This article is not about the building decaying. It is about being held responsible for what other people do.

Five things that happen

Entry and occupation

A broken lock, a smashed window, a back door that gives. People come in through those and use the house. Once somebody has settled, removing them takes time and money, and it is not something managed remotely from another country.

Metal theft

Easy to overlook and very common. The targets are not only the contents: the outdoor unit of an air conditioner, copper wiring and pipe, aluminium window frames, the water heater and its fittings.

The theft is not the problem. The damage done to reach it is. Walls are opened to pull out wiring. Pipes are cut and then leak. A window with its frame gone stays open to weather. The metal might be worth tens of thousands of yen; the damage is an order of magnitude more. And the opening left behind is an invitation to whoever comes next.

Illegal dumping

A site that looks unmanaged attracts bulky waste, household rubbish, sometimes commercial waste. Once one item has been left, the location is read as a place where dumping is tolerated, and it accelerates.

The difficulty is that the cost of clearing dumped waste tends in practice to end up with the landowner. Where the person who dumped it cannot be identified, you are the only party available.

Use as a base

A building that is unoccupied, has no power connected and receives no visitors suits certain purposes. Vacant properties have been used as bases for telephone fraud and to store stolen or dangerous goods. Even where the owner knew nothing, the property becomes the subject of an investigation.

Arson

The most serious. Dry garden trees, abandoned rubbish, piled dead leaves, dumped combustibles. These are literally kindling, and an unoccupied building means the fire is found late.

In Japan's dense timber neighbourhoods, fire reaches the house next door. At that point this stops being a question about property and becomes a question about law.

A Japanese rule that surprises foreign owners

Japan has legislation, dating from the Meiji era, on liability for fire caused by negligence. In one sentence: if you accidentally burn down your neighbour's house, you generally bear no liability to compensate them unless you were grossly negligent.

The reasoning was practical. Where timber buildings stood packed together and fire spread readily, a single lapse could otherwise destroy a person's life. It differs considerably from what most Western buyers expect, and it is usually received as good news.

The condition attached to it is where the attention belongs. Where there was gross negligence, the protection does not apply.

Gross negligence broadly describes a state where the outcome could have been foreseen and avoided with slight care, and care was markedly absent. Whether it exists is decided on the facts of the case. But a vacant house left unlocked and open to anyone for a long period, or a building left in place despite a warning about its electrical condition, moves the assessment of the owner's conduct in an unhelpful direction.

So the sequence runs like this. The house is left unmanaged. Somebody enters and sets a fire. The fire spreads next door. How the property was being managed is examined. The protection may not extend to you. You compensate the neighbour.

And the insurance may not be there either

In the same scenario, the other support can be missing as well.

Fire insurance carries a duty to state the facts accurately at the outset and to notify the insurer when the building's use changes during the policy. A building insured as a residence that becomes vacant, without the insurer being told, represents an increase in risk that can lead to the contract being cancelled and the claim going unpaid.

In the worst case, three things happen together. You compensate the neighbour. Nothing is paid on your own building. And clearing the burnt remains is also at your expense. Years of premiums do not alter any of it. How the classification and the disclosure duties work is worth confirming once, in advance.

The defence is a record of having managed it

Turn all of the above around and the direction is clear. Keep managing the property, and keep evidence that you did. The first deters the events themselves. The second is what you have to show if the worst happens anyway.

The same list, almost item for item, is what keeps a property out of the category that costs you the residential land tax reduction. That process is set out in why Japan's empty houses are not demolished.

The neighbour notices first

A broken window. An unfamiliar car parked outside. Rubbish accumulating in the garden. The person who sees these first is, almost always, the one living next door.

The question is whether that person can reach you.

• Does the neighbour know who owns the house?
• Do they have contact details?
• Are those details in Japan?
• Can the person at the other end be spoken to in Japanese?

Where all four are no, the neighbour has two options: contact the authority, or give up. And contact with the authority accumulates as a record that the property is poorly managed.

Put a single point of contact in Japan and the whole picture changes. The neighbour gains somebody to call, and you gain an early warning system that costs nothing to run.

If you are looking at a long-empty property

On a property that has stood vacant for years, it is not unusual to find existing signs of entry, metal fittings already stripped out, or waste left on the grounds. All of it becomes yours on completion, along with whatever relationship the previous owner had with the neighbours.

Those are on-site questions. What can be established from records before you travel, and what cannot, is set out in what you must verify yourself before buying.