How Long does it take to build an extension?

How Long Does it Take to Build an Extension?

How Long Will it Take to Plan & Build a House Extension?

How long does a two storey extension take?

How about a single storey extension?

These are sensible questions to ask, since planning and building an extension to your home will cause you some inconvenience (to say the least) you will want to know how long this is likely to last.

At John Webster Architecture we like to give our customers an understanding (right at the beginning) how long the project might take.

The biggest influence on the length of time this will take will be the budget as this will determine the scale or size of the project.

This purpose of this article is to help you see how long it will take from start to finish to build your extension, this includes the design phase, Planning approval, obtaining a building warrant and the construction time.

You might be surprised at how long this takes!


The Six Stages of a House extension Project with Timescales at a Glance:

*Timescales are based on 25m2 single-storey house extension, if the project is smaller the time can be reduced, if it’s larger then the time will be increased.

How long does it take to build an extension

6 Stages of a house extension project

House extensions – Something to Consider.

It’s a good idea to be informed about timescales before you dive into your building project, as depending on what you have in mind regarding the scale of the project you might want to make arrangements for alternative accommodation during the build, this will depend on your tolerance to living on a building site!

If the project is minor and unobtrusive then this won’t be an issue as the disruption will be kept to a minimum, however if there is a lot of digging concrete out, say in a basement conversion then this will generate lots of dust which might be difficult to live with….worth considering early on in the project.


The timescale of a Building Project


Task & TimelineDescription
1.Feasibility Study-2 weeksDiscuss the Feasibility of the Project, Measured Site Survey, Look at Options and Possible Site Constraints.
2.Design & Planning-12 weeksDevelop the Design, Submit Planning Application.
3.Building warrant-12 WeeksEvolve Drawings to Show Compliance with Current Building Regulations, Submit Building Warrant application.
4.Tender (Select a Builder)-4 weeksPrepare Tender Documents for Contractors, Assess Tenders (prices), Select Building Contractor.
5.Construction-12 weeksConstruction Process on Site.
6.Snagging-8 weeksSnagging Rectified
Total Time (10 months approx.)Project completed


Can we go Quicker Than This? I’m In a Hurry!

There is a saying in motor racing ‘Speed costs Money’ its also true in construction, so here is the question…How Fast do You want to Go?

There are ways to speed things up a little, not a shortcut, but these processes can speed things along a little quicker.

You should be aware though that there is some risk to you by adopting these practices


  • Submit the Building warrant and the Planning Application at the Same Time

Normally the process is to submit a planning application then wait (8 weeks) for approval, once planning approval is secured then a building warrant application is submitted, this is the safest way…one step at a time.

However, if you are in a rush you can submit a building warrant whilst your planning application is being considered…there is some risk for you in as much as, if your planning application is refused or if you are required to submit an alternative design then you will have likely wasted the money it cost to submit the building warrant, but it can result in cutting time.


  • As Above, but Also Get a Selected Contractor onboard From the Beginning.

This can cut additional time from the project as you are bypassing the traditional tender route which does take time.

This involves the contractor being selected at the beginning and having an input very early on in the project, again this is not without risk to you, there is a risk of a delay in the planning process and missing the ‘Slot’ that the contractor had earmarked for the project.

A further risk is not getting the best value for money as the contractor effectively has no competition and can charge however much he wants.


What other factors contribute to how long it will take to Build an extension?

If you prepare to Expect the unexpected then you will be better equipped to deal with delays, the list below highlights some things that have the potential to delay a project, such things as :

  • Inclement Weather holding up work (Summer & Winter)
  • Planning Refusal
  • Poor Ground conditions (not as expected)
  • Having to wait for Trades or Building Contractor
  • Materials arriving on Site Late
  • Changes to the Design
  • Project Growing (Extra work Added as Project Progresses)
  • Unexpected Work Required (eg, rewiring)


Very rarely will there ever be a ‘model’ extension, therefore its best to factor a contingency into your budget somewhere around 10% is a good idea.

Consider also the contractor that you choose, if it’s a small family business, maybe 1 or 2 people it will take longer to build your extension than if you go with a contractor that has 8 employees.

Speed V,s Time

Take this into consideration at the Tender stage, do you want to pay a bit more but get finished quicker or are you happy to have a cheaper price but take a bit longer? (this is definitely worth considering if you are moving out and paying rent somewhere else)


Timescale and Cost for a medium size house extension

Real life Example of a single storey extension, approx 34m2, this house extension incorporating a Lounge, utility room, and a shower room took 10 weeks to build and cost £59,569 (including all fees & VAT)

The total timescale for this project from the very beginning all the way through the design & construction stages was 10 months.

How much does it cost to build a house extension

How much does it cost to build an extension



Its safe to say that it’s not one size fits all when answering the question, How Long Will it Take to Build a House Extension? But there is a tried and tested process that if followed won’t let you down.

The best piece of advice you can follow is to give yourself plenty of time, you are preparing to spend your hard earned money, you’ve probably been dreaming about that kitchen extension for years….so don’t rush if you don’t have to, take your time, relax and enjoy it.



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