How to plan a single-storey rear extension for your home

Adding a single-storey rear extension is one of the most effective ways to gain space in an Edinburgh or Lothians home without moving. Whether you are in a Victorian villa in Morningside, a semi in Musselburgh, a bungalow in East Lothian or a terraced house in Leith, the principles are similar. Start with the practical checks before you fall in love with a glazing brochure.

Check boundaries, drains and site constraints first

Before any design work, confirm what you own and what you must protect. Your title deeds may show feus, servitudes or rights of access across the rear garden. Shared gables, boundary walls and drainage runs are common in older Scottish properties. In tenements and colonies, the back court or shared passage can limit where an extension can sit.

Commission a measured survey and a topographical survey. These show levels, manholes, services and the exact position of your house. Check for:

• Drainage runs and whether surface water goes to a combined sewer or a soakaway.
• Water, gas, electricity and broadband cables entering the property.
• Trees with Tree Preservation Orders or root protection areas that restrict excavation.
• Coal mining legacy in parts of Midlothian, West Lothian and East Lothian.
• Flood risk, especially near the Water of Leith, Almond or Esk.

A difference of half a metre can decide whether a layout works. Get this right early and you will save money later.

Understand planning permission and building warrants

Some single-storey rear extensions fall under permitted development, but that is not guaranteed. In Scotland, permitted development for a house usually allows a rear extension up to 4 metres for a detached house and 3 metres for a semi-detached or terraced house, with limits on height and materials. However, Edinburgh has many conservation areas, the World Heritage Site, listed buildings and Article 4 directions where these rights are removed.

Check with your local planning authority — City of Edinburgh, East Lothian, Midlothian or West Lothian — before you assume anything. Even if planning permission is not needed, you will almost certainly need a building warrant. Planning and building standards are separate processes.

Allow roughly 8 to 12 weeks for a householder planning application and 6 to 8 weeks for a building warrant. Applications typically need existing and proposed drawings, a location plan, a block plan, elevations, sections and sometimes a heritage statement. For listed buildings, listed building consent is also required. In Scotland, party wall matters are dealt with under common law and, in tenements, the Tenement Management Scheme. If you are excavating near a neighbour or altering a shared wall, take surveyor advice and get any agreement in writing.

Set a realistic budget before you get quotes

In Edinburgh and the Lothians, a straightforward single-storey extension often costs between £1,800 and £2,800 per square metre. A 20 square metre extension can therefore land between £36,000 and £56,000 before kitchen, flooring and decoration. High-end glazing, structural steel, underfloor heating, complex groundworks or a listed building can push costs above £3,000 per square metre.

Build in professional fees: architect or designer fees are often 8 to 12 per cent of build cost, a structural engineer may be £800 to £2,000, and the building warrant fee is based on the estimated cost of work. Add a contingency of 10 to 15 per cent. Do not forget scaffolding, skips, parking suspensions, temporary kitchen costs and VAT.

When quotes arrive, insist on an itemised breakdown. Compare like for like. A cheap quote that excludes drainage, decoration or building control fees is not cheap. Agree a payment schedule linked to completed stages, not large upfront deposits. A retention of 5 per cent for three to six months is normal and gives you leverage if snagging appears.

Choose the right build route and appoint a builder

You can use a main contractor, a design-and-build firm, or manage separate trades yourself. For most homeowners, a main contractor with a clear scope and a written contract is the least stressful route. Get at least three quotes from builders with local experience of Scottish building standards and your local authority's building control team.

Ask for references and visit completed extensions. Check public liability and employers' liability insurance, a health and safety policy, and a waste carrier licence. Agree working hours, site access, skip location and welfare arrangements. The contract should include drawings, specification, schedule of works, payment terms, variations, completion date, retention and defects period. Verbal agreements are not enough.

• Do not start on site without a building warrant and any necessary planning approval.
• Confirm who is responsible for building control notices and inspections.
• Keep a paper trail of every change, cost and instruction.

Design for light, warmth and low maintenance

Glazing choices matter. Sliding or bifold doors and roof lanterns can transform a rear extension, but south and west-facing glass can overheat in summer. Building standards in Scotland require good insulation, controlled ventilation and minimal thermal bridging. A flat roof needs a warm deck construction, correct falls and a high-performance membrane. A pitched roof should match the existing house in tiles or slate.

Think about floor levels, step-free access and underfloor heating. Plan drainage for gutters, downpipes and any new soakaway. Get a structural engineer to specify steel beams, padstones and lintels. Most importantly, design the room for how you will live: kitchen-diner, utility, WC and storage all need sensible positions. A beautifully glazed extension with nowhere for coats and boots will soon feel cramped.

Plan the build sequence and protect your home

A typical sequence runs from survey and design, through planning and warrant, to tender and appointment. On site, work usually moves through strip-out, foundations, drainage, slab, walls, roof, glazing and weathertight stage. Only then should the existing rear wall be opened up. First fix, plaster, second fix, kitchen and decoration follow. Building control will inspect at key stages, and you should receive a completion certificate at the end.

Protect your home during the work. Expect dust, noise and lost access to the garden. Set up a temporary kitchen if needed, cover floors and radiators, and keep neighbours informed with a short letter and a contact number. In Edinburgh, parking suspensions and skip permits need to be arranged in advance. Agree a snagging list before final payment, and keep your retention until you are satisfied. A well-planned rear extension is a major project, but with boundaries, permissions and budget sorted first, it can be a genuinely enjoyable one.