Is It Legal To Build a House Underground? Do You Need Planning Permission for a Basement?

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Is It Legal To Build a House Underground?

Do You Need Planning Permission for an Underground House?

Underground House

Is it illegal to build an underground house, basement, bunker, cellar or any type of underground room in your backyard? If it wasn’t illegal, you may as well as ask, is it legal to build a house above-grade or above the ground level? Building a house above or below grade requires a building permit obtained from the local authorities. It doesn’t matter whether you are building horizontally or vertically in any direction, you will need a building permit before proceeding with excavations. To start with, before digging any kind of hole, trench or pit on your residential lot, you are required to get permission from utility operators in your city or town. If the utility services in your area are managed and maintained by the local municipality, then you have to contact the municipality to come and locate the underground services on your residential lot. Unless all utility operators (water, sewer, gas, electricity, telecom etc.) have done an inspection on your private property and identified all underground services, you are not allowed to start digging or building any kind of structure.

As you can see, we already have two kinds of permits or permissions that you have to obtain before building an underground house or room. Depending on your location, development plans, building type and use, there are many other permits that you have to obtain under zoning laws and town planning regulations. You may not start building until you have obtained all the permits. So you are now aware of a building permit as well as a digging/excavation permission. There is a third group of municipal laws and regulations falling under planning permission.

What is the Difference Between a Building Permit and Planning Permission?

A building permit is the normal permit obtained from local authorities for designated /classified developments permitted under existing zoning laws, title deeds, land use and setback requirements. When a new town or city is established, the town planners sit down to divide and classify land for specific land uses e.g. residential, commercial and industrial areas. The zones are further sub-divided into sub-zones, for example, low class, middle class and high class residential areas. These sub-zones come with their own classified title deeds and setback requirements which set them apart from other zones. For example, low-income areas often have smaller lots (front and backyards) and therefore building external structures such as swimming pools may not be allowed.

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When you need to build something outside the existing blanket rules and regulations (zoning laws and title deeds), you must apply for a planning permission from the local authority. So whether you need a planning permission for building an underground room or basement depends on what’s allowed under permitted developments in your area. You must find out from the municipality or city council. In the USA, basements are usually built under a building permit as part of a new home. In the United Kingdom, whether an underground room requires a planning permission or not, depends on many factors for example, you have to ask yourself the following questions:

What is the size of basement and amount of excavations (earthworks) involved?

The gross floor area of your basement as well as its depth matters because it determines the volume and extent of excavations that need to be done on your Plot or Lot. Major earthworks exceeding the combined gross floor area of your house + 50% of the backyard will need a planning permission.

Most basements are single-storey underground structures. If your basement has two or more storeys (or more than 4 metres deep), you will need to get a planning permission. In this case, no additional floors can be built to an existing basement even if it was built under a permitted development permit.

Will the basement be a detached standalone structure or will it be attached to the main house?

If the proposed project is a basement extension, alterations and refurbishments that affect the structural and architectural elements of the building, a planning permission will not be needed but as always, you will need a building permit that ensures the alterations and additions are done in compliance with building codes. Alterations to electrical, mechanical and plumbing installations also require a permit, including newly installed systems.

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However, this will depend on your town, city or district council. Some cities may require planning permission for basement extensions. In most cases, a planning permission will be required if your basement is a detached standalone structure, but not needed when the extension is attached to the main house.

Will the construction of a basement alter the front and side elevations (interfere with the street view) of your house?

Most building codes in the USA and UK state that the street view of your house, which is usually the front elevation or front yard should be unobstructed. Any side facing the streets must have its architectural elevation or facade fully visible from the streets, to maintain the aesthetic market value of the suburb. Structures which change the appearance of the front elevation pose the risk of making your home as well as the neighbourhood unsightly. For this reason, structures like light wells, rails, septic tanks, shipping containers and water storage tanks must be positioned in the backyard. If a light well is to be built in front of the house, it should be unobstrusive, discreet, aesthetically pleasing and laid flush with the ground.

Do you live in a conservation area protected by the government?

Conservation areas are not just land marks or places of historical, archeological and architectural importance, but they also include areas of natural and ecological importance with protected species and habitats. It’s usually the obligation of government to protect such areas. Legislation is in place to prevent damage and destruction to such places by human activity and industrialization. Building is one of human activities that can cause damage to conservation areas. For this reason, if your proposed developments or renovations are located in a conservation area, you will need to apply for planning permission. In conservation areas, there are no permitted developments, a planning permission is the first thing you need to get before being approved for a building permit.

Do you live in a multi-family unit, for example, an apartment block, condominium or cluster-units?

Multi-family residential units are found in apartments, flats, condos and semi-detached cluster home housing. If you bought a household unit in social housing blocks or communities like the ones mentioned previously, the title deeds will prevent you from building extensions and additions, as well as making structural modifications to the dwelling. A planning permission will be needed, for example to build a basement / underground room.

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Do you live in a flood zone, critical drainage area or near a watercourse?

Basements and any underground rooms such as cellars are prone to flooding due to their floor position which is way below grade or flood base elevation (FBE). In the United Kingdom, a Flood Risk Assessment is required prior to approval or building a basement. There are high chances of your basement building proposal being rejected when it’s situated in a flood zone, critical drainage area or watercourse. In a case where your basement proposal is approved, you should have obtained planning permission which requires a detailed flood mitigation plan done by professional consulting engineers.


It’s illegal to build a basement or any underground house without a planning permission. An underground room or extension may not be built where a planning permission overrides a permit for permitted developments. Habitable underground rooms are also subject to basement building codes to ensure safety from risk of collapse, flooding, suffocation and fire hazards. A means of escape should be provided for in the event of emergencies. Doors and windows must not have complex operating mechanisms. They should be opened easily from the inside without requiring special knowledge. HVAC installations like boilers, radiators and hot water tanks must be located in their own room, separate and away from the living/sleeping area. Visit the following post for more detailed information on underground houses and basements.

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