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Double Storey Extension

A Double storey extension adds living space to both the ground and first floor of your home, you get the same benefits on the ground floor as a single extension, but usually without the option of roof glazing. The first floor can then add bedrooms, bathrooms, en-suites etc. A good architect or architectural designer will be able to give you the right advice and options.


If you know where you want the new rooms you need consider how you will access them, the light/ventilation and means of escape. With two stories, the planning limitations must be considered, as the size and scale mean it will have to be designed to fit with its current environment. The regulations are stricter, specifically about fire escape and structure. You need to decide what you want to gain from the build, what you are willing to sacrifice, and how much you have available to spend. Site checks should be carried out on shared boundaries, party walls, mains sewers and if it is a listed building or in a conservation area.

Double rear extensions must too consider the overshadowing and loss of amenity/outlook from the neighbours if near the boundary.

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Design Options

The first design option is the size you will need to build to gain the space and rooms you desire, from there, the internal layout can be explored using the existing structure as best as possible, this will also help save costs. Try to avoid creating inner rooms, as each habitable room will need an opening window. A double side extension will need to look subservient to the house, typically this is done by pulling the front wall back. Clear glazing will generally not be permitted at first floor level within 7 meters of a boundary due to overlooking. Getting a good balance is important, if the sole need for an extra bedroom/larger bedroom is driving the extension, you will have to make good use of the ground floor space too; an open plan kitchen diner, is an option or perhaps a study, utility room or playroom can be considered.

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Planning Permission

Double storey extensions generally need planning permission, as the permitted development rights only permit small sizes. There are a lot of things to consider before submitting a planning application, how it impacts the street scene, does it enhance character, does it have negative effect on the neighbours, does it affect light/privacy/amenity. These are the things the planning officer will be checking whilst making their decision.

Our design technicians will give you the best advice on how to achieve your requirements with the most likely chance of securing planning approval. We will prepare and submit the application on your behalf, then act as your agent, talking directly with the council throughout the application. Click here to see our Planning Permission Guide.

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Building Regulations

You will need a building certificate from a building control body, either local authority or private building inspector. We advise gaining the planning permission before paying for the detailed building regulations drawings, given the additional complexity of meeting the building regulations for a two-storey extension, it is essential that you get the plans approved prior to commencing. These building regulations drawings will then be submitted for a full plan check, amended if necessary, and once approved, they will be the standard that is built too and inspected upon. Our plans will include all the necessary detail such as structure, passage of sound, disabled access, drainage, resistance to moisture, collision, impact, heat loss, ventilation, light, emergency escape and much more. These drawings will be used when the building control officer inspects the site to ensure the builder is carrying out the works correctly. You can generally commence work 5 days from submitting to building control, this is the minimum time due to having to consult the water authority.

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The Build and Builders

Remember, when you finally reach the building stage, only half of the building works will be outside, you should plan and phase exclusion zones with your builder to minimise discomfort whilst the work is ongoing.

With the approved drawings you can now approach builders to provide quotation and price. Check, that any quotation you consider will be written up clearly and with good detail. You will need to know exactly what is priced for, and any additional costs should unforeseen issues arise. We have extensive construction knowledge to able us to assist you and your builder throughout. Use our drawings in line with the quotation, and make sure any additional information we don’t provide such as plumbing and electrics, is agreed in detail before the first fix goes in, otherwise, it will be costly changing things once the initial preparation has been built. Our help and advice doesn’t end once you have the approved plans, we can help you throughout the construction process and visit site if required.

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