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Extensions · Specialist guide

Extension Groundworks Checklist

Reviewed byA Jones ContractorsLast updated
Structural steel frame being positioned during an extension project
Fig. 00 · From one of our projectsStructural steel being positioned during an extension project in Surrey.
Topic
Extensions
Reading time
2 min
Official sources
3 linked
Area
Guildford & Surrey
01 / 06

Gather the approved drawings

Bring together planning drawings, Building Regulations details, the structural design, drainage details and any planning conditions. Give the same latest version to everyone pricing or building the work.

02 / 06

Check access and protection

Note the narrowest width, turns, steps, overhead limits, loading spot and route through the property. Decide how soil, concrete, steel and materials will move without damage.

House extension under construction by A Jones Contractors
Fig. 01An extension under construction: the structure follows the groundworks.
03 / 06

Find services and drains

Plans can be incomplete. Trace drains, manholes, incoming services and overhead cables. Check if who owns a sewer, or a build-over agreement, affects the design.

04 / 06

Check the existing house

You may need to open up small areas to see the existing foundations, floor layers, walls and the wall to be opened. These often decide the order of work.

Completed two-storey brick house extension with bifold doors and new patio
Fig. 02A completed two-storey extension with a new patio connecting to the garden.
05 / 06

Set levels before digging

Agree a fixed reference level, finished floor level, outside slopes, door levels and drain inlets. A small level mistake early can become an expensive problem at the door, patio or sewer.

06 / 06

Plan inspections and records

List the inspections needed before foundation concrete, the floor slab, covering drains, enclosing steel and final sign-off. Photograph work before it is hidden and keep the records.

Before a site visit

Make the survey useful

Five things that let a contractor give you a clearer answer on the first visit, and a more accurate price after it.

Build a site brief
  • Property postcode
  • Photos during the problem
  • Approximate measurements
  • Access width and route
  • Drawings or drain records

Official sources

Check the official guidance

Rules change. Before you decide, check what applies to your property with the source named here, your local council or Building Control.

  1. 01Planning Portal: Building Regulationsplanningportal.co.uk (opens in a new tab)
  2. 02Thames Water: building near a sewerthameswater.co.uk (opens in a new tab)
  3. 03HSE: construction information and planninghse.gov.uk (opens in a new tab)

Found this useful? Send it to whoever is planning the work with you.

How we write guides

Extension Groundworks Checklist

Questions about extension groundworks checklist

Straight answers before you commit. If yours is not here, ask us directly.

01

Can a builder quote an extension from planning drawings?

A rough budget may be possible. A firm price usually needs structural, Building Regulations, drainage, access and specification details too.

02

When should drains be surveyed?

Before the foundation and floor design is fixed, if any existing or shared drain could cross or sit near the extension.

03

Who arranges Building Control inspections?

Agree this in writing. Booking inspections and getting approval are separate from the builder getting the work ready to inspect.

Got a different question? Ask about your site

Your own site

Turn the guide into a plan for your property

Use the guide to work out your first questions. Then check them against your own ground, levels, access and drainage.

Related services

Plan with numbers

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Keep reading

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The next useful step

Get advice for your own site

Share what you have: photos, drawings and rough sizes. We will explain what should be surveyed, designed or approved before work begins.

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