The Cost of a Double Storey Extension

All you need to know about having a double storey extension built including the costs of materials, labour and time frames.

The Cost Of a Double Storey Extension

What the job entails

Over time homes can become a tight squeeze as children grow in size and number! Rooms can quickly start to feel smaller than they used to and before long many start to question whether they should move somewhere bigger, or build an extension. Sometimes the decision is pretty straightforward, after all, if you live in a flat with no garden, there is little point considering an extension! But if you have a house with outside space, extending your property is a possibility. Whether an extension is the best idea really depends on your location and the financial implications of moving home versus extending.

If you live in a city or other highly desirable area where real estate is sought after, then the reality is that extending is usually the sensible thing to do, at least from a purely financial point of view. But the extension does need to be well planned and professionally constructed, nobody really wants a bigger house with no parking or garden area, so you need to consider the resale value and desirability of the finished project.

A double storey extension is a major job so expect lots of upheavals! There will need to be extensive foundation work to support the extension, so lots of mess and much removal. Many trades will be required such as bricklayers, joiners and electricians, plus scaffolding will need to be erected. The job will probably take months rather than weeks and if you cannot move out while works are in a progress, you will certainly wish you had after a few weeks!

The basic outline for the work will be first of plans being drawn up and approved, then foundations dug out and concrete pouted, then the alls/frame will be built, followed by the roofing then windows and a door to make the extension waterproof. Now the interior work such as electrics and any plumbing can be carried out, with flooring and decorating to finish off.

Often when building an extension other related works are required. Typically there will be a need for some hard landscape work as the new build will extend into the garden space with a new door therefore a new path or patio area will often need to be formed. If the new extension is going to swallow up the existing garage or parking area, then some thought will also have to be given to alternative parking arrangements which may include laying a new driveway.

A two-storey extension is a major job and will be very expensive, if the property is not in a highly sought after postcode then the investment may not be fully recouped when it is sold. The cost of a double storey extension needs to be considered carefully against the cost of simply moving to a bigger house. Even in desirable areas, postcodes in those areas will often have a price ceiling which will limit the potential for added value to any property.

Problems with extensions almost always occur due to the homeowners not getting professional advice (or not following it) or, trying to save money by going the DIY route or using cowboy builders. If professionals such as architects are consulted and plans are drawn up properly, then reputable builders are hired, the chances of things going badly wrong are greatly reduced. In the unlikely event something does go wrong, then at least reputable architects and building companies will be fully insured and at least will have an actual address where you can serve court papers if necessary!

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The Cost of a Double Storey Extension

The figures provided should give a rough idea of the costs involved if you are considering a double storey extension, but of course you will need to gather detailed quotes from tradespeople to get an exact price for your requirements.

The average material cost for a double storey extension will depend on factors, such as size, materials and finish. Having a double storey extension will increase the size of your property dramatically, adding several new rooms, so you also need to consider the materials and labour costs involved in the finishing, decorating and furnishing of each room.

The average builder will usually charge around £1200-£1800 per m2 for a double storey extension, usually anywhere from £150-£250 per day per builder depending on their skill level. So a master builder would charge a daily rate near the higher end whilst a general labourer or apprentice would be at the lower end.

For a double storey extension you will need a few different trades to complete your job. An architect and a structural engineer are going to be needed to help with the planning applications, reports and to follow relevant building regulations. A builder and roofer to complete all of the structural work. An electrician to install the cabling and lights. A heating engineer or plumber to install your water mains to allow for sinks, showers, toilets and radiators. And of course the finishing trades such as plasterers, tilers, decorators and flooring specialists.

The scale of your extension also depends on the rooms you will be adding so you need to consider how you want to design your home around your additional space. With the amount of trades needed you should expect your extension to take several weeks at a minimum.

Below are some estimated costs of a double storey extension:

Job Description Avg. Cost Duration
Double storey extension totalling 30 m2 £40,000 - £55,000 8-10 weeks
Double storey extension totalling 60 m2 £65,000 - £75,000 10-12 weeks
Double storey extension totalling 100 m2 £90,000 - £100,000 12-14 weeks

Cost Breakdown

Individual costs of a double storey extension totalling 60 m2 - Total Cost: £70,000






Waste Removal


You really need to weigh up the pros and cons of both options carefully, if you are planning on starting a family or a home business and need extra space, then research the costs of moving house and check property prices in your area then contact local builders for quotes to compare costs. If you have the garden space and you live in a desirable area, an extension could well be the better option.
The permitted development rights do allow for two-storey extensions in certain circumstances. But the extension must not extend beyond 3 metres and must be a minimum of 7 metres away from the land boundary. The eaves of the extension also cannot exceed 3 metres in height. In all cases, you should discuss your plans with the local authority and consult an architect or other professional before starting any building work.
If you share a boundary wall with any neighbours you will need to get them to consent formally to the extension, otherwise, you will need a Party Wall settlement. Failing to observe the party wall act could mean your neighbours can take civil action against you and stop the extension, which will delay the project and increase costs. They can also get compensation and potentially force you to make good any work already carried out!
On average a double storey home extension will take around 3 months to complete, although this will, of course, depend greatly on the size and specification of the extension and the company doing the work.
For a set of plans to be approved through the planning permission process, it will take around 8 weeks.
A lot! Building work can often be disruptive and stressful, so if budget allows, avoid the disruption by moving out until the construction phase is completed and remember to pack away any valuables or anything that could get damaged. If you cannot move out, a professional building company will take steps to minimise disruption, but they cannot work miracles.