Cost of Extension

Cost of Extension

>> Scenario Architecture and house extensions

In the era of “don’t move, improve”, Scenario finds itself among the top residential architecture studios in London for high-end home extensions. We know that the cost of extensions in London can be limiting, so we do our best to ensure every penny you spend translates to a high-functioning, high-spec package. Our distinctive and spacious house extensions – from simple single-storey extensions to larger side-return extensions, rear extensions and basement extensions – give new purpose to period properties and raise the bar for what a small architecture practice can achieve.

We established Scenario in 2007 with a vision to maximise living spaces to their greatest potential on a practical, reasonable budget. Our boutique practice takes a considered, efficient approach to our clients’ needs and desires, making the cost of building an extension accessible.

Our landmark project Scenario House, an East London Victorian home with a unique, light-filled side-return extension, was covered widely by the media and shortlisted for several prestigious architecture prizes – including the 2018 RIBA London Awards. It demonstrates our innovative, economical approach to opening up period properties for 21st century lifestyles.

Tell us about your house extension

Cost of Extension

Edwardian house extension in London

Cost of Extension

Glazed house extension in London

Cost of Extension >> Your house extension project

Starting your house extension

If you plan to tackle a house extension in London, we’re happy to help, whether you’re planning a single-storey extension, side-return extension, basement extension or rear extension.

To help save on the cost of extensions and understand each stage of the expansion process, we’ve created a brief illustrated overview.

Most house extension projects in London require planning permission from the local council. By securing planning permission quickly and successfully, we can help keep down your cost of extension.


TIP: Discover if your chosen architect has had success steering planning applications through your local council. Visit the “planning applications” section of your council’s website and enter the architect’s name in the search criteria.


To help you save on your house-extension cost and understand what it takes to obtain planning permission in London, we’ve created this helpful handbook. Download it here.

This handbook should suit anyone requiring consent from the local council to alter a home. It reviews the planning-permissions, protocols and costs of building an extension and strategies for successfully navigating the process, based on our own extensive experience.

Cost of Extension >> Scenario Architecture advice on cost of extension

Advice on the cost of extension, and working with Scenario Architecture

Scenario is a boutique architecture studio focused on expanding and improving homes across London and beyond. Through our bespoke architecture service, we tackle projects of every scale and complexity, from modest single-storey extensions to double-height extensions, side-return extensions, basement extensions and rear house extensions.

The cost of extensions varies. This will depend on the scale, design, exterior materials and interior finishes of your extension. Before designing an initial concept for our clients, we discuss their big-picture aspirations and daily requirements.

When we budget the cost of extension on any home, we must consider the different types of extensions. Extending upward with a loft extension, for example, is often significantly cheaper than a side-return extension and rear house extension and most definitely a basement extension.

We understand our clients’ desire to understand the cost of building an extension before committing to the process. For a single-storey extension – be it a side-return extension or rear house extension – we allow between £2,000 and £2,500 per square metre, depending on finishes. These figures can also apply to renovating the existing areas within a house.

When it comes to loft extensions, it’s best to stay away from square-metre calculations as these may be confusing and misleading due to varying head-height requirements, kitchen and bathroom requirements and roof repairs. Generally we allow between £35,000 and £55,000 for loft extensions, depending on finishes.

Excavating a new basement is a great way to add significant floor space to your house with limited planning regulations. However the cost of extension per square metre is, by far, the highest in a basement. We allow between £3,000 and £3,500 per square metre, subject to finishes.

Early adopters of the latest drafting and building technologies, we use innovative 3D design and visualisation tools to bring down house-extension costs. Our experience has shown that real-time visualisations and virtual reality are extremely efficient tools for choosing finishes, fixtures and fittings, and simulating natural light.

We use 3D building information modelling (BIM) technology to produce reliable construction information, so all our project data comes from an accurate, coordinated 3D model. Using this cutting-edge technology collaboratively with consultants and contractors is proven to save on home-extension costs.

A Chartered Institute of Building case study featuring a Scenario project demonstrates the positive effects of this advanced technology on home-extension costs.

Scenario Architecture is a RIBA Chartered Practice. We comply with the strict criteria of the Royal Institute of Chartered Architects, covering insurance, health and safety and quality-management systems.

Start your house extension

Talk to us about your project. Enter your details below and we will contact you.

Cost of Extension >> In our clients words


We wanted to renovate our house in a conservation area in central London. Given this involved a complete demolition and new build with an extra floor on top, getting planning approval was always going to be tricky. Scenario did an amazing job on the new house ‘envelope’ and throughout the planning phase. We couldn’t have wished for better from them and having succeeded in gaining planning approval owe them a very big ‘thank you’.


Scenario designed a kitchen extension for us, and we are delighted with the results. The process was well organised, planned and delivered, and the whole team were a pleasure to work with. I would highly recommend them for their design, planning and project management skills.


Worked with these guys on the internal development of our office. From start to finish they were great. They got what we wanted first time and really made working with them very easy. Their aftercare has been great too helping us deal with something that they were not involved with in the first place. Will highly recommend them to anyone.

See all Google reviews