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Adding an extension to your house has always been a good way to gain space, but with increases in stamp duty, mortgage rates and property prices extending your home is a very popular option. The benefits include increasing your house value, adapting the space to meet your needs, making the most of existing underused areas, improving energy efficiency and avoiding the costs and hassle of moving.

House Extensions

House Extension Planning

An extension can take many forms and have varying build costs so it very important to spend time at the planning stage to avoid costly mistakes. The priority is to identify the extension’s purpose and how it will fit in with the rest of the house. The current internal layout needs to be considered, making changes to this along with extending not being overlooked.

A maximum budget needs to be identified and the new extension designed to be achievable within this. There is no point in going beyond your means it only results in disappointment at the construction stage and the possibility of not getting a return on your investment.

A badly designed extension will not improve your house, it can make existing spaces less appealing and waste your money.

Use a Professional

If you are considering a house extension it is important to employ professionals who have the knowledge to create the new spaces safely whilst complying with the Building Regulations, Planning Legislation, the Party Wall Act, Health & Safety and when required Listed Building Consent.

Architecture First have over 30 years of experience designing house extensions for all types of properties creating new spaces for you to enjoy and raising the value of your home. We will design your house extension in 3D making it easier for you to visualise the new spaces. When required Planning Permission will be gained and for all house extensions Building Regulation Approval and for listed buildings Listed Building Consent. A full set of architectural drawings, specifications, and structural details will be supplied for all home extensions. Details of our home extension fee packages can be found here.

To obtain a price for our services please complete the enquiry form or contact us and we will get back to you with our fee.

Extension Material Selection

Using the correct materials is crucial. If you are using permitted development rights, they must match those which have been used to build the existing house. If planning permission is to be gained then there is more flexibility but, in many cases, planners will want matching materials or those which are sympathetic to the existing, especially when the extension can be viewed from the public realm in a conservation area.

If matching materials are available, then a viable option is a traditional extension which will blend in with the existing and once the materials have weathered the new addition will become seamless with the original.

The other option is a contemporary extension which will be a complete contrast to the existing property allowing both styles to shine and compliment each other. This doesn’t always mean that a radical design is used with a more subtle approach being adopting a different form and alternative materials.

Where possible we look at using sustainable materials.

A home extension is going be a long-term investment and its longevity needs to be considered at the design stage to avoid further remodelling in the future. Remember what is in fashion today may not be tomorrow so think about date stamping the extension with current trends that could be costly to reverse in the future. If the house isn’t a forever home personal tastes could limit the number of potential buyers when the property is put on the market.

Permitted Development

In recent years Permitted Development has made extending your house easier, however there are conditions and limitations that must be met. For many extensions complying with these won’t restrict the design but the option of gaining planning permission will allow more scope so this shouldn’t be ignored.  In all cases Building Regulation Approval will be required to ensure, for example:

  • the new walls, ceilings, windows, roofs, and doors are thermally efficient

  • the stability of the existing structure is not compromised

  • the structural strength of new floors, walls and roofs is sufficient

  • there is safe escape from fire

  • new and existing spaces are correctly ventilated

  • stairs are safely installed and to use

  • electrics, plumbing, and heating are completed by competent installers

  • reasonable sound insulation between rooms and adjoined properties.

  • new above and below drainage is the correct size with adequate flows

Permitted Development Extensions

  • Rear Single Storey Extensions

  • Double Storey Rear Extensions

  • Side Single Storey Extensions

  • Side Double Storey Extensions

  • Side Return Extensions

  • Front Extension (Porch)


Building Regulations


All extensions will require building regulation approval and we recommend that a full plans application is always used to ensure that all aspects of the regulations are correct before the construction phase begins. This type of application is completed in two stages, firstly the plans and information are checked for compliance and followed by site inspections once the building work is underway. Sometimes structural elements of the extension and alterations will need structural calculations and details to be provided by a structural engineer. There may be requirement to notify a neighbour in accordance with the Party Wall Act etc. 1996 and if you intend to build over or within 3m of a public sewer a Build Over Agreement needs to be in place before the construction work begins. If your property is in a Conservation Area, it’s likely that the materials will have to match the historic palette and the design will have to fit in with the context or be sympathetic. Extensions to a listed building will have to meet this requirement too and listed building consent will be required.

Home Extension Types

Front Extensions

Single and double house extensions can be added to the front of properties but predominantly they are single storey with the most popular being a porch which can be designed to comply with permitted development rights. Other single storey extensions can be added with planning permission, and these allow for the depth of existing rooms to be increased. A bay window to a living room with a canopy the width of the house is common. Some properties allow for a small double storey extension, and these can enable existing bedrooms to be enlarged or an ensuite to be added. Permission for a larger double storey front extension is more difficult to obtain unless the property is set back substantially from a highway.  

Single Storey Side Extensions

Single storey house extensions offer the opportunity to add additional rooms to the ground floor of your home including, bedrooms, bathrooms, a utility room, home office, an ensuite, sitting room etc. They can also enable existing rooms to be enlarged when walls are knocked through. The size of the extension will be dependent on the land which is available at the side of your property and whether access is still required to garden areas. This type of extension can be added to semi-detached and detached houses, bungalows, and some end terraced houses. Detached properties can have land at both sides which can allow for more than one single storey side extension to be added. A single storey side extension can be designed to meet the requirements for permitted development or if this restricts the design options planning permission can be gained.

Double Storey Side Extensions

Double storey house extensions are a cost-effective way to add new rooms to the ground and first floor of your home with construction costs per m2 being less than a single storey extension. They enable the creation of new rooms or the existing to be enlarged with knocking through and this also introduces the opportunity to remodel existing layouts. A double storey side extension is a popular way to add an ensuite bedroom with the configuration of traditional houses allowing for the new access from existing landings and hallways. This type of extension can be added to a semi-detached and detached house, bungalows, and some end terraced houses. Detached properties can have land at both sides which can allow for more than one double storey side extension to be added. A double storey side extension can be designed to meet the requirements for permitted development but there are more restrictions so often planning permission is required. When building higher further consideration needs to be given to overlooking, the right to light and overshadowing. Many councils request that the extension is subservient to the existing with new walls being stepped in from the existing and new roof heights being lower to protect the appearance of the street scene and prevent the terracing effect.


Single Storey Rear Extensions

A single storey rear house extension is a popular way to increase the living space of your home whilst also adding value to your property. Typically, a section of wall is removed to link the extension to the existing living area to create an open plan living space incorporating a kitchen, dining, and seating area with large patio or bifold doors leading to outside spaces.  Or the space is subdivided to allow new rooms to be formed such as an enlarged kitchen, home office, bedroom, and bathroom. This type of extension can be added to  semi-detached and detached houses, bungalows, and terraced houses. A single storey rear extension can be designed to meet the requirements for permitted development or if this restricts the design options planning permission can be gained.

Double Storey Rear Extensions

A double storey rear extension is often a budget-efficient way to gain extra living space and avoid the need for moving home. Adding another storey is less expensive because the foundation and roof cost are already included in a single storey extension. The ground floor of a double storey extension usually provides a new space along the lines of a single storey extension whilst the first floor allows for remodelling of the existing floor plan and the creation of new rooms. A double storey rear extension can be added to a terraced, semi-detached, and detached house when there is sufficient outside space. This type of extension can be designed to meet the requirements of permitted development rights; however, these are more restrictive than single storey so planning permission is often required.

Side Return Extensions

A side return house extension is a great way to make use of the underused outside space of a semi-detached or terraced house. A side return is the narrow strip of land that runs alongside the house at ground level. Sometimes this can be 1m or less but even extending into this space and knocking through can make a difference to a galley kitchen proving space for a table or additional units. When the space is larger it’s possible to create a dining or seating area. A further benefit is the opportunity to introduce light from above making existing spaces brighter. A side return extension can be designed to meet the requirements for permitted development or if this restricts the design options planning approval can be gained.

First Floor Extension

Many properties have already been extended to the ground floor or had single storey sections when originally constructed including garages and outhouses. Adding a storey above these is possible and cost effective but it will depend upon the structural stability of the existing building. Even when this won’t carry the additional weight the extension is still possible with the introduction of new structural elements or improving the load bearing capabilities of the existing. Benefits of building above an existing structure is it won’t impact on your garden space and the new room is often easily linked to the existing first floor. This type of extension usually requires planning permission.

Orangery Extensions

The popularity of orangery extensions is on the rise with homeowners opting to build these opposed to conservatories because they are more practical for all year-round use. First introduced in the UK in the 18th century they are generally constructed with low walls, glazing above and French doors. A flat or a low-pitched hipped roof that incorporates roof lanterns is common. Perhaps better suited to period properties the design can also be adapted to suit contemporary applications. An orangery provides a multi-functional extension with common uses including a kitchen, dining room, living room, study, garden room and often link the inside to the garden. The orangery interior is light and airy making existing rooms brighter when knocked through. Along with the additional space there are benefits of improved thermal gains and lovely views of outside. An orangery extension can be designed to meet the requirements for permitted development or if this restricts the design options planning approval can be gained. They can be added to a terraced, semi-detached, and detached house and a bungalow when there is sufficient outside space.

Combination Extensions

A house extension need not to restricted to one type and often a combination of extension types with a mix of floor levels will be used, for example, a rear extension that is deeper than the storey above. 


Using Architecture First from the outset will allow for an extension design that meets your requirements and can be built within your budget with all permissions and approvals being in place.

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