How long does an extension take?

This is one of the questions we are asked most frequently, so we thought we would go into a bit more detail about the timelines of home extensions. Here at Home Tales, we specialise in home extensions around London & Brighton. All the timelines and estimates that we give below align with our experience within design and planning, and with our recommended builder.

Architectural design

This is the first stage of your home extension journey and perhaps the most exciting! Here at Home Tales, we offer unlimited amendments to your floorplans so you able to experiment with design options. This helps to secure your decisions from an early stage which helps streamline the process. If you change your mind on the design at a later stage it can cause delays as you might need to adjust the structural calculations or go back into planning. From the date of the survey, it takes approximately 2 weeks to get initial plans back to you. Amendments are then undertaken within 1-2 days. We can work as quickly as you like and adapt to your timelines. If you want to take your time you are free to do so. Some of our clients take weeks / months to decide on their design, others like to get into planning within the week!

Planning permission

If you need planning permission or a permitted development certificate, it generally takes 8 weeks for your local council to issue a decision. Householder applications and full planning permission are 8 weeks by default. Permitted development does have a 5 week ‘target’ deadline but it’s rare they are achieved, and they usually default to 8 weeks as that is the statutory maximum time. We check in with your case officer at regular intervals to minimise the risk of delays.

Structural calculations & Building regulations pack

Your structural calculations are part of your building regulations pack (BPR). This takes 2-4 weeks to produce. The reason is takes some time is the structural calculations is a pretty hefty document and it takes time to create the calculations and ensure everything passes regulations. This pack can be started during the 8 week planning window if you wish to save time.

Party wall

Party wall might be required if you are extending or carrying out extensive internal refurbishment (ie. wall removals which require steel, or chimney removals). This process generally takes 8-12 weeks but it can take longer if your neighbours request additional information. Party wall is valid for 1 year so we would recommend waiting until you have a build start date in mind before commencing with this one. Lots of clients opt to begin party wall while planning is on-going as both are lengthy processes.

The Build Phase

For a typical ground floor side return extension OR a rear extension, the build takes about 12-16 weeks to get the room watertight. This means doors and windows are installed, the plasterwork is finished, and plumbing is ready for final fix to take place. The decorative works vary a lot depending on the finishes you select. For example, small mosaic tiles are much more labour intensive (and therefor take more time to install) then large floor slabs. We can always give you an indication of time before you commit to a design or material so don’t worry. Other items might affect the build duration too. For example, if you select a bespoke all-glass roof then the frame of the roof needs to be built before the glazing can be ordered. If you select Velux windows, then these can be ordered and ready on-site to install as soon as the roof is built.

If you are undertaking a wraparound extension (side and rear extension) the build will take around 16 – 20 weeks to get watertight. There is more work that goes into the wraparound extension including a more complex steel structure to arrange. The room size is also (in general) larger so it’s longer than a simpler side return or rear extension.

A single dormer loft conversion typically takes 8-12 weeks to get watertight. An l-shape dormer loft conversion will take 10-14 weeks. You can allow an extra 2-4 weeks for labour time to fit bathrooms or install carpets etc.

If you are undertaking a double project (for example a ground floor extension and a loft conversion) you can gain some efficiency in doing the build together. They cannot start in unison as the loft requires a scaffold which interrupts the start date of the ground floor extension. As soon as the scaffold comes down the ground floor extension can be commenced.

If you have any questions on timelines or anything else we would be delighted to help. Call us on 0207 043 2378 or email us at You can book a consultation directly via our live diary here. 

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