Week-by-week extension planner

Planning an extension? Our step-by-step guide and handy checklist ensure your project runs smoothly

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Our week-by-week extension planner is the perfect tool for anyone planning a home extension. Before you get started, have a read through our extension checklist to ensure that you don't forget anything, whether you're planning a home extension and handing it over to a building company or project managing yourself. 

From single storey extensions to kitchen extensions and two storey extensions, our week-by-week extension guide can be applied to any project you have planned for your home. 

Extension checklist:

  • Obtain planning permission, if required, prior to work starting.
  • Submit an application to your local Building Control department.
  • Organise the hire of plant, toilets etc.
  • Compare quotes from trades and let them know if you will be completing any tasks yourself.
  • 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.

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

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

Weeks 3-4: Superstructure

  • Bricklayers will build up the damp-proofing course
  • Drains will be installed and trenches dug for the pipework
  • 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

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

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

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

Week 8: Roof covering

  • Roofing membrane will be laid over the new rafters
  • 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

Weeks 9-10: 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

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

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

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

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

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