House extensions: how to transform a detached house

House extensions design: the complete guide with everything you need to know to produce house remodelling and conversion projects together with 3D model example ready for download

A house addition or remodel is an extension or modification to an existing house and a smart/efficient way to increase the living space in your house. An excellent way to create extra room for more modern life-style needs such as open-plan kitchen-diners, playrooms or even a home office area. This may include a second-storey addition, a dormer, a footprint expansion or simple interior reconfigurations. A house extension also implies the opportunity to rethink the existing house layout that works better for you and, at the same time, it can even be an opportunity to bring in more natural light.

If your existing home no longer meets your needs, building an extension is a wise investment and a good way to gain the extra space you may need.

When it comes to house extensions, there’s a lot that needs to be considered for a project to be successful. Our guide will cover in-depth information and fundamental design aspects that will definitely turn out to be useful for a well-designed house extension.

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Home additions: Construction Permit

To get more living space in your house you may consider an extension and adding one or two extra rooms will require appropriate planning permission. The following section will provide useful references to building regulations for both the U.K. and U.S.A.

Planning permission U.K.

Even if you don not need Planning Permission (because you are using permitted development rights), you must get a Building Regulations approval. The Building Regulations 2010 covers the construction and extension of buildings and sets out minimum requirements for general safety requirements, fire prevention, ventilation, structural integrity, energy efficiency etc.

To get your extension approved, you could either ask your local authorities Building Control Department or contact a local inspector that is totally independent from the council.

Typical Work examples that need Approval:

  • Loft conversions
  • External walls
  • Internal structural alterations such as removal of a load-bearing walls
  • Altered openings for new doors and windows
  • Roofs
  • Drainage and electrics

Planning permission may not be required for extensions or house additions as they are considered to be permitted developments, provided that:

  • extensions must not exceed 50% of the total area of land around the original house
  • single-storey and rear extensions cannot be higher than 4m
  • multi-storey rear extensions cannot exceed the rear wall by more than 3m in length (if an attached house) or 4m (if detached)
  • materials must be similar in appearance to the existing building
  • eaves and the ridges cannot be higher than the existing house.

All alterations to listed buildings, including internal ones, require Listed Building Consent for any building operations.

Building Permits U.S.A.

If you are making significant changes to your home you need to have Building Permits, as well as proper building inspections during the process and at the project's completion.

The first thing you need to do is to submit a permit application to the local community development department that will review your permit application and project plans.

Counties, town and municipalities require homeowners to obtain building permits before undertaking a renovation for enforcing building codes. The International Building Code (IBC) addresses do's and dont's when it comes to remodelling or building. Your community may also have additional codes dealing with other important aspects such as, energy, waste reduction, quality of air, etc.

The "Permit Required" list includes the following activities:

  • demolishing a load-bearing wall
  • changing the house's roofline
  • installing new electrical wiring
  • installing a fence over a certain height, such as 6 ft (mt)
  • any type of action with the sewage system
  • exterior doors, windows and skylights that require new openings
  • installing fireplaces
  • installation of a new water heater

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Type of house extension options

The right house extension for you largely depends on the space available and the layout of your home. What really matters is that the type of home addition that you want, be appropriately matched with the building type.

The method of connection requires careful consideration, in particular, with regard to openings between the existing building and the extensions, junctions with the roof structure, the positions of drainage, etc.

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There is also a number of different house extension types, generally depending on where they are built on the house. They include:

  • garage and rear extensions
  • single, double or multi-storey
  • cellars or basements
  • outbuilding (outhouse), orangeries and conservatories
  • loft conversion like mansard and dormers
  • wrap around house extension

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Single-storey extensions

This one is the most popular and commonly chosen types of extension. It is often used to, for example, extend a kitchen. Single-storey house extensions are built onto a part of the house where one or more sides of the extension are attached to the property. Single-storey extensions require building control but they might not require planning permission.

Double-storey extensions

Double-storey extensions are built from two levels of the property. This choice largely depends on the layout of your home. In addition, the main limitation of a double-storey extension is usually the roof height since the height of its ridge and eaves should not be taller than the existing roof.

Rear and back extensions

Rear extensions are usually built out into the garden area. They’re popular for opening up the house while enhancing the flow between interior rooms and the garden. It can include internal property alterations such as to open up your kitchen to the back garden and create an open-plan area combining kitchen, living and dining area.


A basement is part of a building that is either partially or completely below ground level. Building regulations in this case will cover areas including damp proofing, ventilation, drainage, means of escape, etc.

Garage extensions

This type of extension doesn’t require to build additional external walls but simply implies refurbishment of your existing garage in order to become a more functional part of the house, unless you plan to build an over-structure extension. In fact, many UK properties (detached & semi-detached) built within the last 40 years, usually have a single storey side garage. This creates an opportunity for an additional extension on top of the garage.

Outbuilding, orangeries and conservatories/sunrooms

An organgery (also called sunroom) is similar to a conservatory but it has a solid roof and walls as well as glazing. They are fairly simple structures to build being usually made of UPVC, timber or aluminum. A sunroom is essentially a conservatory with one of the solid roof extension types and walls, including glazing. Traditionally separated from the main house all these structures remain a popular add-on, particularly to period buildings, and are ideal to bring in a lot of sunlight.

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Wrap around home extension

They are created by combining a side and a rear extension together, creating an L-shaped wrap around extension. This type of extension is very flexible and increase value to your home; however you need to consider the overall design balance and the more disruptive nature of this extension type.

House extensions: Building materials

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Material choice is crucial to the design of extensions while most house extension materials need to match the existing property for the walls and roof. This is also a Planning permission requirement and a condition for permitted development extensions. However, using contrasting materials could occasionally provide a better visual impact and make your extension stand out from the crowd.

Timber cladding is a frequent material choice which adds a more rustic aspect to the house extension structure. For a more contemporary look, you can opt for a mix of white-painted render, grey slates and lots of glazing.

Here we give an overview of the types of construction materials that may be most suitable for your project.

  • masonry construction (brick and block, stone walling, concrete)
  • timber frame construction (traditional green oak, rammed earth, post and beam, Tradical Hemcrete, )
  • steel structures
  • glazing



House extension design ideas

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You will find that Edificius by ACCA software is a smart solution to create highly detailed construction drawings providing very powerful architectural design tools already used by thousands of professionals all over the world involved in home design, remodellings, landscaping and construction cost estimating facilities together with an integrated real Time Rendering view for producing high quality archviz video presentations and simulations.

The Video below will show you the step by step procedure to model your house extensions with a BIM software.


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