Guide to extending an old house

Expert advice from Roger Hunt on how to extend a period home with practical considerations for external aesthetics and space functionality

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Extensions add space and interest to a home and, over time, these accretions form part of the building’s history. Even so, it is wise to try to buy a property that suits your needs rather than extending it in an attempt to turn a cottage into a castle and, in the process, destroy the character and features that attracted you to it in the first place.

Always ask whether you really need to extend and consider whether it might be better, cheaper and less disruptive to move to a larger home.

If you do decide that an extension is the answer, the most obvious solution is usually to build out to the back or side of the house, but it is worth considering whether it may be better to extend into the loft space or, if you are lucky enough to have one, the cellar or basement. The downside of these latter solutions is that the work involved can cause significant damage to the building’s existing fabric, structure and layout.

Tom Howley contemporary extension to Gothic stone house

Contemporary extension with full-height glazed sliding doors to stone Gothic country home, with bespoke Shaker-style kitchen by Tom Howley, where complete kitchens start from £35,000

Alternatives to extending

An often overlooked means of gaining extra space is to construct an outbuilding in the garden. With an older building this may be the most cost-effective and least disruptive solution. Many companies specialise in these garden rooms and they can serve as an office or studio, or provide overflow accommodation, complete with kitchen and bathroom.

Another advantage is that some purpose-built cabins are designed to enable you to take them with you if you decide to move, so the money you have invested is not lost.

Westbury garden room extension to Victorian home

A timber frame extension with vaulted ceiling to this beautiful Victorian house has created a spacious kitchen-diner. Expect to pay around £60,000 for a similar design from Westbury Garden Rooms

Extending sympathetically

A carefully sited and designed extension will maintain the architectural “rhythm” and symmetry of the building it is associated with and be subservient to it, thus avoiding compromising the overall shape, scale and proportions of the main house. Creating a visual break between the original building and the new addition can help achieve this, perhaps with a small link-way that acts as a corridor.

Where your home is part of a terrace, consider the whole row of houses and try to avoid alterations that will spoil the overall appearance of the street. This does not necessarily mean that you cannot be bold and embrace contemporary styles. When done well, a modern design works much better alongside an old building than a poor pastiche, but do try to use a harmonious materials palette.

Remember that past generations rarely tried to replicate what had gone before and instead followed the fashions of the day. This approach should be considered, and is also more likely to create internal spaces that suit modern lifestyles.

Top tip

Some local authorities produce design guides on extension types that might be acceptable — ask the conservation officer for details

At the same time try to minimise the damage done to the original building whilst extending. For example, making an existing window opening into a door will cause less damage than knocking through a completely new opening. Try to preserve features such as architraves, skirtings and cornices in the older part of the building, which are easily lost.

The way in which a new space will be used is often overlooked when planning an extension. The room an extension is built off can easily become little more than a corridor, with the result that a comparatively small amount of extra space is actually gained.

Think about how you and your family will circulate through both the existing and new spaces, and plan how these will be used and how furniture will be located so that the spaces flow. Where possible provide a link with the outside so the extension flows into the garden, creating a greater feeling of space.

Chris Dyson side return kitchen-diner with rooflight and Crittal doors

Extending into the side return of this Victorian terrace has allowed for a flexible kitchen-diner. A frameless rooflight and Crittal steel-framed French doors maximise light and complement the house’s period style. Expect to pay around £80,000 for a similar design at Chris Dyson

Practical considerations

A new extension can rarely be constructed in exactly the same way as the original building due to the demands of modern building regulations. The foundations of a new structure are likely to be deeper than the relatively shallow “footings” generally found in older buildings, so care needs to be taken to ensure that any differential settlement can be accommodated at the junction between the two structures.

In addition, bear in mind that the original structure needs to breathe, otherwise, damp and other problems may develop. Where an old house has suspended timber floors, ensure the underfloor ventilation is not blocked.

The addition of an extension can easily result in original rooms receiving less daylight and ventilation, devaluing the “feel” of the space. Rooflights or sun tubes can help overcome this problem and staircases and light wells are good ways of introducing natural light.

Vale Garden houses conservatory extension with Lewis Alderson kitchen

A conservatory extension to this townhouse has added a bright dining area. The Edwardian-inspired kitchen by Lewis Alderson, from £35,000, is fitted with a mirrored splashback to reflect light around the space

Planning permission

If your home is in a Conservation Area, in area of special interest, or listed you have to gain consent before extending. If not, you may be surprised what you can do under what is known as your permitted development rights. Permitted development allows you to make certain alterations (such as a smaller extension) without seeking planning permission.

Under the rules, the ‘original’ (as it stood in or prior to 1948) rear wall of a detached home can be extended (subject to the neighbour consultation scheme) within theses constraints:

  • You can extend by up to 8m in depth with a single-storey extension on a detached home
  • You can extend by up to 6m with a single-storey extension if you live in a semi or terrace
  • Single-storey extensions must be no higher than 4m
  • If your proposed new extension will be within 2m of a boundary, then the eaves height is limited to 3m
  • Two-storey extensions can be no higher than the house
  • Two-storey extensions can project up to 3m from the original wall, so long as it is at least 7m from the rear boundary
  • No extension can project beyond the front of the house (or an elevation that affronts the highway)
  • Side extensions can not make up more than half the width of your house
  • With the exception of conservatories, new extensions must be built of materials ‘similar in appearance’ and with the same roof pitch as the main house.

Do remember however that if the home has previously been extended, this will have used up some of your homes allocation under permitted development.


Hire the right people: Do employ architects and surveyors who are used to working with old buildings of a similar type and age to your home, but who also appreciate and understand good new design.

Be sympathetic: Do remember that a sensitively designed extension is more likely to increase the value of your home than one that is unsympathetic to the original style.

Rethink that conservatory: Do bear in mind that conservatories date from Victorian times and were associated with larger houses. This means they are not always an aesthetically good way of creating extra space.


Forget about consent: Don’t overlook the possible need for planning permission and, if you live in a listed building, Conservation Area or other area of special interest, the appropriate consent before extending. You will almost certainly have to comply with the building regulations.

Ignore maintenance: Don’t overlook future maintenance and how the older building’s gutters and windows will be accessed once an extension is built.

Use the wrong materials: Don’t forget that, if the extension is to be built of brick, old bricks are imperial sizes and new are generally metric, although traditional sizes can be sourced.