Before you get started, have a read through our extension checklist to ensure that you don't forget anything.
- 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 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