The first rule when extending a period property is: don’t try to turn a cottage into a castle. Extensions that are out of scale and context mean that you risk losing the character and history which initially attracted you to the building, plus they’re likely to make the internal proportions of the property feel unbalanced.

Many old properties don’t suit modern lifestyles, so changes are inevitable and part of a building’s natural evolution. Extending successfully relies on understanding how the internal spaces work, a respect for the age and history of the property, achieving appropriate scale internally and externally, as well as a careful choice of materials.

Design considerations

Plan the extension so that it doesn’t detract from the proportions or key features of the existing building and try to maintain the ‘rhythm’ of the architecture. Above all, do ensure that it enhances rather than detracts from the look of the property. Think about this particularly carefully if it’s part of a terrace – anything you do to the front or the back of the house could spoil the appearance of the entire row.

This does not mean it has to replicate the original architectural style or materials. It’s worth remembering that many period properties are beautiful because of later additions from different eras. Rather than poor pastiche, good modern design – which is honest to the style of architecture today – frequently works better and creates exciting living spaces.

Conservatory

Think carefully before adding a conservatory. These were a Victorian invention and were used as an addition to larger houses, so they can look wrong on buildings of earlier eras and were never found on smaller homes. While there are some good modern reproductions, remember that simple is often best – originally the frames were cast-iron or timber and this is reflected in the fine quality of the detailing. In comparison, uPVC versions can be cumbersome.

Reversibility

Reversibility is another issue to think about. Try to design an extension so that it can be removed in the future with minimum damage to the historic fabric of the building. For example, make it an independent structure with the minimum number of fixings to the old building. The same considerations apply when deciding how to access the new space from the old. If possible, avoid knocking holes in original walls and instead use and incorporate existing window or door openings.

Materials

Bear in mind that traditional materials behave differently to contemporary products, such as cement – when used inappropriately, they can cause damp and other issues. In addition, due to differential settlement, problems can occur when a new extension with deep foundations is attached to an old building with shallow foundations, so ensure that the junction between the two allows for movement.

Modern building regulations may prevent a copy of the construction methods used in the original structure. Even so, it is still possible to use lime mortars, plasters and renders and materials like hemp lime or clay blocks for building, which have the added benefit of being eco-friendly.

Rules and regulations

As well as planning permission and building regulations, a key consideration is whether your property is listed or lies within a conservation area. If you plan to alter or extend a listed building in any way that affects its character, inside or out, you must apply for listed building consent.

A good starting point for information is the government’s Planning Portal (planningportal.gov.uk). It’s also worth speaking to the conservation officer at your local authority planning department and being honest with them about the extension you’re contemplating, as the rules on extending in a conservation area will vary from area to area. They can offer good advice and may point you in the direction of the right tradespeople and professionals who can help with the build.

Getting advice

Before undertaking any work, it’s worth doing some research to understand the building’s history and the materials and techniques used in its construction. The Society for the Protection of Ancient Buildings (020 7377 1644, spab.org.uk) offers publications, runs courses and has a free advice line, while The Georgian Group (087 1750 2936; georgiangroup.org.uk) and The Victorian Society (020 8994 1019, victoriansociety.org.uk) have useful guides.

Extending a period property: Case studies

A sympathetic two-storey extension to a Georgian home

The existing extensions to the side and rear of this Grade II-listed Georgian property, which stands within a conservation area in Littlehampton, West Sussex, were in a state of collapse. The only option was to demolish and rebuild them.

Georgian house with crumbling extensions

The owner drew up plans for the new two-storey extension before contacting an architectural technologist to produce drawings in order to apply for planning and listed building consent. An eight-month battle with the local authority ensued, as it was concerned that the new extensions would create a pastiche.

Georgian house with sympathetic two-storey extension

Permission was eventually granted, and care was taken to ensure the extensions appeared original, with the walls rendered to the front elevation and faced with flints to the rear. A pitched roof replaced the flat roof and new windows to the front of the extension were copied to match the timber sashes in the older part of the house. Central heating was extended into the new space. The two-year project cost £100,000.

Creating a contemporary space in a Victorian house

This Victorian property, which is in a conservation area in Hackney, north London, had a contemporary side extension added to it to create an open-plan kitchen-diner that connects the house to the back garden.

Modern glass extensions to Victorian home

The expansive glass roof opens up the view to the sky, allowing natural light into previously dark areas. Meanwhile, the modern oriel window that’s part of the new extension juxtaposes with the original Victorian bay at the front of the house that projects into the street.

Modern oriel window in Victorian house extension

Importantly, the alterations to the existing house provide a modern contrast with the existing rough walls of London stock brick that form part of the design in the dining area.

Modern glass extension with dining room in Victorian house extension

The extension cost around £80,000 to build, while the refurbishment of the entire house, including the extension, took around 10 months.

Contact: Architect Platform 5 Architects; 020 7739 9812, platform5architects.com.

Roger Hunt is co-author of The Old House Handbook.

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