Resmor's guide to home extensions and loft conversions in Surrey

When a house needs more room, most owners weigh the same two options: build out at the back or side, or build up into the roof. This guide sets out what each involves in Surrey and South London, which approvals you need and how the work runs.

It is a summary of the national rules for England as we understand them at the time of writing. They change, and local limits apply, so confirm the detail with your council before you rely on it.

Extension or loft conversion?

A home extension adds floor area at ground level, most often for a larger kitchen and family room. It uses some of the garden and it needs foundations, so ground conditions and drains affect the cost.

A loft conversion adds a bedroom, often with a bathroom, without touching the garden. Whether it is possible depends on the roof. As a rule of thumb you need about 2.2 metres from the top of the ceiling joists to the underside of the ridge, and room for a staircase on the floor below.

Many houses can take both, and doing them as one project means one period of disruption. Either way it helps when one team carries the job from the first visit to the last snag, which is how we run our home improvements work.

Do you need planning permission?

Not always. Many houses have permitted development rights, which allow some extensions and loft conversions without a planning application.

Extensions under permitted development

The main limits for a house in England are:

• A single-storey rear extension may reach 3 metres beyond the original rear wall on a semi-detached or terraced house, and 4 metres on a detached house
• Under a separate prior approval process, in which the council consults your neighbours, those figures can rise to 6 and 8 metres
• A single-storey extension may be no more than 4 metres high, and no more than 3 metres high at the eaves if it is within 2 metres of a boundary
• A two-storey rear extension may reach no more than 3 metres beyond the original rear wall and must stay at least 7 metres from the rear boundary
• A side extension must be single storey and no more than half the width of the original house
• Extensions and outbuildings together must not cover more than half the land around the original house
• Nothing may be built forward of the front of the house, or of a side that faces a road
• The outside materials must look similar to the existing house

Loft conversions under permitted development

• The added roof space must not exceed 40 cubic metres on a terraced house, or 50 cubic metres on a detached or semi-detached house, counting any earlier roof additions
• No dormer or extension on the roof slope that faces the road
• Nothing higher than the highest part of the existing roof
• Dormers set back at least 20 centimetres from the eaves where that is practicable
• Side windows obscure-glazed, with any opening part at least 1.7 metres above the floor
• No balconies or raised platforms
• Materials that look similar to the existing house

When these rights do not apply

• Flats and maisonettes have no permitted development rights of this kind
• Listed buildings need listed building consent for almost any alteration
• In conservation areas, and in National Landscapes such as the Surrey Hills, roof extensions, side extensions and two-storey rear extensions need a planning application
• Some houses, often on newer estates, have had the rights removed by a planning condition

Much of Surrey is also Green Belt. Permitted development still applies to most houses there, but a larger scheme that needs a planning application will be judged on how much it adds to the original building.

If you are unsure, ask the council, or apply for a lawful development certificate, which confirms in writing that the work does not need permission. It is optional, and useful when you come to sell.

Building Regulations: needed almost every time

Planning is about whether you may build. Building Regulations are about how it is built. Nearly every extension and loft conversion needs approval.

Building control checks, among other things:

• The structure: foundations, beams, floor joists and the roof
• Fire safety. In a loft conversion this usually means a protected route down the stairs, fire doors and linked smoke alarms
• Insulation and ventilation
• Stairs, including headroom
• Drainage
• Electrical work

You can use the council’s building control service or a registered building control approver. Either inspects the work at set stages and issues a completion certificate at the end. Keep that certificate. A buyer’s solicitor will ask for it.

Party walls and neighbours

If you share a wall with a neighbour, or plan to dig near their house, the Party Wall etc. Act 1996 is likely to apply. Typical cases are steel beams for a loft conversion that rest in a shared wall, and foundations for an extension dug within 3 metres of the neighbouring building and deeper than its own.

The Act asks you, as owner, to give written notice: normally at least two months before work to a shared wall, and one month before excavation near a neighbour or a new wall at the boundary. The neighbour can agree in writing, or a surveyor is appointed to settle the terms. This is separate from planning and from Building Regulations, and it is worth starting early.

What decides the cost

We do not publish prices, because two jobs of the same size can differ widely. The things that move the figure are:

• Size and shape, and how much structural steel is needed
• Ground conditions, and drains or manholes in the way
• The type of loft conversion: rooflights only, a rear dormer, or a hip-to-gable change to the roof
• Glazing, especially large sliding or folding doors
• The kitchen or bathroom going in, and the standard of finish
• Access for materials and waste
• Professional and approval fees
• VAT

A written, itemised quotation shows which of these you are paying for, and makes it possible to compare one builder’s price with another’s.

How the work runs

1. First visit. We look at the house with you and talk through what you want.
2. Design and approvals. An architect or designer draws the scheme, and a structural engineer sizes the beams and foundations. Planning, building control and party wall matters start here.
3. Quotation. Written and itemised, from the agreed drawings.
4. Build. One site manager on your job, and a weekly update in writing.
5. Inspections. Building control visits at the set stages.
6. Handover. The snag list is closed first.
7. Aftercare. A written warranty on our work, and product claims handled for you.

Approvals often take longer than people expect. Councils aim to decide a householder planning application in about eight weeks, and party wall notices add their own notice periods, so allow for both before you fix a start date.

Where to start

Send us a few photographs and we will tell you what is possible. You can start an enquiry and we will call you back to arrange a visit.

If you are still comparing firms, read how to choose a builder in Surrey. Once the work is finished, our guide to property maintenance in Surrey covers how to look after it.