How much does a home extension cost?

Planning Your Home Extension

Extending your home can be a great way to gain more livable space. It can also be a way to add value to your home.  
 

But, extensions don’t come cheap. So, how much can you expect to spend? 

Step 1: Planning 

Sue and Kevin are a married couple living in Cardiff with 2 children who are now at university. They enjoy entertaining and throwing parties with their large family. They are looking to gain more usable space in their home and want to extend the downstairs to add a toilet and a larger kitchen.

 

It is important to come up with a financial plan. Where is the money for your extension coming from? Are you going to remortgage your home? Will you get a loan from the bank? Do you have savings you want to use? Or will you use a combination? 
 

Once you have decided how much you can afford to spend you can start looking at what you want. 
 

The cost of your extension will depend on the type and the quality of materials. But variables like location, and size, will make a difference. A single-storey extension could cost you anywhere between £1500 and £3000 per m². In some cases, it could cost more. 
 

You also want to consider additional costs like plumbing, electrics and pipes. For example, if you are thinking of a kitchen extension you may need to have the pipes reworked for a gas cooker, or if you are fitting a new bathroom, you may need a plumber for all the pipe work and an electrician for the light fittings. This will add more to the cost.

Step 2: Decide what you want  

After measuring the area they want their extension to be, Sue and Kevin estimated that their extension will cost £60,000 total. This includes building, plumbing, electrics and final fixings. They have decided to remortgage their home and use their savings as a safety cushion if needed.

 

The type of extension you choose will depend on the type of property you own and what you are looking to gain from it. The type of extension you choose will also impact the cost, so you may want to consider your budget as well.  
 

Some of the most common ways to extend your home are: 

• single-storey extensions  
• multi-storey extensions  
• side extension 
• kitchen extension  
• loft conversion  

Step 3: Get expert advice 

Sue and Kevin know with their £60,000 budget they can only afford a single storey extension. They are happy with this as they just want a downstairs toilet and larger kitchen. This will allow them to get the space they need without making their house feel too small. In total they are looking to extend by 20m2.
 

The type of expert you want to speak to first may depend on what you want out of your extension. 

 

Architect and structural engineer 

You may want to speak to an architect and structural engineer before making home improvements. They can help you plan your project and help ensure that the extension complies with architectural and structural building regulations.  
 

The design should outline the project clearly and see how your extension will look and function. You can use this to get a fixed quote from your builder.  
 

Architect fees can cost up to 10% of the construction cost. Structural engineers generally cost around £400 for a basic domestic project. 
 

It's not required by law to hire an architect or a structural engineer. It is recommended to hire a structural engineer for projects where structural changes are being made to your home.  

 

A builder 

Builders can usually answer any questions you have, show you what they can do and what is possible for your home.  
 

It is always a good idea to get several different quotes, look at past work and previous clients before making a decision on who you would like to work with. 
 

Sometimes, quotes from builders can be over budget. If you have a strict budget, you may want to consider ways to bring down the cost.  
 

• Are you able to carry out parts of the build yourself?
• Could you use alternative materials like having radiators instead of underfloor heating?
• You could also reduce the scope of your project and tweak your original design plan?
• Reducing the size of your extension will bring down the cost. 

Planning permission 

You may want to check with your Local Planning Authority (LPA) to find out if your extension needs planning permission. You can apply online. Costs are usually around £462.  
 

If your plans are rejected, you may need to consider changing them to fit within your allowed limit. 

Step 4: Budget!  

Sue and Kevin decide that they would like to speak to an architect to draw up plans of what the extension can look like. This costs them £3000. They then speak to 3 builders and show them these plans. After looking at the work one builder completed on their neighbour's property they decide to go with Jones Construction. They are quoted £43,000 and receive all the relevant documentation from the construction company before work begins.

 

In step 1 you set out a rough budget, you then work with various trades to come up with a quote for all works. Once everything is agreed you then need to manage your building project and budget.  
 

The total cost of your extension can vary greatly depending on the work you have done and the quality of materials. 

 

What should you budget for:  

• insurance: it is important to tell your insurance company that you have planned building work before it starts. Your premium will likely increase. But this will ensure you’re covered during the build and that your extension is included once complete. 
• decorating & finishes: once an extension is built, they need final touches like paint, flooring, doors and windows. Consider what you will need and factor this into your budget. 
• temporary accommodation: depending on the extension, you may not be able to live in your home during stages of the build. You will need to consider somewhere safe to stay during these stages. To save money, consider asking family or friends to stay with them. 

Which? recommends that you should set aside an extra 10% for unexpected additional costs.