Multi Storey Extension Cost
Guide to multi-storey house extensions with typical costs
For many families there comes a time when the home becomes a bit of a squeeze, so should they move to a bigger house, or extend the home to make it large enough for all the family and their activities? Sometimes the choice is determined by the situation, for those that live in flats with no gardens, for instance, extending is simply not possible in most cases. But for those that have space to the front, side or rear, extending is a possibility worth considering, especially in cities where space is at a premium. Whether it makes more financial sense to move to a bigger house or to extend, depends on a number of factors, but in most cases extending makes more sense financially, so is the better option, particularly if you like the area. Extending can consist of adding a single room such as a conservatory, or extending the existing living space across two or more storeys with a full extension offering multiple additional rooms and lots of extra living space. A multi-storey extension is beyond even the most dedicated DIY enthusiast and will require multiple trades to build. So you need to either hire architects, electricians, gas fitters, plumbers and builders separately - or hire a specialist building company that has all the necessary expertise in-house, or at least has special relationships with all the necessary tradesmen so they can manage the entire project on your behalf.
Average costs for building a multi storey extension
Things to consider regarding multi-storey extensions
Planning issues are common with multi-storey extensions as most local authorities insist that the extension is subsidiary to the main building with lower ridgeline must be lower and the new first floor walls stepped back from the existing ones at the front. Effectively, the planners do not want the extended house to look significantly larger than all the other houses in the street to avoid setting unwelcome precedents. So if you were thinking about doubling the size of your existing home then you will probably need to think again! When a two or three-storey extension is proposed, it will naturally get more scrutiny than a modest single storey extension, as it will have a more visible impact the house’s appearance with a higher possibility that it will also impact the neighbour’s privacy or sunlight. The permitted development (PD) rights for multi-storey extensions are very limited indeed.
A terraced house is unlikely to get permission for a two-storey extension on the front at all, but a rear addition may be acceptable. However, the projection of the upper storey will also be limited as the neighbours are so close. A common 2 storey extension project is a ground floor extension to a rear kitchen, with a new bathroom in the smaller extension above. Another point to consider with terraced properties is that you will be unlikely to add the full cost of the construction onto the new value of the house. With a typical three-bed semi, there is also scope for a multi-storey extension between the side of the house and the property boundary.
If you want to add a three-storey extension and there are no three storey houses on your street, this will be a major challenge to get planning approval. To get permission you will have to ensure that the privacy of your neighbours back gardens is not compromised and the that the new extension is still subsidiary to the original house. Remember also that in multi-storey extensions the building regulations insist that at least one window to any room has to be an escape route in case of a fire. The top storey windows have a greater risk of injury so a protected escape route that runs from the higher floor bedrooms to the outside is required with walls that can resist fire for 30 minutes.
If the second floor is completed with full height walls, as opposed to making use of ‘room in the roof’, the extra weight on the lower walls may mean that denser, stronger blocks will be needed on the ground floor. These are not as good at insulating as lightweight block, so extra insulation will have to be fitted in the form of dry lining.
Doing it Yourself
Going the DIY route on an extension will more than halve your costs, so this initially seems like a very attractive option! However, you will have to come up with a plan and design that is suitable for the planning department, then carry out the build meeting all building regulations passing periodic inspections from the local authority, plus any electrics will need to be checked by competent electrician and signed off and all gas-fittings must be done by an approved gas fitter. So there are parts of the job that can be done on a DIY basis, but you cannot tackle the entire job without professional help.
Some parts of the job can be taken on by the DIY enthusiast to save money, for example, you could perhaps dig the foundations and pour the concrete, plus much of the interior fittings and finishings are unskilled work. But plan on realistically hiring a plumber, electrician, gas fitter, builder and architect.
Multistorey extension checklist
- Well-designed house extensions can transform homes by maximizing the useful floor space while adding to the market value
- Before you decide to extend, consider converting existing space such as doing a loft or cellar conversion
- To achieve a seamless extension you need to match materials and put old and new together
- Small gardens will suffer if reduced even further by a house extension
Hiring a Tradesman Checklist
- Always get at least 2 quotes before hiring.
- Never pay the full amount upfront.
- Get the quote in writing.
- For any payment you make, always get a receipt.
- On more expensive jobs, ask for references.
- Check if the tradesman is a member of any trades associations.
- Make sure the tradesman has public liability insurance.
What are the Building Regulations for multi-storey extensions?
What is the Party Wall Act?
Do I need an Architect or Chartered Building Surveyor?
What is permitted development?
How long will it to get planning permission?
Ground floor kitchen shower extension.
Submitted by Sam
Hi there, planning to build a new bedroom top of the garage.
Submitted by Wasim
Single story kitchen diner rear extension, the same width of the house. Currently, 1 small extension/sunroom that is not keyed into the house which needs knocking out which will be replaced by this extension and remove the wall from kitchen to sunroom. Wanting to be done asap and completed within a ...
Submitted by Daisy
We have had an L-shaped extension done onto our house. It has been roofed and glazed. The builder did not finish the walls up to roof height, and left the job as he was offered a contract in London, and said his mate would come around and finish the job. His mate came around and fitted barge-boards ...
Submitted by Rick
Conversion of a conservatory to a dining room with a bit more extension to sideways. Building plan in hand.