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The cost of building an extension in 2017

building extension

The cost of building an extension varies depending on what the extension is, the size and difficulty of the addition are a huge factor in the price. When trying to access the cost of your addition, you will need to be aware of how many general contractors, electricians, plumbers, carpenters or decorators you will be needing. Another thing to consider is the price of the permits and inspections.

Planning the Extension

Before you begin the process of adding your extension, you will want to consult an interior decorator. However, you should be aware of decorators who say they offer free services these could be a representative for a manufacturing company who are trying to sell you products you do not want or need.

Make sure that after you have chosen your decorator to compare prices they give and the actual retail price. Another thing to think about when deciding to add an extension is the possibility you may need to hire a structural engineer; structural engineers inspect the foundation, infrastructure, curtain wall, and insulation.

Budgeting for the Extension

When you are planning an extension before hiring contractors or decorators, you need to plan your budget. The great thing is you can change any plans you may have to fit into your budget. You can choose a lower-grade carpet as opposed to a higher-grade. The best place to ask for a quote is Paradisehome.

Waiting for sales is a great way to save money on paint, appliances, flooring, and windows. Begin buying items you will be needing ahead of time and do not be ashamed to use coupons. If you purchase items over time you may be able to afford an item you would not afford if you buy everything at once.

Different Types of Extensions

If you are planning a single storey extension first, you need to think of the size; we’ll go over the cost for a 4M x 5M single storey addition. As a general rule of thumb, the cost in London is £1,500 – 2,000 per m2, this means that if you are building a 4 x 5m extension the cost to build would roughly be £24,000. However, this price is before adding on 10-15% for the professional fees that will be incurred adding these charges and the VAT.

The price of your single storey addition will cost you £32,000

A Double Storey Extension

For the double storey extension, we will continue to use the 4M x 5M size. Since the size is the same as a single storey addition what you will need to do to figure your price is to add 50% to the build cost of the single storey we just went over. This means that the £24,000 + 50% = £36,000. You will need to add 10 – 15% of your professional costs, this plus adding the VAT will bring your cost for a second storey addition to £48,000

different types of building extensions

Take into account that the above figures reflect a standard extension with no complications. You will find these values in most parts of the UK. However, these numbers could get higher if the following apply:

When a kitchen or bathroom need adding, then you need to consider the cost of the plumbing involved. An ideal amount to add a kitchen is£10,000. This amount, of course, will depend on your specifications, but with the£10,000you should be able to build a lower-mid range kitchen with appliances.

The cost of adding a bathroom will be about half the cost of building the kitchen, which would be £5,000.However, as with the kitchen addition, the amount will depend on your specifications.

Finishes and Fittings

When adding a kitchen or bathroom, you need to consider the cost of the finishes and fittings. The total amounts of the kitchen and bathroom extensions above are for modest finishes, accessories, electrical and lighting. If you want higher-end finishes, your cost will go up. Some examples of higher-end finishes are; tile finishes and fitted joinery.If you want to keep your cost down then choosing the lower-mid range finishes and fittings will help.

Any Site Constraints

One of the things that you should look at when planning an extension is are there any site constraints, if so then your contractor/builder will need to include the additional costs in their quote. A few of the restrictions that could cause the additional costs are as follows:

  • The soil and ground conditions could cause more costly methods
  • Limited access to the site. The contractor should be able to bring his tools and machinery in and out quickly
  • Are you removing any structural walls? If so additional costs for steelwork will apply
  • Will there be any pipework, drainage, and gas meters that need to be moved?

Managing and Reducing Extension Cost


reducing extension costs


  1. Get professional advice from a good architect. They are there to help you realize your primary goals for the expansion. They can also assist you in controlling your costs by working closely with you so that you are able to get the most out of whatever budget you have.
  2. Get 3 – 5 quotes from your contractor/builder. Getting these quotes will help you get an idea of what your costs could be before starting the work. Ask your architect for a list of the best contractors/builders in the area. Your architect can also help in creating your contract.


What is Vat?

If you are new to home extensions and are unsure of what the VAT is we have included an explanation so that you are acutely aware before starting your extension. The VAT is a value-added tax that is placed on a product whenever value, is added at a stage of production and final sale.


It is true that an extension can be an overwhelming project to take on, but as long as you know what your plans are, what your budget is, and you find a great architect and designer to help during the process then the stress will be a lot less. Also having your plan and budget ready will assist in knowing what you can and can’t do.