Before the builders arrive: what has to be in place before work starts
· 10 min read
Before building work starts on a London house, you need a measured survey, finished drawings, any planning approval the scheme needs with its pre-start conditions met, party wall notices served, building control arranged, structural calculations and, on almost every job, a principal designer and principal contractor appointed in writing. A home built or refurbished before 2000 needs an asbestos survey, and building near a public sewer needs Thames Water's agreement.
None of it is difficult, but every item is a reason a start date can slip, and several run on legal clocks of one to two months. This is the checklist for the weeks before work begins: what each item is, why its absence stops or delays the start, and how long to allow. For the whole journey in order, from the first budget to handover, see planning a house extension step by step.
How long does each item take?
Work backwards from the day you want to start. These clocks are set by law:
- Party wall notices: two months before work to a party wall, one month before a new wall at the boundary or digging near a neighbour's foundations. A neighbour then has 14 days to reply.
- Planning permission: the council has 8 weeks to decide a householder application, from the day it validates it.
- Prior approval for a larger rear extension: work must not begin until the council confirms in writing that it approves, or that no approval is needed, or 42 days pass without a decision.
- Lawful development certificate: the council has 8 weeks from the day it receives the application.
- A planning condition to be met before work starts: up to 8 weeks for the council to decide a request to discharge it.
- Building control on full plans: a decision within 5 weeks, or 2 months if you agree to the longer period.
- Protected trees: 8 weeks for the council to decide on work to a tree under a preservation order, and 6 weeks' notice before most work on a tree in a conservation area.
Many of these can run at once. Party wall notices can go out while the planning decision is pending, and the building regulations drawings can be drawn in the same weeks. Left to the end, each clock adds its weeks to the start date.
Which surveys come first?
Measured survey: every drawing, application and price is drawn from it, so an error in the survey is copied into everything that follows, and it surfaces on site as a beam that does not fit or a floor level that does not meet. MVV's initial drawings include it.
Asbestos survey: HSE warns that asbestos may be in any home built or refurbished before 2000. The law requires the firm doing the work to find out whether asbestos is present, or to presume that it is, before work that could disturb it begins. A survey before the strip-out lets the programme allow for whatever it finds, rather than stopping the job when a ceiling comes down. Indicative London prices run from £280 to £700 per home, ex VAT. Our guide to design costs in London sets out what each survey costs.
Is there a public sewer near the work?
If an extension comes within 3 metres of a public sewer, or within 1 metre of a public lateral drain, you need Thames Water's agreement to build over or near it, and Thames Water is clear that construction should not start before the agreement is in place. Planning permission does not give that consent. Its charges, updated each 1 April, are £130, £490 or £585 by the size of the sewer, the largest plus legal costs from £1,000. Some pipes cannot be built over at all and have to be moved, which is a separate application to Thames Water.
A drainage survey by your builder or a drainage specialist shows where the sewers and drains run and how big they are, which tells you whether you need an agreement at all. A sewer changes the building control route too, as the section on building control explains.
Is the planning consent in place?
Holding a planning permission or a prior approval is not quite the end of the planning work:
- Read the conditions. A condition worded "no development shall take place until" must be met before any work starts, and the council has up to 8 weeks to decide a request to discharge it.
- Check the date. Work normally has to begin within three years of the permission being granted, unless the permission sets a different period.
- A listed house needs listed building consent for any change that affects its character, inside or out, and the council has 8 weeks to decide. Working without it is a criminal offence.
- An extension of 100 m² or more must claim the Community Infrastructure Levy exemption for your own home before work starts. Claimed late, the levy is payable in full.
Where the work is permitted development, a lawful development certificate is optional, but it confirms in writing that the work is lawful, which protects you when you sell.
Have the party wall clocks run?
Party wall notices belong on this list because the work they cover has to wait for the notice period, and where a neighbour does not agree in writing, the surveyors' award records the terms on which it goes ahead. Timing cuts both ways: a notice for work to a party wall lapses if the work has not begun within 12 months of serving it, so serve it once the scheme is settled, not at the first sketch. Our guide to party wall agreements explains the notices, the surveyors and who pays.
Is building control arranged, and the structure designed?
Building control checks the work against the Building Regulations, through the council or a registered building control approver, and there are two ways in:
- Full plans: the drawings are checked and approved against the regulations, so the builder works to approved drawings. The law requires this route where you build over a sewer or drain shown on the sewer map, or where the work could block access to one.
- Building notice: nothing is approved in advance, and work can start 2 days after the notice is given. GOV.UK describes it as only for smaller projects.
Where the council is checking the work, the Building Regulations also require notice that work is starting, at least 2 days before it does.
The structural design has to be ready before the work it covers, because building control checks every beam and foundation against the engineer's calculations: the foundations before the first trench is dug, the beam sizes before the steel is ordered. We provide structural engineering ourselves, and our full design package includes the building regulations drawings and the building control application.
Are the CDM appointments made in writing?
Health and safety has its own paperwork, and it has to exist before the first day on site. Subcontractors count as contractors, so nearly every home project has more than one, and the Construction (Design and Management) Regulations 2015 then require a principal designer and a principal contractor, both appointed in writing before construction begins. Before the site is set up:
- The principal contractor draws up a construction phase plan: the health and safety arrangements and the site rules.
- A larger job, lasting more than 30 working days with more than 20 people working at once, or more than 500 person days in all, is notified to HSE before construction begins.
At MVV, the principal designer's role is included in our design and build service.
Who else needs to know before work starts?
Some councils want to know how the site will run before it opens: deliveries, parking, noise and dust. Camden asks for a construction management plan with every basement, Wandsworth for an engineer-signed one on confined sites, Westminster applies its Code of Construction Practice at the highest level to any new or extended basement, and Kensington and Chelsea asks for a draft construction traffic management plan with a basement. Where a plan is needed, allow from £750, indicative and ex VAT. See our guide to basement conversions in London.
The street has its own permissions. A skip on a public road needs a licence, which in most areas the skip company obtains. Scaffolding or hoarding on the pavement needs a licence from the council: in Merton, for example, the scaffolder or contractor applies, and nothing may go up before the licence is issued.
Tell the neighbours what is coming and when, with a name and a number for the site. Tell your home insurer about the work before it starts and ask what it needs from you, and ask your builder for its insurance certificates.
Will the gas, electricity or water need moving?
Look at what the work touches: the gas meter, the incoming electricity and water, the boiler and its flue, the drains. If any of them has to move or be upgraded, find out early who does that work and how far ahead it has to be booked, because it is not always your builder. Decide too where you will live, cook and wash while the work goes on, and which rooms stay in use.
Are the specification and finishes decided?
A builder can only price and order what has been chosen. The kitchen, windows, rooflights, tiles, sanitaryware and joinery all need specifying before the price is final, and anything made to order has to be ordered before the trades need it. Moving a wall on a drawing costs a redraw; once it is built, it costs the rebuild. Our article on deciding early explains how late changes add cost and time, and the free tools in our Design Studio let you test the costs and the look of the rooms first: the second fix calculator, for one, lists the materials for the finishes so they can be chosen and priced before the start. For the order the work runs in once it begins, see what order to renovate a house in.
What should be signed before the first day?
The last two documents turn a set of approvals into a start date. The programme shows every stage in order, with the dates by which decisions and deliveries are needed. The payment schedule ties each payment to completed work, not to dates. Both belong in a written contract, signed before anyone starts. Our guide to choosing a building company covers the contract, the insurance checks and the questions to ask.
Where to start
Most of this list comes out of the design work: the survey, the drawings, the planning application, the building regulations drawings and the structural calculations. That is why design comes before the build, and why it matters who is on your side from the start. MVV's own fees for a single-storey extension under 100 m², indicative and ex VAT: initial drawings, covering the measured survey, design options, the planning drawings and making the application, £800 to £1,120; the full design package, which adds the building regulations drawings and the building control application, £2,000 to £3,000. If you are weighing one firm for everything against a designer and then a builder, see design and build or the traditional route.
- See which surveys, approvals and fees your home is likely to need with the free design cost calculator.
- Plan the project online before you call anyone, with our free design tools.
- Book a free consultation when you are ready to start the clocks.
Good to know
Frequently asked questions
- What needs to be done before building work starts on a house in London?
- Three kinds of thing. Information: a measured survey, finished drawings, structural calculations and, for a home built or refurbished before 2000, an asbestos survey. Permissions: any planning approval with its pre-start conditions met, building control, party wall notices, and Thames Water's agreement near a public sewer. The site: a principal designer and principal contractor appointed in writing, a construction phase plan, licences for skips and scaffolding, and a signed contract with a programme and payment schedule.
- How long does it take to get everything ready before building work starts?
- It depends on which clocks apply to your home, and they can run at the same time. Among the longest: two months' notice for work to a party wall, 8 weeks for the council to decide a householder planning application once validated, and up to 8 weeks more to discharge a condition that must be met before work starts. A full plans decision takes up to 5 weeks. Started late, the same clocks run one after another.
- Can I start building with a building notice instead of full plans?
- For a smaller, simple job, yes: work can start 2 days after a building notice is given, though nothing is approved in advance. Full plans means the drawings are checked first, with a decision within 5 weeks, or 2 months with your agreement. Building over a sewer or drain shown on the sewer map, or work that could block access to one, requires full plans by law.
- Do I need an asbestos survey before renovating my house?
- If the house was built or refurbished before 2000, it is the sensible start. HSE warns that asbestos may be present in any such building, and the law requires the firm doing the work to find out, or to presume it is there, before disturbing it. Indicative London prices run from £280 to £700 per home, ex VAT, a small cost beside a stopped job.
- Do I need a build-over agreement for my extension?
- You need Thames Water's agreement if the extension comes within 3 metres of a public sewer or within 1 metre of a public lateral drain, and construction should not start until you have it. A drainage survey shows where the pipes run. Thames Water charges £130, £490 or £585 by the size of the sewer, the largest plus legal costs from £1,000.
- What has to be in place for health and safety before work starts?
- Two written appointments and a plan. Where more than one contractor will work on the job, which subcontractors make almost certain, a principal designer and a principal contractor must be appointed in writing, and the principal contractor must prepare a construction phase plan before the site is set up. Only a larger job also has to be notified to HSE: one lasting more than 30 working days with more than 20 people working at once, or more than 500 person days in all.
- Do I need to tell my home insurer before building work starts?
- Yes. Building work can change what your home insurance covers, so tell your insurer before work starts, and again if the house will be empty while it goes on. Ask the builder for proof of their own insurance too, public liability and cover for the works, and check who insures the work until it is handed over.
