Open plan living space at Strathyre Place, Falkirk

So, how long does it take to design and build an extension to my home?

In the initial stages of planning a project to alter or extend your home, it is very common for Clients to ask ‘How long will all of this take?’ In order to understand an overall timeline when considering a project to alter and extend your home it is important to understand each step in the process. This article is intended to provide homeowners and first time Clients with the information they need to understand the steps, what to expect at each stage and allow plans to be made accordingly. Whilst the timeframes will vary somewhat from one project to the next, depending on the overall scope of the work, the following can be used as a typical guide for a project to alter and extend your home.

Typical domestic procurement process and timeframe. © Taylor / Wilson Architects.

Does the construction industry have a recognised system of working?

The construction industry as a whole and across all professional disciplines (Quantity Surveying, Structural Engineering, M&E Engineering & Contractors) works to a sequence of work stages known as the RIBA Plan of Work published by the Royal Institute of British Architects. This approach to procurement of construction work is utilised virtually without exception across the industry and allows for a range of different procurement methods.

A copy of the RIBA Plan of work can be downloaded here.

Commercial projects can be procured in a variety of means to suit the Client’s or stakeholders requirements. In simple terms the two widely used procurement routes are known as ‘Traditional’ and ‘Design and Build’. These routes offer different priority in the management of time, cost and quality and are discussed with Clients on a project by project basis to suit the particular project’s priorities.

That’s all good and well Mr Architect, but surely there is a simpler way for smaller projects?

Yes indeed! Domestic projects tend to follow a more similar route and timeframe. Domestic projects work on a simplified ‘traditional’ procurement methodology, where a Client appoints an architect to develop a design, work alongside a Quantity Surveyor, Structural Engineer to develop cost plans and structural design information, obtain statutory approvals and tender the project in the marketplace, ultimately resulting in appointment of a contractor to deliver the project.

The Royal Incorporation of Architects in Scotland recognise this approach in their standard forms of appointment for small projects, known as RIAS ASP/2018. The work stages set out in this appointment are as follows:

RIAS Stage 1: Preparation and Brief
RIAS Stage 2: Initial Design
RIAS Stage 3: Develop to Planning
RIAS Stage 4: Develop to Warrant
RIAS Stage 5: Construction Info
RIAS Stage 6: Tender
RIAS Stage 7: Contract Administration
RIAS Stage 8: Post Completion

Contemporary brick, zinc and glass extension to detached family home in Muirieston near Livingston. The project provided a self contained 1 bedroom ‘granny annexe’ to support multi-generational living.

RIAS Stage 1 : Preparation and Brief

During this stage we will meet with you to understand your project specific requirements. We will also survey the property or arrange for a survey to be carried out by a land surveying company, depending on the nature of the particular project.

We will then prepare as existing drawings, as a record of the existing land or building. These drawings are then used as the basis to develop design proposals. Your architect will develop the project brief and key aims of the project and confirm this to you in writing.

Typical work stage timeline: 2-3 weeks from appointment.

RIAS Stage 2 : Initial or Concept Design

We will prepare some initial design options and meet with you to review. Typically we start this process with three options as this allows an approach of ‘do minimum’ to be tested alongside a ‘do maximum’ and a middle ground solution which seeks to rationalise the important aspects of the brief and offer an initial understanding of the scope of work under consideration to inform the budget for construction work.

Once the principles of the design are agreed, we prepare 3 dimensional models of the project to explore the design in 3 dimensions, materials, relationships to neighbours, aesthetics, overshadowing and so forth. This is a good time of engage the services of a Quantity Surveyor to prepare an initial cost plan or professionally prepared budget, as this offers opportunity to realign the project scope and budget prior to making applications for statutory consents.

Typical work stage timeline: 4 weeks from instruction to proceed.

Example concept stage visualisation for project in the Elie and Earlsferry Conservation Area.

RIAS Stage 3 : Develop to Planning

At this stage the task is finalising the schematic design and any queries outstanding from concept stage. Drawings and outline specifications are produced in sufficient detail to allow applications for Planning Permission (and Listed Building Consent where applicable) to be submitted to the local authority. Your architect will prepare and submit the planning application and act as your agent in administering queries arising from the local authority and keep you abreast of progress.

On projects which involve a new build house, a design statement is also likely to be produced to provide further information on the design approach and how local planning policies have been considered and incorporated into the design solution.

It is important to remember that once submitted, local authorities in Scotland have an 8-week statutory period to process domestic planning applications from the date of validation. Every local authority will publish all planning applications publicly on their website. When published the information on the application timelines and target determination deadlines are made publicly available, which means you can check for yourself. Your architect will let you know when the application has been validated and is visible online. Whilst some local authorities are better than others at achieving the deadlines set, it is the case that the statutory period for householder planning applications is 8 weeks and the online planning function allows transparency which is helpful for all involved.

Typical work stage timeline: 4 weeks from agreed concept design to submission of planning application, typically 8 weeks from submission to determination.

Typical planning stage drawing for a new garden room pavilion extension to a detached property in the Arnothill and Dollar Park Conservation Area.

RIAS Stage 4 : Develop to Warrant

The process of developing the design towards an application for Building Warrant involves developing your approved planning stage design in technical detail. This will, on virtually all projects, involve working alongside a structural engineer. Your architect can help you to appoint a structural engineer if you wish.

The designs are developed to describe the construction methodology, structural arrangement, heating, drainage, services requirements and so forth. The design will also include information on compliance with the Building Regulations.

A copy of the current Scottish Building Regulations for domestic properties can be downloaded here.

Once the technical designs are completed in sufficient detail to evidence compliance with the building regulations, your architect will then prepare and submit your building warrant application and act as your agent in administering queries received from Building Control.

As at planning stage, local authorities in Scotland have an 8-week statutory period to process a Building Warrant application for a domestic project. It is similarly the case that the performance of local authorities in achieving these deadlines, which are set by the Scottish Government, vary from one council to the next. In our experience, our own local authority, West Lothian Council, perform favourably when measured against other councils.

Typical work stage timeline: 6-8 weeks from Client instruction to proceed to submission of application, 8 weeks statutory timeframe to Building Warrant approval.

RIAS Stage 5 : Construction Information

The purpose of the construction documents is to develop the building warrant information to provide all of the information a contractor needs to price the project, to define the Client’s preferred choice of Building Contract and ensure that a clear payment mechanism is established and understood. Items like finishes, kitchens, bathrooms can be developed during this work stage in greater detail to allow liaison with the Client’s preferred suppliers and chosen products to be specified.

Where the Client wishes to choose these items later in the process, they can be defined as ‘Client Supplied’ or ‘Client Direct’ and the contractors will understand what aspects of the work he is asked to price and those which remain the responsibility of the Client.

Typically on a home extension project your architect will prepare further 1:5 construction details, develop a works schedule for use by pricing contractors and advance the tender particulars, material specifications, finishes information, client supply items and component drawings as appropriate and sufficient to accurately define the scope of works to be priced by tendering contractors.

Typical work stage timeline: 2-4 weeks from instruction to proceed (this period will typically overlap with the development of the RIAS Stage 6 Tender information on domestic projects to alter or extend an existing house).

Example construction details prepared to support a Building Warrant application for a project in West Calder.

RIAS Stage 6 : Tender

During tender stage we will have compiled a list of contractors, in discussion with you, who may be interested in pricing your project. The full set of documents will be compiled and released to the marketplace to allow the project to be priced. Your architect will take receipt of the tender returns and compile a brief tender report to allow any negotiations or clarifications to be obtained.

The conclusion of the tender process arises where the contractor is appointed, start date agreed and the Standard Form of SBCC / JCT Building Contract is signed.

Typical work stage timeline: 2-4 weeks from Client instruction to proceed to release of tenders to market, 4 week tender period for contractors to price.

RIAS Stage 7 : Contract Administration

During construction, the architects role is to administer the terms of the Building Contract. Often, lay Clients refer to this as ‘Project Management’, but that description is inaccurate in that the role of Project Manager is that of your appointed Main Contractor in domestic construction.

In administering the terms of the Building Contract, your architect will inspect the works at pre-agreed intervals suitable for the scale of the project being undertaken, monitor variations to the contract, answer technical queries arising from the Contractor and ensure the terms of Building Control’s Construction Compliance Notification Plan are being addressed by the appointed contractor. We will complete the valuation procedure at the agreed intervals and certify the appropriate payment to be released at each stage to the contractor, whilst adjusting the contract sum to suit pre-agreed variations. Most importantly, this ensures you remain in control of your spend during construction. The contractor is only paid for variations that are agreed with both Client and Architect in advance of works being implemented on site.

We will provide forecasts at each stage of the project, for the remaining payments to be released to completion. This will allow you to understand the current position, plan for any future variations and understand the timing of payments.

Typical work stage timeline: 12-24 weeks is, in our experience a typical range of timeframes for a domestic extension project to be constructed.

RIAS Stage 8 : Post Completion

The post completion stage is designed to allow a period of time for you to live in your newly refurbished or extended home, whilst retaining a percentage of the agreed contract sum. At the end of the pre-agreed defects period and when all defects have been remediated, there will be a final inspection carried out and the retention money will be certified for payment to the contractor. This is known as the Certificate of Making Good Defects and confirms that the contractors have repaired all defects reasonably arising from the construction works.

Typical work stage timeline: Typically 3-6 months post completion subject to the form of contract used and agreed defects period.

Zinc, glass and render extension to a Linlithgow home designed and constructed using the methodology described in this article.

Summary

So, in summary and to answer the original question ‘how long does is take to design and build an extension to my home?’

You can reasonably expect a ‘design’ or ‘pre-construction timeframe’ in the 6-12 month range. You can make decisions to prioritise your risk appetite against your need for speed! We can advise you how to do this to achieve the right balance for you.

A typical domestic extension construction timeframe is in the 3-6 month range for a typical extension. This will be longer, typically 9-12 months if the project involves construction of a new home (or is an especially large extension). It will similarly be shorter if your project involves only a garage conversion.

Considering a project of your own?

Please get in touch to arrange a no obligation initial consultation.

How long does it take to design an extension to my home?