Extension planner: a weekly schedule of works for your extension

Our handy extension planner will give you a week by week overview of all the essential stages involved when building an extension

Use our week by week extension planner to stay on schedule: garden room extension wooden
(Image credit: Prime Oak)

An extension planner is a vital tool to make you aware of all the stages involved when extending. Our week by week extension timeline will give you a clear understanding of the schedule or works to consider, so that when you come to extending your home, there won't be any surprises. 

Anticipating everything will not only give you more clarity at each step, but it will also reduce the risk of extra costs and delays (because delays in projects can be costly).

So whether you're extending a house for the first time and have no idea of what's involved, or if you want to refresh your knowledge ahead of starting another home improvement project, we can help. 

Before you get started, have a read through our extension checklist below to ensure that you don't forget anything. And, to get an idea of the types of house extensions you can work towards – even on a tight budget – be sure to read our ideas piece.

How can our week by week extension planner help?

Each extension type comes with its own complications and knock on effects. This week by week extension planner will help anyone planning a single storey extensions, including a kitchen extension. It's also very useful if you are building a double storey extension

If you're looking for cost guidance, use our extension cost calculator, which will help you budget accurately for your extension.

Week by week extension planner checklist

  • Obtain planning permission, if required, prior to work starting.
  • Submit an application to your local Building Control department; find out more in our guide to building regulations.
  • Begin the party wall agreement process if your extension will sit on or affect the party line.
  • Organise the hire of plant, toilets etc.
  • Compare quotes from trades and let them know if you will be completing any tasks yourself.
  • Read up on project managing an extension and decide whether to do this yourself or with professional help.
  • If you’re planning to live on site, arrange the schedule to minimise the impact on daily life.
  • Agree timescales and schedules with trades to avoid delays.
  • Arrange renovations insurance.
  • Let your neighbours know that work is about to start.
  • Arrange access for delivery lorries and decide where skips will be placed.
  • Set up accounts with your local builders’ merchants.
  • Check delivery times for materials and order when needed.
  • Notify Building Control that work is starting.
  • Make space to store materials safely on site.
  • Ensure water will be available for cement mixing and plastering.
  • Make second-fix decisions. such as the positions of lights and sockets, as early as possible.
  • Allow time for plaster to dry before decorating.

Extension planner Week 1: Preparation

  • Make sure there is clear access to the site.
  • Have bricks, blocks and other building materials delivered and stacked close to where they will be needed.
  • If you are project managing, hire a mixer and digger, otherwise your builder or contractor will do this for you.
  • Make sure the site is safe, particularly if you have small children.

Extension planner Week 2: Groundworks

  • Your builders will arrive on site and dig the foundations.
  • Building Control need to visit the site to approve the foundations.
  • If required, reinforcements will be laid within the foundations.
  • Pipework, drainage and services will then be laid within the foundations.
  • Concrete footing will be poured in and levelled.
  • Building Control will need to visit again to approve the footing.

Extension planner Weeks 3 and 4: Superstructure

  • Bricklayers will build up the damp-proofing course.
  • Concrete lintels will be inserted into the brickwork, if required.
  • Concrete lintels will be inserted into the brickwork, if required
  • Sand will then be laid before damp-proofing membrane is put down.
  • Insulation will be fitted.
  • The concrete slab for flooring will be poured.
  • Building Control will need to carry out another inspection.

Extension planner Week 5: External walls

  • Check that lintels, door and window frames and wall ties have arrived.
  • Your builder will create the blockwork and brickwork.
  • Cavity wall insulation will be fitted.
  • Wall ties will be inserted to fix the new walls to existing ones.
  • Lintels for windows and doors will be fitted.
  • Door and window frames will be inserted as the walls are built.

Extension planner Week 6: Internal Walls

  • Internal walls will be built.
  • Make sure you have ordered the windows, doors and roof tiles as these sometimes have lead times of up to five weeks.
  • Check that your carpenter is ready for the following week and all materials are ready, including lead.

Extension planner Week 7: Roof structure

  • Your carpenter will start building the roof structure. Sometimes, prefabricated roof trusses may be used.
  • If you’re having rooflights or dormers, theses will be created and fitted.

Extension planner Week 8: Roof covering

  • Roof battens will be cut and fitted over the membrane.
  • Roof battens will be cut and fitted over the membrane
  • Tiles/slates will be laid.
  • Ridge tiles and valley tiles will be laid, along with finishing details like flashings.
  • Fascias, sofits and verges will be primed, stained and painted.
  • The floor screed will be laid.

Extension planner Week 9: Windows and doors

  • External rendering will be completed, if required.
  • Windows and doors will be fitted into the frames that were put in place when the walls were build.
  • Guttering and drainpipes will be fitted.
  • First-fix carpentry, plumbing and electrics will be completed.
  • Studwork walls will built with door linings fitted and pipes boxed in.

Extension planner Week 10: Breaking through

  • Now is the time to seal off the extension from the rest of the house as things are about to get messy.
  • Steels will be put in place, along with padstones that have been approved by Building Control.
  • Joins will be made good.

Extension planner Week 11: Plastering

  • Walls will be boarded with insulation placed between battens on the existing internal walls.
  • Plastering will take place and must then be left around a week before decorating can be carried out.

Extension planner Week 12: Second-fix

  • Second-fix electrics will be carried out, which means sockets will be made live, switches will be put in place and lights fitted.
  • Second-fix plumbing means taps will be installed and connections completed.
  • Flooring will be laid.
  • Kitchen units will be installed, if applicable. Read the ultimate guide to kitchen design for this part of your project.

Extension planner Week 13: Snagging

  • Report any issues such as leaks, electrical problems, heating system issues, or sticking doors and windows to the relevant trades to get them fixed as soon as possible.

Extension planner Week 14: Get paperwork in order

Once the job is finished and building control have been round to sign off the works, ensure you have all the necessary building regs paperwork present and correct. Keep it somewhere safe – if there are future problems or if you move house and need to prove to your buyer's solicitor that the work was done legally and correctly, it will be useful to know where it is.

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Lucy Searle

Lucy is Global Editor-in-Chief of Homes & Gardens having worked on numerous interiors and property titles. She was founding Editor of Channel 4’s 4Homes magazine, was Associate Editor at Ideal Home, before becoming Editor-in-Chief of Realhomes.com in 2018 then moving to Homes & Gardens in 2021. She has also written for Huffington Post, AOL, UKTV, MSN, House Beautiful, Good Homes, and many women’s titles. Find her writing about everything from buying and selling property, self build, DIY, design and consumer issues to gardening.