Why do we value a basement flat less than the flat above it?

By Joshua Platt BSc (Hons) MRICS

Walk into any estate agent and ask why the basement flat is cheaper than the identical flat one floor up. You will not hear about worktops, or taps, or smart thermostats. You will hear one word. Light.

The rooms are the same size. The postcode is the same. The service charge is the same. The only real difference is that one home gets daylight and the other does not, and the market prices that gap at tens of thousands of pounds.

That ordinary fact carries a lesson developers would rather you missed. If light has a clear cash value when you buy a home, it has a clear cash value when a new building takes it away. The right to light is one of the oldest property rights we have, recognised in English law for almost two hundred years. The problem is not the right. The problem is that the way we measure "enough" light, and the way developers are sometimes allowed to pay for removing it, belong to a different century.

In short:

• The price gap between a basement and a ground floor flat proves daylight has a measurable, cash value, and the right to light exists to protect it.
• The test for whether a room has "enough" light still rests on a benchmark set in the 1920s that research suggests was never scientifically proven.
• A developer can sometimes turn your power to stop a build into a modest compensation payment, so understanding how the loss is valued is the difference between fair money and far too little.

Why is a basement flat worth less than the flat above it?

Because daylight is doing more work in that price than people admit. Damp, security and outlook all feed in, but light is the single biggest driver. You can renovate a kitchen. You can replace the windows. You cannot order more natural daylight, and you cannot install a brighter sun. A home either has light or it does not, and buyers feel the difference the moment they walk in.

What the market is really pricing is the absence of light. The right to light is the legal version of the same instinct. It accepts that daylight reaching your windows is worth money, and that taking it has a cost somebody should pay.

What does the law actually mean by your "right to light"?

A right to light is not a right to all of your light. In the leading case, Colls v Home and Colonial Stores (1904), the court held that you are entitled to "sufficient light according to the ordinary notions of mankind." That means enough for the ordinary use of the room, not every ray you currently enjoy.

Most rights to light are never written into a deed. They build up quietly. Roughly twenty years of continuous daylight through a window can create a legal right under section 3 of the Prescription Act 1832. You do not have to register it. You do not have to ask. It simply accrues over time.

So the right is real, and it is yours. Every dispute then turns on one slippery word. How much light is "enough"? That is where developers and homeowners stop agreeing.

Is the way we measure light loss stuck in the past?

Here is the part developers rarely volunteer. The benchmark surveyors still use to decide whether a room has "enough" daylight was set by an engineer named Percy Waldram in the 1920s.

Waldram's standard treats a point in a room as adequately lit if it receives a "sky factor" of 0.2 per cent, which is roughly 10 lux, or one old foot-candle. By convention, a room passes if that level reaches at least half of its floor area. He called the threshold the "grumble point," the level below which he reckoned an ordinary person would start to complain.

The trouble is that the figure looks close to a guess. Research by Chynoweth at the University of Salford, analysing the historical archives, found no evidence that 0.2 per cent was ever based on a real study of how people perceive light. It appears to have started as a rule of thumb and been justified afterwards. Controlled experiments since have suggested that people actually need more than double that level for comfortable everyday use.

Now think about how much has changed since the 1920s. We work from home. We spend far more time indoors. We understand far more about sleep, wellbeing and mental health, and about how our surroundings shape them. Yet in many cases the benchmark for "adequate light" is still anchored to assumptions from the age of gaslight. A low bar matters, because the lower the threshold, the more of your light can be taken before the law treats it as a real loss. That means smaller claims, weaker leverage, and cheaper buy-offs for the developer.

Why doesn't anyone search Rightmove for a "0.2 per cent sky factor"?

Because instinctively we all measure light the way the market does, not the way a 1920s diagram does. Nobody filters homes by lumens. Nobody searches for a sky factor. They search for "bright." They search for "south facing." They search for "flooded with natural light," and "light and airy."

Estate agents lead with those words because they sell. Buyers pay premiums for them. Tenants seek them out. Families build their shortlist around them. The market worked out a long time ago that light creates value, and it has never needed a surveyor's formula to prove it. The law is not inventing something strange. It is recognising what every property brochure in the country already says.

Why is light becoming more valuable, not less?

Because it is becoming scarcer. Britain's cities are getting denser. Buildings are getting taller. Urban land is getting more valuable. There is only so much sky, and every window and every new floor competes for it. The scarcer something gets, the more it is usually worth.

There is one more thing that makes lost light different from almost every other downside of development. It is permanent. The noise, dust and disruption of a building site end when the scaffolding comes down. Lost light does not. It is gone for the entire life of the new building. That is exactly why the law treats it as a property right and not a passing nuisance.

Can a developer really just take your light away?

Not simply, and not usually for free. This is where worried owners are most often misled.

A developer who blocks your light without agreement risks an injunction, a court order that can, in the right case, force them to cut back or even remove part of what they have built. It has genuinely happened. To avoid that risk, a developer has three options. Agree a release with you. Persuade a court to award you damages instead of an injunction. Or, only where there is a connection to a public body, use section 203 of the Housing and Planning Act 2016 to override the right.

Section 203 does not delete your right. It converts your power to stop the build into a right to compensation. That sounds fair until you see how the compensation is worked out. It is based on "book value," and it can be reduced by "betterment," the argument that the new development raises local property values and therefore offsets your loss. In some cases that logic can push the figure close to nothing. Major London schemes, including the building known as the Walkie Talkie, 22 Bishopsgate and Tottenham Hotspur's stadium, have relied on these powers to get built.

So the honest answer is not that your light is unprotected. It is that the figure you are first offered may be a fraction of what the loss is really worth, calculated on rules designed to keep development moving rather than to make you whole. We set out how those powers work, and where they can be challenged, in our guide on whether developers can override your right to light, and how it played out for owners near a Sheffield scheme in this case study.

Why does losing light hit so hard?

Picture how most people come to own their home. Thirty years of mortgage payments. Overtime. Holidays skipped. A flat chosen, in part, because of the afternoon light in the living room. Then a development goes up next door, the bright room turns grey, and the compensation on the table reflects a 1920s formula rather than what was actually lost.

The financial hit is real, and so is the daily experience of living in a room that used to be full of light and now is not. Natural light is not a luxury. It regulates sleep, mood and the body clock, which is why darker homes are linked with conditions such as seasonal affective disorder.

And there is a simple fairness point underneath all of it. We compensate people when their land is taken. We compensate them when noise affects their home. We compensate them when infrastructure changes their surroundings. Light should not be the exception. The market already treats it as valuable. The law simply agrees.

What should you do if a development threatens your light?

Act early, and get the loss measured properly rather than accepting the developer's version of it.

• Check whether you have a right at all. Broadly, that means around twenty years of continuous light through the affected windows.
• Get an independent assessment of the loss. A developer's own daylight survey is written to protect the developer, not you.
• Find out whether section 203 is even available to them. It is not a free pass, and it cannot be used for a purely private redevelopment of land that has always been privately owned.
• Do not accept the first compensation figure. The opening offer is rarely the ceiling.

If a new build or extension is taking light from your home, the right to act is yours, but a right only matters when you use it. Start a claim and we will tell you, plainly, whether you have one worth pursuing.

This article is general information about rights of light in England and Wales, not legal advice on your circumstances. Daylight Protect is a litigation facilitator. We are not solicitors.