condensation, usually from poor insulation or heating 

• Poor ventilation, typically in areas like basements or attics 

• Penetrating damp, such as rainwater leaking through brickwork or a damaged roof 

• Rising damp or moisture from the ground rising through the masonry

• Plumbing leaks, such leaking showers, washing machines or damaged pipes  

Finding and treating the source of the problem can help prevent dry rot in your home. Take time to regularly inspect your home, repair any faults quickly and make sure that rooms are ventilated properly. 

How might dry rot affect the value of my home? 

Dry rot can weaken the structure of buildings, which causes instability and potential collapse. For that reason, it could affect the value of a property which could be a problem if you’re buying or selling. 

• If you’re selling your home: You must tell potential buyers about any dry rot. Surveyors will find it anyway, and buyers might not get a mortgage because of it. It’s best to treat dry rot before you sell 

• If you’re buying a home: Before buying a house, make sure you get a survey done on any property where your offer is accepted. If dry rot is found, you can decide whether to go ahead with the purchase. But remember, your mortgage lender might withdraw their offer 

How do you treat dry rot? 

You might be able to manage small cases of dry rot yourself. For example, you could remove any sources of moisture, like repairing a leak, and replacing any affected wood. 

But for best results, you should always contact a specialist. They can send a surveyor to inspect your home and check if any other areas of your home might be at risk of dry rot. They’ll then give you a full report and advise you on what to do next. 

The surveyor will then treat the dry rot. This involves: 

• Stopping the source of the moisture 

• Removing the damaged area 

• Treating the dry rot 

• Replacing any timber