Trimble Architects

RIBA Architectural Services

Phone Number: 020 8538 9303

Mobile Number: 07785711635

Are you looking for double storey extensions architects in London? Our RIBA local architect services works throughout Hounslow, Twickenham, Richmond, Kingston Upon Thames, Teddington And Throughout London.

Double Storey Extensions

You can gain extra space and add plenty of value to your property by building a double-storey house extension. Numerous homeowners across the UK consider a two-storey rear extension or wrap-around extension instead of a one-storey; no matter the option you select, you'll only require one set of footings and a flat roof pitch.

You can achieve the most value from your build by providing extra space for bathrooms, shower rooms and master bedrooms through a house extension in central London or South East London. 

There are multiple options of whereabouts on your property that you can have your extension built, including a loft conversion or basement extensions; however, the best location tends to be a double-storey rear extension.

It's excellent to understand that before carrying out proposed work with most architects throughout London or at Trimble Architects Ltd, you must consider utilising your potential available space, whether you wish to curate a kitchen downstairs or a new living area or a bathroom space. 

Once you've figured out the use of your brand-new extension space, you can begin gathering the right London architects to curate the desired living space, bedrooms, new kitchens or bathrooms under planning conditions to ensure they blend in with the rest of your property.

If you wish to seek advice on how best to interpret new space in your home, contact us today for further information and a free site visit and consultation. Double-storey extensions are two-storey installations that extend the length or width of your house or living space across two floors, one lower and one upper floor, so that you may have a second-level floor and one at the ground floor level.

A two-storey extension allows you to enhance your living space to accommodate various happenstances, whether a growing family, a home office, an at-home gym, more space to store belongings, or additional bathrooms to free up traffic on busy mornings. 

Double-storey extensions give a family or household of individuals plenty of opportunities to provide more space for life to evolve or to increase the value of the property for the future.

What is a Double Storey Home Extension?

Double-storey house extensions sometimes referred to as two-storey extensions, are the lawful development of new space onto your existing house with an additional floor, allowing for even more structural design opportunities and storage space.

Some homeowners may already have single-storey extensions installed into their houses and wish to add another first-floor extension over the current one, which creates a double-storey extension and, thus, much more space.

The two-storey extension appeal comes from creating another set of upstairs and turning those additional spaces into whatever you desire, whether a new bedroom, a larger kitchen space, another bathroom, or a spare room for storage. 

Double Storey Extensions London

Adding a Double Storey Extension to the Side

For those that don't live inside terraced houses or semi-detached houses, it is entirely possible to add a double-storey extension inside your home through the means of your permitted development rights as long as what you wish to do qualifies with the regulations. If not, you may have to begin crafting a planning application for planning permission.

However, the good news is that you can add two-storey extensions on either side of your existing property to make your household much wider. An enlarged house will allow you to expand the space in your living area and kitchen or include any additional bedrooms.

On the other hand, if you have plenty of additional space on one specific side, you may wish to build a double-storey side extension, creating a new dwelling space to enjoy. 

Adding a Double Storey Extension to the Rear

Homeowners often begin to have their homes extended out towards the rear, and then, if they can get the funds, they may continue to build. In the UK, you can find plenty of houses with spacious back gardens, which will become the land you can build on if you wish to increase the overall size of your dream home.

One of the most significant advantages of a double-storey extension at the rear (backyard or garden space) is that it cannot disfigure or adapt the facade of your home or its front view, which is guaranteed to please the local councils and authorities.

Many houses across the UK tend to be built wider instead of deeper, meaning that the final result of your building is usually more square-shaped with a range of neat, traditional-shaped rooms. 

Two-Storey Extension Ideas

There is a broad range of different two-storey extension ideas that you can select from that will enable you to curate additional space that will work for you, your family and even guests. 

wo-storey extensions allow you to transform the upstairs into a guest or child's bedroom or even two on top of one another, giving you the extra space you'll need to make your house feel more like a home with a purpose.

The two-storey extension allows the interior layout of a spacious upstairs and downstairs area that offers two new rooms or spaces.

You can add another bathroom to free up the bathroom traffic you may experience during busy mornings. The downstairs can be utilised to create an excellent living space with even more room for friends and family to gather during get-togethers.

By investing in double-storey extensions, you can choose a bespoke design for an open-plan kitchen and select brand-new appliances best for entertaining large-scale family meals.

You have plenty of choices when incorporating a combined dining and living area with gleaming sliding doors or bi-folding doors open to a beautiful garden or patio.


A space that lets in a great deal of natural light is bound to feel bigger and allows you to experiment with all the ways you can use the space. Investing in a double-storey garage extension is another option you can choose, giving you plenty of space to free up the upstairs and at the side of your garage conversion.

Such is a typical and popular form of double-storey extension; however, it doesn't have to be placed on the side rear of your home. You can utilise it for any wasted space above your garage to spread apart your belongings or create an entirely new room with a different purpose. By installing a two-storey extension, you can ensure your property is more competitive within the housing market to increase its value.

If you ever decide to move house, an extension of this scale will allow you to market your property at maximum value. 

Double-storey extension cost?

All average construction costs in most industries have risen exponentially after the COVID-19 pandemic of 2020 and 2021, much like the cost of everything else. 

The average cost of double-storey extensions in the UK varies regarding the location you're based in. Its prices range from £2,000 to £2,500 per square metre, yet you must remember that the finishes you select will also be factored into the final double-storey extension costs.

Much like the other capital cities of the world, London's average building cost is a little more expensive, with figures that range around the £3,000-£3,500 per sqm mark. However, throughout London, extra space tends to be of more value and higher prices, as it is few and far between, which is why the value is bumped up to around £7,000 per square metre. 

Frequently Asked Questions about Double Storey Extensions

You'll find that the cost of a double-storey extension project per sqm will usually be slightly higher than the cost of single-storeys. However, it may help to know that when you expand multiple floors simultaneously, you can save money instead of spending plenty on separate projects. 

A general multi-storey extension in London will cost around £1800 square metres; however, you must remember that the project's cost will vary based on the exterior materials, the design and the finishes you opt for.

To summarise, let's say that a double-storey extension of around 4m by 5m and a total of 40 square metres between the two floors could cost you around £53 for its build costs. 

Such is without additional professional architects fees, planning application fees, structural engineer fees, roofing costs, interior fit-outs or VAT. Here we'll provide an idea of the professional and planning fees you must consider during the planning process for your double-storey extension.

  • Administration Fees are 1%
  • London Architects' average fees are around 10%
  • A Structural Engineer will cost at least 4%
  • Surveyors' fees are 3%
  • Your Contractors will take up 30%
  • VAT tends to be around 20%

Additionally, planning fees for a two-storey residential extension in London, England, will cost upwards of £206. 

However, it's good to ensure you're aware of the building control charges, as these are usually depicted on the size of your extension, meaning costs can vary between £200-£900, whether you select 10m squares or from 80-100m squares. 

For further information, contact us; we're a design and build company that can provide free quotes and estimates. 

For those considering a double-storey extension for their household, whether it be to add space to your existing building or increase its value, you'll have to inquire about permitted development. 

Some household extensions are regarded under permitted development; however, there are limitations and planning restrictions, and only so many aspects can be completed until you require planning permission from your local planning authority.

For example, it can be more challenging to obtain approval if you're based in conservation areas like a national park or if you live in a listed building. For example, you and your extension builders can construct your two-storey extension at the rear of your existing property, yet when in this position, you must ensure that it cannot be any taller than the existing roof's highest point.

With a rear extension, you cannot extend beyond the rear wall further than 3m. Additionally, you must ensure that the materials of your original house build match that of the extension building, and it must be approximately 7m away from your household boundary. Extending too close to your boundary, you'll need planning permission, and we would encourage you to enquire about a party wall agreement.

It would be best if you made sure that the openings of your side rear extension are obscure-glazed and non-opening; otherwise, they could obstruct your neighbouring windows or neighbouring properties. A discussion with your neighbour is paramount during any new build or household improvement so that you can clear the air, get approval and make them aware of the duration of construction.

Finally, if the roof on your brand-new extension is connected to your current roof, you must subtract the extension roof volume from the loft conversion volume allowance you may possess. 

Many often question whether a two-storey will add value to their property, and the answer is most definitely yes. Adding footage will boost your property's value on the UK market, as it allows a family or more significantly-sized households so many possibilities to get creative and implement the rooms they need or desire. There are opportunities to store their belongings in unique and practical ways instead of dumping things in boxes in sheds or garages.

Plenty of research carried out by Nationwide suggests that home extensions and improvements across the UK can add prominent value to a property. The data showed how ensuites and double bedrooms could increase the overall value of your home by 23%.

If you have the budget to invest in a brand-new household extension, we highly recommend doing so, especially if you plan on selling your home in the future. Any significant home improvement will draw in potential buyers, and it may persuade them to purchase your house. 

Firstly, it is much cheaper to opt for a two-storey extension considering the amount of extra space you'll gain, as many homeowners typically spend on green roofs and foundations is often the same regardless of whether you select one storey or two. Another reason why two-storey house extensions are so greatly popular is that you'll gain plenty more practical room.

You can convert this space into virtually any room to fulfil any purpose; for example, for those planning on having a family or another child, you can curate a bedroom with a downstairs bathroom or a study to accommodate the needs of a much bigger family. There are so many possibilities with a two-storey extension; you can create playrooms, at-home gyms, add guest rooms and many other rooms. 

While designing a double-storey extension, you must ensure they meet all the rules that come along with permitted development rights. 

Otherwise, you will be expected to go through the process of applying for household planning permission so that your two-storey extension can proceed. Planning permission isn't always necessary for every two-storey build unless there are features that surpass the regulations, such as the length and width passing the length or width of the original building.

The most significant downfall of realising your dream extension plan requires planning approval is that it tends to take far longer to get to the point of construction. You'll have to assess your plans and deliberate with planning consultants and trusted architects in your area to consider whether the local council will take to your extension plans and allow you to implement them.

Your architects will thoroughly check to see whether your building regulation drawings, structural calculations and floor plans comply with the local policies. You must ensure you don't obstruct your neighbour's view or the layout of the street or neighbourhood where you intend your extension to be built. 

In short, your planning consultants and our architects at Trimble Architects Ltd will do the utmost to help develop your extension designs and ideas, alongside preparing solid planning drawings that reflect your desires and accurately match the requirements.

To justify why you should receive planning permission for your two-storey extensions, we'll help you curate Design & Access statements that are filled with the details of your new build in hopes of convincing your local authorities. We have highly qualified and insured professionals that have worked on numerous extension projects before; we cannot guarantee that you'll receive approval every time.

However, we'll work hard to do what we can to adapt your plans to ensure they fit the building standards. 

Trimble Architects

Based in Twickenham

South West London

Contact Us

If you require help and advice from our double storey extensions architects get in touch today. Trimble Architects are based in Twickenham and work across south-west London.

Get in touch