How far ahead should I start planning an extension?

If you would like builders on site in spring or early summer, the best time to start planning your extension is the autumn or winter before. Surveys, drawings, council approvals and notices to neighbours all take time, and together they can easily add up to four months or more before anyone can dig.

This post covers what has to happen before work starts, how long each step usually takes, and the useful checks you can make yourself over the winter. You can do a lot from the kitchen table, but leave anything structural, such as opening up a wall or digging down to look at foundations, to the people surveying the job.

Why winter is a good time to plan

Spring and summer are the most popular times to start building, because longer, drier days suit the groundwork and the shell of the extension. Building in winter is possible, but heavy rain slows digging, and concrete and mortar should not be laid in freezing weather, as frost can damage them before they set.

So a sensible pattern is to plan and get your approvals over the winter, then start on site as the weather improves. If the paperwork is done by then, the build is not held up waiting for a council decision.

The steps before building can start

Most extensions go through some or all of these:

• A survey and brief. The house is measured and you talk through what you want the new space to do.

• Drawings. Planning drawings if they are needed, then more detailed drawings for Building Regulations, with a structural engineer's calculations for beams and foundations.

• Planning permission or a Lawful Development Certificate. A Lawful Development Certificate is the council's written confirmation that your project counts as permitted development, which is building work you are allowed to do without a planning application.

• Building Regulations approval. This covers the structure, insulation, fire safety, drainage and ventilation, and every extension needs it.

• Party wall notices, if the work is on or near a wall or boundary you share with a neighbour.

• A build-over agreement with your water company, if you are building over or close to a public sewer.

How long each step usually takes

Councils aim to decide most householder planning applications within eight weeks of accepting the application as complete. A Lawful Development Certificate usually takes a similar time.

For Building Regulations, a "full plans" application means detailed drawings are checked before work starts. The council or approved inspector should give a decision within five weeks, or two months if you agree to more time.

Under the Party Wall Act, you must give your neighbour at least two months' notice before work on a shared wall, and at least one month's notice before digging foundations close to their house. They then have 14 days to reply.

Some of these can run side by side, but planning usually comes first, because the design can change before it is approved. Add a few weeks for the survey and drawings, and a late start on the paperwork can push the build back by months.

Does your extension need planning permission?

Many single-storey rear extensions fall under permitted development. Side extensions, two-storey extensions and larger rear extensions often need planning permission.

The rules are tighter in conservation areas. There, for example, side extensions are not permitted development, so they always need an application. Lingfield has a conservation area around the High Street, Gun Pond and Church Town, so if you live in an older part of a village or town, check the council's map before you assume anything. A listed building needs listed building consent for most changes too.

Checks you can make yourself this winter

These are all safe to do and will make the survey more useful:

• Check whether your home is in a conservation area or is listed, using your council's website.

• Read your deeds for restrictive covenants, which are rules in the deeds that can limit what you build. You can download your title from HM Land Registry if you don't have a copy.

• Note where the manhole covers are in your garden. Look, but don't lift them, as they are heavy and the chamber below can be deep. A public sewer within about three metres of the extension usually needs your water company's permission.

• Note any large trees near where you want to build, including your neighbours'. Roots and clay soil can mean deeper foundations, and some trees are protected by a tree preservation order.

• Talk to your neighbours early, especially if you share a wall or boundary. A friendly chat before any notice arrives makes the party wall stage much smoother.

• Think about how you will use the room, such as where the sink, sockets and radiators should go. Our post on how structural and building-services trades are coordinated in an extension explains why these choices matter early.

What to leave to the survey

Please don't knock holes in walls, lift floors near wiring or pipes, or dig beside the house to see how deep the foundations go. Whether a wall is load-bearing (holding up the floors or roof above it), what the ground is like and what size of beam is needed are questions for a structural engineer and an experienced builder.

These answers shape the design and the price, so they belong in the survey and drawings rather than being found out halfway through the build. Our structural and foundation work page explains how we work to an engineer's design.

How we help at the planning stage

At PCP Group, the first visit is about getting to know you and how you use your home, so we really understand what you are after before anything is drawn. We record the existing house, look closely at the structure, drainage and any party wall issues, and write a clear scope for the design and your budget.

We can work with your architect or submit planning drawings for you, make the Building Regulations submission, and then plan the build in phases so materials and trades are ready when they are needed. We are members of the Federation of Master Builders.

If you would like your extension underway next spring, now is a good time to arrange a site visit. You can find out more about how we design and build house extensions, and book a visit with PCP Group from there.