What is The Cost of An Extension?

As interest rates go up, an increasing number of homeowners prefer extensions instead of upsizing to have the necessary space. Actually, the number of people who think that extending their home is a better option than relocating doubles the number of people who think in the opposite way.

When you take legal costs, Mortgage adjustments, Stamp Duty and inevitable costs of relocating and increasing prices of homes, it would be a better option to expand your home instead of moving into a new house.

Coin in jar

The prices of an extension would be really affordable as compared to relocating, however the costs could still be high for most people especially at first blush. Like all services and goods, the prices of extension also hinges on your wishes.

The most important factors which affect the total expenses are place, size of the area and the kind of extension. For instance, the cost of one story extension in a smaller city, would not be the same as a two storey extension in London or another big city.

In this article, we’ll show you different factors which could affect the price of an extension. After reading this article, you may have an idea about the total cost of the extension that you need to pay.

Which Type of Extension Is The Right Choice For You ?


Single Storey - The extensions which are called as Single story extensions takes the form of rear or side extensions. If you want to extend the first floor of your home, £1,200 to £1,500 payment per square metre would be a realistic estimate for you. In London and its suburbs, the average price of the extension could rise up to £1,400 to £1,900+ per square metre. So, we can say that, a typical extension of 4 metres by 5 metres would cost around £27,000 in most cities of the UK, or £35,000+ in London. When you take professional costs and VAT into account, the total expense of a single storey extension would be around £35,000 in the most UK cities, or £45,000+ in London.

Two Storey Architecture

Two Storey - The usual final cost of a two storey extension would be around £55,000 or £70,000. Your nearness to London would affect the final price. It is possible to say that, two storey extensions costs less per square metre when compared to single storey extensions because the expenses of substances which are used for structural support just as the foundations and the roof is mutual in two storeys. On the other hand, obtaining a planning permission could be harder than single storeys because of larger size and complexity of two storey. In addition to this, the expenditures of experts just as engineers and architects would be higher in general.

Basement – Basements are generally more costly than single or two storey extensions. (It is very trendy in wealthy areas in London recently). What makes the basement more expensive than single and two storey is the groundwork. Extending or converting a basement is a complex work. Thus, starting prices for this work are about £2,500-£3,000 per square metre generally in a standard UK city, and between £4,000 and £5,000 per square metre in the London area.

What is the Role of the extension?


The second most important factor which affects the cost of extension would be its role. In other words, how you are going to use it. Two of the most popular roles of extensions in home are;

Bathrooms – Embodying an intermediate level bathroom to your extension will add up £5,000 to the final price. This price includes usual stuff such as toilet, basin, bath. However, we need to state that the costs will mainly be affected by the finishings and fittings.

Kitchens – This is generally a more complex work when compared to bathrooms. Therefore, the additional expense of a kitchen operation will be about £10,000 at least. This price is based on an intermediate level kitchen. The final price of a kitchen operation would depend on the goal you want to achieve.

To obtain a planning permission for bathroom and kitchen, building plans should include electricity, plumbing, and gas delivery system for kitchens. Although including all of them would be expensive, we advise you to include them because the possibility of your application being granted would increase.

Moreover, a professional installation secures the effectiveness of the extension and safeness of your home. You should now that, this is priceless !

Main Expenses to Consider !


Architect – Architects are the people who make your extension idea come true. The comprehensive plans of architects guarantees exact quotes from builders, and thanks to their wide knowledge about features of the work and local authorities pave the way for the planning application procedure.

The expenses of architects differ from companies to companies, so it would be better to get a price quote from different companies. As Studio20 Architects, our starting prices for the planning package is about £300 per floor. We offer hoe design and supervision of your planning application to you.

Planning Planning is one of the stable expenses while installing an extension to your home. The price of a standard planning is exactly £206. However, keep in mind that, perhaps you would not need a planning permission for your extension if it ranks as your permitted development rights. In this kind of situation, your extension would be required to be documented with a lawful development certificate.

The average prices of these certificates are around £103 . Even though getting these certificates are not necessary, it would help you against potential problems which you could face in the future, especially which you could experience while selling the house. You can find more information about different kinds of planning fees which could fit your extension on the planning fees guidance page of the planning fees guidance of Gov.uk website


Construction – As you can see above, the main cost of installing an extension to your home is the cost of construction. All building stuff and work expenses are included in construction costs. On average, the construction costs form 50-60% of total extension costs. This percentage could rise up to 80% when the VAT is included.

Other professional expenses If your extension plans on your home are very detailed, you would need to employ extra professionals in the process. You may consult your architect to learn which professionals you need.

For instance, assistance of a structural engineer would be helpful to measure the foundation of a home in many extension projects. This service would add about £500 to £1,000 on average to the final price. As Studio20 Architects, we offer you the best service from the most respectable experts in the area you live in to carry your project one step further.

Insurance Insurance is perhaps the most ignored part of an extension plan. We always advise our customers to get in touch with their insurance company about their project. Your house may not be covered by your insurance policy during the construction. Therefore, we advise you to get contact with your insurance company to learn the details.

If your home is not covered by your insurance company during the work, you would need to take out an extra policy during construction. Of course the extra insurance for the extension will increase the expenses. However it would not be too expensive, and you will feel at ease during the construction.

VAT – Tax is one of the expensive costs everytime and it is the same for the construction process. However, you have to pay it. Almost all kinds of extensions are liable to full rate of VAT and it is at 20% today. On the other hand, do not think that there is nothing you can do to lower the rate of tax.

For example; installments which enhance the energy efficiency of elderly people's properties, turning a nonresidential structure into a house. This application is common in residential possessions which has been empty for more than two years. Based on the accurate details of the work, VAT may be decreased to %5 at most.


Eyeball Estimate

As you probably know, there could be several factors which affect the total price of an extension.

However, the detailed account below, may provide an insight to you about all expenses which you will face during the extension construction.

Architects - 2% Administration fees - 1% Structural Engineers - 2% Surveyors - 1% Contractors - 33% Materials - 20% Fittings - 5% Glazing - 15% VAT – 20%

General Suggestions

It could be a difficult task to budget an extension, especially nowadays while prices could rise rapidly. On the other hand, estimating possible costs, and being prepared is still the best thing you can do to secure your extension project. In this, the project could run properly.

We advise you to have an idea about the potential cost of extension, and how much time it takes to construct it. You can budget the project better, and could be prepared against contingencies. If you follow our suggestions, unexpected situations and potentially expensive problems would not upset you.

If you still have unanswered questions in your mind, you can enroll on a free consultation call with our team who are experts on extension fees, planning permission, or another issue about the extension process.

Similarly, if you think about having an extension on your property or want to have an information about extension potential of a new home, you can receive an instant price quote today.