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Design to Construction - How long does it take?

Updated: Mar 1

closeup of hand drawing

We are frequently approached by prospective clients who are looking to start the build process within the next few months. Unfortunately, things are not so simple. This blog entry aims to give homeowners a broad understanding of the design process and other factors that contribute to the timelines of a typical single-story rear extension project.

Preparation & Brief

Primarily, an architect or designer should always establish your brief. This process should begin with an initial discussion about your requirements and a site visit, which usually results in a provisional set of sketch layouts and diagrams. A measured survey of the property is required to create these preliminary sketches. Some architects conduct the survey themselves, while others hire measured survey providers. This information serves as the foundation for a more in-depth discussion of your specific needs, requirements, and vision. The goal is to create a cohesive initial brief from which to work when moving on to the next design stage.

Time check = 2-4 weeks

Site visit, measured survey and sketch layouts

Concept Design

The concept design stage takes the initial brief and turns it into more detailed design proposal, which frequently includes 3D visuals. The goal is to focus on your needs while providing design ideas that meet, if not exceed, your initial vision. The use of 3D visualisations is critical in communicating how the proposals will look and feel. This is a very effective design tool for assisting in the visualisation of a 2D plan.

Time check = 3-4 weeks

Concept designs, design meetings and drawing iterations

Developed Design & Spatial Coordination

This stage examines the preferred design in greater depth by testing it against Building Regulations and considering construction methods and materials. For this stage we recommend bringing a Structural Engineer on board for the provision of a structural design and coordination. The goal is to develop a scheme that works for you and can be used to inform a Planning Application.

Time check = 3-4 weeks

Developed design & planning application

We are now 8 – 12 weeks in.

Planning Stage

From validation to determination, a Householder Planning Application takes 8 weeks (although this can vary depending on the workload of the Local Authority). This frequently halts the process for two months due to the risk of continuing without planning approval. This pause is, of course, optional, and some clients prefer to proceed at risk in order to save time.

Time check

Validation = 2 weeks

Planning determination period = 8 weeks

Technical Design

We have now received planning approval, what next…? This stage takes the approved scheme and expands on it. A technical set of drawings is created and coordinated with the final structural design, which includes material and performance specifications. The end result of this stage is typically a tender 'package' that contractors can use to provide a detailed quote. This will also serve as a 'Building Regulations package' for to inform a Building Regulations application.

Time check

Production of technical design information = 4-6 weeks

Tender period = min. 4 weeks

We are now 26 – 32 weeks in including planning determination and tender periods (provided they meet the statutory 8 week deadline)

Building Regulations Application = 5 weeks (this can run its course during the tender period). This can be reduced if you opt for a Private Inspector Service over the Local Authority Building Control.


Once you have chosen your preferred contractor it is now time to agree the cost and start date and sign the Building Contract. Clients often wish to manage the project themselves from this point, however there is value in appointing an architect or other suitably qualified building professional to do so on your behalf. The value is in tracking progress, monitoring workmanship, identifying cost increases/savings, and ensuring that work is completed in accordance with the contract.

Having someone with experience in construction project management and administering Building Contracts can often make the project run more smoothly and reduce costly delays as issues can be resolved more quickly and efficiently.

A typical single storey rear extension can take approximately 13 weeks to complete.

Total Time = 39 – 45 weeks or approximately 10 months.

This time period is of course a broad estimation of a step-by-step process and is affected by client feedback and consultant response times as well as Local Authority and Building Control determination periods (they sometimes take longer) as well as project complexity and resource availability.

Advice & Recommendations

We believe that each project and client is unique, so we always try to schedule a visit to discuss your needs in person before providing you with a fee quote. Many designers will gladly provide you with a quote based on a two-line description; however, our advice is not to be swayed by price alone; instead, consider what is included as part of the service, their credentials, and insurance status. Fixed-fee, pre-visit quotes are frequently accompanied by a quick, low-cost service, which can result in compromised quality and attention to detail. A reputable professional should be happy to share their reviews, qualifications, and evidence of insurance, so do not feel uncomfortable in requesting this information for your own protection.

If you are thinking about starting a project in the near or not-so-near future, it may be worth considering commencing the design, planning, and approval process sooner rather than later due to the necessary time it takes from design to approval. There is value in having a project's "paperwork" completed and ready to go for when the time comes to appoint a contractor. Notable constraints would be those related to statutory approvals. You have three years from the date of your planning approval to commence works. Work must begin within three years, but it does not necessarily have to be completed within that time frame.

Seeking advance approval is also advisable for gaining Building Regulations approval. This strategy also protects you from any updates to Building Regulations that may be issued during this time period. With this in mind, you can begin the design work, go through all of the necessary channels, and have a complete set of information ready to go which remains valid for three years.


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