Dr Samuel Hughes is Director of Housing at the Centre for Policy Studies.
In a free country, the Government does not control every aspect of people’s lives. It lets people decide for themselves how to live, only limiting their actions to stop them harming others: John Stuart Mill’s ‘harm principle’. We might support the harm principle because we think respecting people’s autonomy is intrinsically important, because we think government committees tend to be incompetent at making choices for us. It has been fundamental to how the British people have understood government’s role for centuries.
Lots of building regulations are consistent with the harm principle. Many of the oldest ones were aimed at preventing fires: a thatched roof is a risk not only to its owner but to neighbours and the entire city. That is why they have been de jure banned since the Middle Ages – in London since 1212. Another standard kind of building regulation prevents buildings that are defective in invisible ways: I haven’t consented to faulty construction that I didn’t know about.
Unfortunately, Britain has recently seen a raft of regulations that are hard to justify against these principles. I have just brought out a report for the Centre for Policy Studies investigating some of these. Many are in something called Approved Document O, introduced in 2022, which deals with the risk of overheating. Section 1 of this document sets out a ‘simplified method’ to show that buildings will not overheat
. According to this regulation, the maximum window area of a building is fixed at between 11 per cent and 18 per cent of its floor area, depending on location and orientation. A typical detached Georgian house has windows that are about 33 per cent of its floorspace. So it would have to block up between a half and two-thirds of its windows to comply. Terraces have less glazing, but will still often surpass the Part O Section 1 limits.
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This house has a glazing ratio of around 33 per cent; to comply with Part O §1.1, it would need to have between half or two-thirds of its windows blocked up.
The same section also requires that all windows be at least 55 per cent openable – 70 per cent in London. Sash windows can never be more than 50 per cent open. So Part O Section 1 actually bans sash windows – the most popular window type in Britain for the last three centuries.
This sash window falls well below Part O §1.7 rules on openable area.
That sash windows can only be partly opened is not a secret: everyone who buys a house with sash windows is aware of this. Nor is it a secret that a house with large windows will become warmer on sunny days than a house with small ones. The British people have been aware of the downsides of big sash windows for as long as they have systematically preferred them against all the available alternatives. So why should a liberal government stop them from doing this? They have harmed nobody except – at most – themselves thereby. If they want large sash windows rather than small hinged windows, that is a choice that the public can make themselves.
It is true that Part O Section 2 sets out an alternative to the ‘simplified method’: ‘dynamic thermal modelling’. This allows developers to prove that they have put in air-conditioning to prevent overheating, and that they should be allowed to have larger windows. But this modelling is expensive, complicated, and time-consuming. It is unclear whether it will work for cheaper housing and small builders. If the ‘simplified method’ has any reason to exist at all, it must be that it is cheaper. So there is a real risk that large sash windows have just been banned for those on lower incomes.
Other new regulations do not even have this partial escape clause. As of 2022, all new windows must have a sill or guard height of 1100mm (‘guards’ are metal bars). This will tend to generate small, squat windows, set too high up the wall for inhabitants to look out of them when they are seated. The regulation is justified as a measure to stop people falling out. This seems strange. Georgian and Victorian window sills are sometimes floor height, and almost always far below 1100mm.
The same has been confirmed across Europe, for as long as large-glazed windows have been easily produced. Everyone knows that they might fall out of them under certain unlikely circumstances. They take that risk because they want large windows with a nice view. For centuried, this is the trade-off that most have chosen. Is it really a good idea for ministers to make a different trade-off for them?
The low sills and absent guards of these windows would violate Part O §3.9. They are probably too large for §1.1, and certainly blocked by §1.7 for being sash windows.
A fourth offending regulation is the heat retention standards, contained in a document called Approved Document L. Unlike overheating, heat retention is a reasonable thing for the Government to regulate for. Poorly insulated buildings consume more energy, generate more greenhouse gas emissions, and thus harm people other than the buildings’ inhabitants. However, we should give people as much flexibility as possible in how they reach these standards: provided people get a given level of heat retention, the Government should not mind how they do this.
Unfortunately, this is not currently the case. Part L sets heat retention standards for every element of a building – walls, windows, roofs, and more. This makes some traditional building elements almost impossible. For example, dormer windows have two very small ‘walls’ on either side, filling the triangular spaces between the main roof and the projecting roof of the dormer. It is almost impossible to make these as thick as the main walls of the building, so they normally fail Part L standards. Traditional dormers are thus virtually banned and are likely to be formally so as standards rise.
There is an easy way around this: set an alternative ‘whole building heat retention standard’, letting people have dormers if they compensate for them with thicker walls or more roof insulation. This comes at no cost to the environment: the same result is achieved, just in a different way. But Part L does not make provision for this.
These dormers would probably be banned under Part L. Needless to say, the remaining windows infringe rules on openable area, sill height, and potentially also overall size.
So large windows, sash windows, floor-length windows and dormers are on the way out, at least at the lower end of the market. Obviously, the Government did not intend to do this: the new building regulations were prepared by officials and slipped past ministers with these features unnoticed.
But now that the problems have been pointed out, swift action is required. Part O must be completely reviewed. There is a serious case for scrapping it: it is unclear that a liberal state should remove choices about window size and form from its people. Failing that, it should be rewritten to relegalise Britain’s standard popular window types. Part L also needs to be reviewed to stop it from banning dormers out of sheer rigidity.
Window regulations seem like an obscure and technical topic. It is probably because of this that these peculiar rules were able to pass through a long consultation process without a fuss. But they matter. ‘Architecture is windows’, it is said, and these rules threaten to give England a generation of houses that are uglier and less popular than those we have built historically.
The homebuyers and renters of England are responsible adults. They have proven themselves competent to choose what sort of windows they want. If we don’t trust them to do this, what will we trust them with?
Dr Samuel Hughes is Director of Housing at the Centre for Policy Studies.
In a free country, the Government does not control every aspect of people’s lives. It lets people decide for themselves how to live, only limiting their actions to stop them harming others: John Stuart Mill’s ‘harm principle’. We might support the harm principle because we think respecting people’s autonomy is intrinsically important, because we think government committees tend to be incompetent at making choices for us. It has been fundamental to how the British people have understood government’s role for centuries.
Lots of building regulations are consistent with the harm principle. Many of the oldest ones were aimed at preventing fires: a thatched roof is a risk not only to its owner but to neighbours and the entire city. That is why they have been de jure banned since the Middle Ages – in London since 1212. Another standard kind of building regulation prevents buildings that are defective in invisible ways: I haven’t consented to faulty construction that I didn’t know about.
Unfortunately, Britain has recently seen a raft of regulations that are hard to justify against these principles. I have just brought out a report for the Centre for Policy Studies investigating some of these. Many are in something called Approved Document O, introduced in 2022, which deals with the risk of overheating. Section 1 of this document sets out a ‘simplified method’ to show that buildings will not overheat
. According to this regulation, the maximum window area of a building is fixed at between 11 per cent and 18 per cent of its floor area, depending on location and orientation. A typical detached Georgian house has windows that are about 33 per cent of its floorspace. So it would have to block up between a half and two-thirds of its windows to comply. Terraces have less glazing, but will still often surpass the Part O Section 1 limits.
This house has a glazing ratio of around 33 per cent; to comply with Part O §1.1, it would need to have between half or two-thirds of its windows blocked up.
The same section also requires that all windows be at least 55 per cent openable – 70 per cent in London. Sash windows can never be more than 50 per cent open. So Part O Section 1 actually bans sash windows – the most popular window type in Britain for the last three centuries.
This sash window falls well below Part O §1.7 rules on openable area.
That sash windows can only be partly opened is not a secret: everyone who buys a house with sash windows is aware of this. Nor is it a secret that a house with large windows will become warmer on sunny days than a house with small ones. The British people have been aware of the downsides of big sash windows for as long as they have systematically preferred them against all the available alternatives. So why should a liberal government stop them from doing this? They have harmed nobody except – at most – themselves thereby. If they want large sash windows rather than small hinged windows, that is a choice that the public can make themselves.
It is true that Part O Section 2 sets out an alternative to the ‘simplified method’: ‘dynamic thermal modelling’. This allows developers to prove that they have put in air-conditioning to prevent overheating, and that they should be allowed to have larger windows. But this modelling is expensive, complicated, and time-consuming. It is unclear whether it will work for cheaper housing and small builders. If the ‘simplified method’ has any reason to exist at all, it must be that it is cheaper. So there is a real risk that large sash windows have just been banned for those on lower incomes.
Other new regulations do not even have this partial escape clause. As of 2022, all new windows must have a sill or guard height of 1100mm (‘guards’ are metal bars). This will tend to generate small, squat windows, set too high up the wall for inhabitants to look out of them when they are seated. The regulation is justified as a measure to stop people falling out. This seems strange. Georgian and Victorian window sills are sometimes floor height, and almost always far below 1100mm.
The same has been confirmed across Europe, for as long as large-glazed windows have been easily produced. Everyone knows that they might fall out of them under certain unlikely circumstances. They take that risk because they want large windows with a nice view. For centuried, this is the trade-off that most have chosen. Is it really a good idea for ministers to make a different trade-off for them?
The low sills and absent guards of these windows would violate Part O §3.9. They are probably too large for §1.1, and certainly blocked by §1.7 for being sash windows.
A fourth offending regulation is the heat retention standards, contained in a document called Approved Document L. Unlike overheating, heat retention is a reasonable thing for the Government to regulate for. Poorly insulated buildings consume more energy, generate more greenhouse gas emissions, and thus harm people other than the buildings’ inhabitants. However, we should give people as much flexibility as possible in how they reach these standards: provided people get a given level of heat retention, the Government should not mind how they do this.
Unfortunately, this is not currently the case. Part L sets heat retention standards for every element of a building – walls, windows, roofs, and more. This makes some traditional building elements almost impossible. For example, dormer windows have two very small ‘walls’ on either side, filling the triangular spaces between the main roof and the projecting roof of the dormer. It is almost impossible to make these as thick as the main walls of the building, so they normally fail Part L standards. Traditional dormers are thus virtually banned and are likely to be formally so as standards rise.
There is an easy way around this: set an alternative ‘whole building heat retention standard’, letting people have dormers if they compensate for them with thicker walls or more roof insulation. This comes at no cost to the environment: the same result is achieved, just in a different way. But Part L does not make provision for this.
These dormers would probably be banned under Part L. Needless to say, the remaining windows infringe rules on openable area, sill height, and potentially also overall size.
So large windows, sash windows, floor-length windows and dormers are on the way out, at least at the lower end of the market. Obviously, the Government did not intend to do this: the new building regulations were prepared by officials and slipped past ministers with these features unnoticed.
But now that the problems have been pointed out, swift action is required. Part O must be completely reviewed. There is a serious case for scrapping it: it is unclear that a liberal state should remove choices about window size and form from its people. Failing that, it should be rewritten to relegalise Britain’s standard popular window types. Part L also needs to be reviewed to stop it from banning dormers out of sheer rigidity.
Window regulations seem like an obscure and technical topic. It is probably because of this that these peculiar rules were able to pass through a long consultation process without a fuss. But they matter. ‘Architecture is windows’, it is said, and these rules threaten to give England a generation of houses that are uglier and less popular than those we have built historically.
The homebuyers and renters of England are responsible adults. They have proven themselves competent to choose what sort of windows they want. If we don’t trust them to do this, what will we trust them with?