Multi Storey Extension Cost

How Much Does a Multi Storey Extension Cost?

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.

So, what's the cost of a house extension?

A small 30m² 2 storey extension costs £47,000 for average specs, but a larger 60m² 2 storey extension costs around £70,000 to build, and takes about 11 weeks.

If you want a larger 3 storey house extension, you'll be looking at costs closer to £165,000, taking up to 20 weeks to construct.

In comparison, single storey extensions cost in the region of £35,000 and take around 12 weeks to build.

What is your main reason for adding a multi storey extension?

Create additional living space

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To improve overall layout of property

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Multi Storey Extension Prices

The price depends largely on the size of the extension, with more storeys and a larger floor area naturally costing more than smaller builds. The average 3 storey exension cost will be much higher than a 2 storey extension occupying the same area.

Multi Storey Extension Costs per m²

A useful way to calculate the cost of your project is to consider the area of the extension. The typical double storey extension cost per m² is £1,566 for mid-range, average specs.

You can cut costs by choosing more affordable materials, but premium options will increase the value of your extension if you're looking to sell your property in the future.

Additional Costs of a Multi Storey Extension

Building a three storey extension is an expensive undertaking, and there are several additional costs to consider beyond the initial construction expenses:

• Planning permission fees — Depending on the size of your extension, planning permission may be required. This currently costs £548 in England.
• Architectural and design fees — If you need to hire an architect to draw plans for your extension, it will cost around £4,500.
• Structural engineer fees — The cost of hiring a structural engineer to handle the structural design of your extension can be up to £2,000.
• Building regulations approval fees — For a house extension, these can be up to £1,000.
• Utility connection fees (water, electricity, gas) — These can vary depending on your location and the specific utilities you need to connect, but expect costs in the range of £500 to £3,000.
• Interior finishing costs (flooring, painting, fixtures) — These costs vary significantly depending on the size of the extension and the type of finish you choose. Tiling a floor costs around £500 to £600 in a 12m² room, while painting a room costs roughly £250 to £400 for a small bedroom.
• Landscaping and exterior work costs — It's likely that some landscaping will be needed around the area the extension is built on. Average landscaping costs are around £505, depending on the extent of the work required.

Some of these costs may be included in the initial construction quote, while others may need to be budgeted for separately. It's always a good idea to thoroughly check what's included so you can plan your budget in advance.

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Cost Factors for Multi Storey Extensions

There are several things that can affect the overall cost of building a multi storey extension, including:

• Size of the extension — A 3 storey extension will cost more than a 2 storey extension as more materials, labour, and structural work are required. However, the groundwork and foundation work requirements are largely similar, so costs don't scale linearly.
• Complexity of the design — Simple layouts will be less expensive to build than complex, custom designs.
• Materials used — Higher quality materials and finishings will increase the overall cost of the extension.
• Area of the UK — Labour costs can vary significantly depending on the region and the complexity of the work.
• Location and accessibility of the site — Sites that are difficult to access or have limited space may incur additional costs as additional work or equipment may be required to bring materials to the site.
• Additional features — Any extra features or custom designs will increase the overall cost. For example, building a kitchen extension costs around £50,000, while a bathroom extension costs around £1,300 per m².

Multi Storey Extension Rules and Regulations

Planning Permission for Multi Storey Extensions

Planning issues are common with multi storey extensions.

Most local authorities insist that extensions are smaller than the original main building. This means the roof must be lower than the original property's roof, and the first-floor walls need to be set back from the front of the existing building. Planners generally don't want the extended house to look significantly larger than all the other houses on the street.

When a two or three-storey extension is proposed, it will naturally get more scrutiny than a modest single storey extension because it will have a more visible impact on the house’s appearance with a higher possibility that it will also impact the neighbour's privacy or sunlight.

• Projection — Under permitted development, two storey rear extensions must not extend beyond the original rear wall of your property by more than 3 metres.
• Boundary Proximity — They also must be 7 metres from the boundary opposite the rear wall.
• Roof Pitch — The roof pitch of the extension should match the original property "as far as practicable".
• Windows — Side elevation upper-floor windows need to have obscured glazing.
• Planning Permission — Side extensions of more than one storey need planning permission.

Permitted development (PD) rights for multi storey extensions are very limited:

• Terraced Houses — A two-storey extension on the front is unlikely to get permission but a rear addition may be acceptable and the projection of the upper storey will be limited as the neighbours are so close.
• Three Storeys — If there are no three storey houses on your street this will be a major challenge to get planning approval.
• Neighbour Privacy — You must ensure that the privacy of your neighbours' back gardens is not compromised and that the new extension is still subsidiary to the original house.
• Planning Fee — In the UK the cost to apply for planning permission for a house extension is £258.

Building Regulations for Double Storey Extensions

Before you start any construction you need to make sure your home extension plans comply with Building Regulations. Building Regulations set the minimum building standards.

At times during construction a building inspector will visit the site to ensure that all building regulations are being met. Once the extension is finished the council will issue you with a Completion Certificate.

• Escape Windows — In multi storey extensions each habitable room should have an escape window where required, or a protected escape route can be used instead.
• Protected Escape Route — A protected route from higher floor bedrooms to the outside is required with walls that can resist fire for 30 minutes.
• Structure — If the second floor is completed with full-height walls the extra weight on the lower walls may mean that denser stronger blocks will be needed on the ground floor.
• Insulation — Denser blocks are not as good at insulating as lightweight blocks so extra insulation may be fitted in the form of dry lining.
• Inspections And Sign-off — Expect periodic inspections during the build and a Completion Certificate at the end.

Checklist: Hiring a Builder for a Multi Storey Extension

Well-designed house extensions can transform homes by maximising the usable floor space, while adding to the market value. Here's what you need to know when hiring a local builder for your project:

• Have you checked multiple quotes? — Using MyJobQuote, gather at least 3 quotes from builders near you to compare their extension costs.
• Are there any additional costs? — Get a full cost breakdown and check to see if waste removal, skip hire, scaffolding hire, and other additional costs are included, or if you need to arrange for these separately.
• Are they qualified? — Look at their qualifications. Multi storey extensions are skilled projects, so the builder should have ample experience in building them.
• Are they part of the FMB? — See if the builder is part of the Federation of Master Builders (FMB).
• Do they have positive reviews? — Read their customer reviews, taking note of any comments on timekeeping, professionalism, and quality of work.
• Do they have examples of similar work? — Look at photos or videos of their previous projects to get an idea of their style and finish, and make sure this matches your expectations.
• Do they have insurance? — Make sure the builder is insured with public liability insurance and employer's liability cover.
• Do they offer any guarantees? — Remember to ask about any guarantees or warranties on the parts and labour.

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