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Read this BEFORE you buy a site to build a house in the UK

Updated: Feb 25

Self building a house in the UK is extremely challenging

I have been a self employed Architect in the UK since 2009, focusing exclusively on private, domestic clients most of whom want to alter their existing homes. Occasionally I get asked to look at sites for one-off houses. If you are thinking of buying a site to build a house, this post has a number of things you should consider prior to purchasing the land.

Before we begin I should say this is not intended to be comprehensive, these are just a few of the things which can kill a development. This advise is based on my own experience in the UK and doesn’t apply to other countries. You should always consult a local Architect and your lawyer prior to purchasing land.

The first thing to say is that buying a site to build a house can be risky. What might seem like a plot with everything going for it may be impossible to develop, which can be a very expensive mistake if you paid for the land up front. Keep in mind that professional property developers don't pay up front, they do a deal with the land owner which is subject to planning approval. The money only changes hands on the day the planners grant permission. This kind of deal is seldom happens for small plots of land.

Outline Planning Permission

If you are considering a site which is being sold with planning permission, keep in mind this comes in two flavours; Full planning consent and Outline planning consent.

Outline consent is easier to archive, it just confirms that development is possible in principle. An outline planning application may not have detailed drawings of the house and often doest resolve major issues of access, drainage, overlooking, overshadowing, the style of building or its precise size and location on the site.

If you buy a site with outline planning consent you will still need to apply for full planning consent and you many not get it.

Do not assume that outline content gives a plot an advantage in gaining full planning consent. It is quite possible the outline consent comes with conditions attached by the planners which aren’t possible to satisfy in the subsequent full application.

Visibility Splays.

Every new house must be able to safely access the public road. The operative word here is “safely” and the design of any new junction with the public road will be assessed by the roads department of the local authority during the full planning application process. This may sound like a dull bureaucratic exercise but it has the potential to kill any development dead.

One of the aspect of road junction design which regularly causes huge problems is the visibility splay. Any new junction must be designed so the driver of a car trying to join the public road has an unobstructed view on either side. The higher the speed limit on that public road, the further up and down that road the driver must be able to see.

This all makes sense and sounds fair, so how can it kill off a development?

As part of your full planning application a pair of triangles must be shown on a drawing on either side of the proposed junction. The short side of the triangle will be 4.5m back from the public road. The length of the triangle is determined by the speed limit on that road, the higher the speed limit, the longer the triangle. The important thing to understand is that nothing inside the triangles can be more than 1 meter tall.

For a typical country road, where the national speed limit is 60 miles per hour, the visibility splay must extend, unobstructed, for 215 meters either side of the proposed junction, an overall length of 430 meters. That is huge and it almost guarantees the visibility splay will extend far beyond the boundary of a typical plot and cross into someone else's land.

visibility splay for a self build house UK
The 215m long visibility splay is in yellow, it measures 4.5m back from the road

Now, what happens if there is a wall or tree or other obstacle, more than 1m tall, inside the triangle but on the neighbours land? The short answer is that unless you can persuade that neighbours to remove the obstacle, no new junction will be approved.

No new road junction means no new house. The development is dead in the water. It’s that simple.

So, before you agree to buy a site have a professional check that the visibility splay can be achieved without impacting the neighbours property.

I’ve had people ask if convex mirrors, the kind commonly seen in the British countryside, could solve the problem. The simple answer is no, these are not supported by the Road Traffic Act.

Visibly Splays must also be demonstrated if your site uses an existing private road to join the public road. This can cause people to feel unfairly treated by the planners but the reason is simple, public safety. There are thousands of rural properties around the UK which pre-date the motor car and have farm lanes which join the public road. All this is fine until the farmer tries to sell of some land or a steading, to create new houses. New houses mean more cars using that farm lane to join the pubic road, more cars at that junctions increase the risk of a collision, especially if the driver cant see oncoming traffic.

You don't get to build a new house at the expense of public safety.

Ransom Strips

These are perfectly legal but, in my view, morally dubious and even professional property developers get caught out but them.

So you bought a site and you even got full planning permission for your new junction with the public road, well done. You own the site and the local authority owns the road but who owns the grass verge between the road and your site.

ransom strips UK
This is a possible ransom strip

Allow me to introduce your friendly local gagster. He bought that grass verge from the farmer years ago for a modest sum, in fact he owns hundreds of strips of grass all over the country. He’s a patient man and its finally paid off. He knocks on your door and tells you to pay him £100k otherwise he wont allow you to cross his property to access the public road. It tuns out you are landlocked and have no option but to sell up or pay up, hence, ransom strip.

If you are thinking of buying a plot of land have your lawyer double check the ownership extends right up to the public road. That unloved piece of grass between the fence and the kerb might look innocent but it could cost you very dearly.

Septic Tanks

Nobody likes to think about sewage, its out of sight, out of mind. But if you are considering about a small plot of land in the country, it wont have access to the public drainage system, so you will have to install a septic tank. You might think, well its buried in the ground how much trouble could it be. It turns out the regulations on where you can locate a septic tank can be impossible to satisfy on small plots of land.

The size of the tank is determined by the number of bedrooms in the house. The more bedrooms the more people, the more people them more, (flush)

To avoid contamination or damage to your home from raw sewage, the tank must be located at least 5m from the house and also 5m from any boundary with your neighbours. This includes agricultural hedges and fences. They might be fields now but someone could build a house there in the future and we cant have raw sewage seeping into their home.

septic tanks UK
Always check you have enough space to comply with septic tank rules

The tank also has to be accessible by a driveway or road which can carry a vehicle weightier at least 14 tonnes, for “de-sludging”, yes, that is every bit as disgusting as you imagine. This means that if you plan to locate the septic tank behind your rear house, there must be space for that 14 tonne vehicle to drive around the house.

On small or narrow plots of land these requirements may not be feasible or so little of the land is left for development that a house just isn't feasible.

This is a link to a design guide for septic tanks.



At first glance these issues may seem trivial but if you don't consider them up-front, before buying a site, you might waste a huge amount of money buying land which can never be developed

Remember, these are just some of the things which can stop a development for going ahead. If you are thinking about buying a site to build a house you can book a consultation with me to discuss options.


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