A two storey extension can be a cost effective way of gaining maximum floorspace for your property, without eating too much into your garden. It will also mean that your house isn’t bottom heavy, which can be an issue with some large single storey extension projects where they have a huge living space but a lack of sleeping accommodation above. This short guide to two storey extensions will cover the two most important points to get you started: Do you need planning permission for a two storey extension? and How much does a two storey extension cost?
Two storey extension by Oliver, an architect on Design for Me. Click the image to see his full profile and shortlist him for your project.
How much does a two storey extension cost?
As a basic rule of thumb, a two storey extension will cost around 50% more than a single storey extension. Read about extension costs per square metre in our guide here: https://designfor-me.com/cost-planning/renovation-and-extension-cost-per-square-metre/. Based on this guide a (3x6m) two storey extension would cost:
- TYPICAL HOUSE-BUILDER EXTENSION – £55,000 (NO PURPOSE MADE JOINERY, STANDARD WINDOW SIZES, STANDARD BATHROOM SUITES ETC)
- MEDIUM-HIGH ARCHITECT DESIGNED EXTENSION – £70,000-80,000+ (NICE CLADDING, LARGE EXPANSES OF GLASS, INTERESTING BATHROOM / KITCHEN DESIGN)
These figures are a very basic starting point and you should not base your expectations for your project on these alone. Speak to an architect about your specific property and design ideas to get a better understanding.
Do I need planning permission for a two storey extension?
Two storey extensions do not require planning permission, if they fall within permitted development guidelines described below.
How big can I build a two storey extension without planning permission?
- MAXIMUM HEIGHT: Firstly the eaves and pitch heights must be no higher than those of the existing house. However, if the building is within two metres of a boundary, the overall maximum eaves height is restricted to 3m. The roof pitch should match the existing house as much as reasonable practicable.
- FOOTPRINT: Under permitted development rules, you can extend up to three metres from the original house* but it must be more than seven metres from the rear boundary (opposite the rear wall). Any extensions to the original house*, sheds or outbuildings should not exceed more than 50% of the total area of land around the house.
- MATERIALS: The materials used should be similar in appearance to that of the existing house.
- LOCATION: Two storey extensions to the side or front of the original house are not permitted development.
- OTHER: No verandas, balconies would be allowed without planning permission. Any upper floor window in a side elevation must be obscured glazing and non-opening (unless its more than 1.7m from floor level internally).
*original house means as it was built or as it stood on 1st July 1948.
There are some specific restrictions regarding your particular property that you will need to check too:
1. Is your property a house?
Flats, maisonettes or any other type of buildings do not have permitted development rights, so you won’t be able to build your extension without getting full planning permission. Also, be aware that if your property has undergone a change of use or has been converted into a house in the past, it may not enjoy permitted development rights.
2. Is your house, or any buildings contained within the boundary, listed?
If so, you will need to contact your local council as other permissions may be required e.g. listed building consent. This often requires more detail than a typical planning application.
3. Is your house in a conservation area or other ‘designated land’
This includes National Parks, areas of Outstanding Natural Beauty, the Norfolk or Suffolk Broads and World Heritage Sites. If so, you will not be able to build your two storey extension without full planning permission.
Note: The above advice relates to England, and policy in Wales may be different.
Get professional advice
The above is mentioned as an introductory guide only. Please always consult your local planning authority before starting work on your project. Your architect can do this on your behalf if you wish.
Choosing the right architect for your design project is a critical first step, but can also be a bit of a minefield. This is exactly why I set up this website in the first place!
As well as being founder of designforme.com, I am also a qualified architect. I found that many homeowners search online to find an architect and discover well established or high-end practices (it makes sense – these companies have bigger marketing budgets with stylish websites). However, such practices are often too busy, too expensive and, in fact, often less experienced in dealing with small residential projects on ‘normal’ budgets.
So, I wanted to create this platform for those design professionals I know who are suitable, experienced and eager to take on domestic projects like yours. They include small, young practices or freelancers. The problem was that, before Design for Me, they were very difficult to find! All you need to do is tell us a bit about your project…
Emily Design for Me