How much will my project cost?

Written By Jamie Nicholson

At this stage, you should have a really good idea of what you want to achieve by undertaking your building project. If not, head over to our post on creating your design brief before reading on below.

Knowing your ‘why’ will be invaluable when it comes to deciding how much you want to invest in the work.

Why Is Setting a Budget So Important

Setting a budget can get lost in the excitement of designing a new space, but it’s a crucial exercise if you want to start your project out on the right track. Having a budget in place has been shown to significantly reduce overspend compared to a carte blanche approach and this, in turn, will reduce the financial stress you encounter during the work.

By establishing a clear budget from the outset, you can also realistically assess what you can afford to spend and allocate your resources accordingly. Being able to plan and monitor this throughout means you can prioritise what aspects are most important to you, whether it's the quality of materials, the size of the space or how well it should perform when finished.

You can also use your budget to convey this thinking to your design team - ensuring you’re all on the same page and working toward the same goal.

Key Factors Influencing Extension Costs

Size

The size of the extension is a significant factor in determining the overall cost. As you can imagine, larger extensions require more materials and labour, leading to higher costs.

Design and Complexity

The complexity of the design and the features you include (such as skylights, bi-fold doors, quality of materials) can all impact the overall cost.

Location

The location of the property and its impact should be accounted for from the outset. Construction rates can vary depending on your region due to differences in material and labour costs. For example, it’s typically more expensive to build in London and the south.

Difficult Site Access or Soil Conditions

Difficult site conditions might require costly solutions to overcome. This can be in relation to the foundations/footings or, more generally, to accessing and using the site.

Building Performance

New homes and retrofit projects are designed to reduce energy usage and bills, which can usually attract a 10-15% uplift in the initial cost of the work. Savings may be made longer term, so refer to your brief to decide if this is the right route for you.

Extent of Structural Changes

Depending on how much will change as part of the work, complex structural alterations can also require more expensive solutions.

Statutory Approvals

Being in an area with a natural or conservation area designation might mean that the planning process is more onerous and will likely increase the cost of your design teams input.

Home Insurance

You should inform your insurer if you plan to do any work and arrange appropriate cover of the construction and the new building or additions.

Approximate £ / sqm rates. Feb. 2024

Before looking at any cost per square metre rates (£/sqm), it’s important to acknowledge their limitations and identify their exclusions.

Whilst they can be helpful to get you a ball park figure, a more detailed break down is absolutely essential for proper budget planning.

The figures below show a (very general, high level) indication of what some types of work and the level of finish can cost based on size. They exclude VAT and the internal fit out, so be aware that you may only be paying for the outer shell on this type of quote.

Single Storey Extension

  • Average - £1500 to £1750 / sqm

  • Good - £1700 to £2100 / sqm

  • Excellent - £1800 to £2500 / sqm

Double Storey Extension (slightly cheaper £/sqm)

  • Average - £1500 to £1700 / sqm

  • Good - £1650 to £2050 / sqm

  • Excellent - £1750 to £2450 / sqm

Retrofit

  • Light retrofit - £800 to £1200 / sqm

  • Deep retrofit - £1000 to £1500 / sqm

New Build Home

  • Anywhere between £1000 and £3000 / sqm (which is incredibly vague because of the number of variables)

In addition to calculating the ballpark figure based on the area, you can also expect to pay 30-40% of that figure again to fit the space out. With this in mind, it’s easy to see why this is finger in the wind territory and how having drawings which can be properly costed can be really beneficial.

What Professional Fees Should I Include in My Budget?

Which professionals you might need on your design team will vary from project to project, although the list below illustrates some of the construction professions, and their associated fees, that you might encounter during the work. Click here to read my article on how to pick the right team for you. These figures are extension/retrofit only as there are too many variables on a new build home to list.

  • Architect / Designer - between 5-15% of the construction value, depending on their level of involvement

  • Building Surveyor - approx. £500 to £1500

  • Structural Engineer - approx. £500 to £1000

  • Contractor - materials + labour + profit, beware VAT @ 20%

  • Planning Submission (if required) - householder £258 (+£64 service charge)

  • Building Control - approx. £492 to £752 (inc. VAT)

Conclusion

Building or renovating can be a worthwhile investment that can drastically improve your life and increase the value of your existing home/site. The broad spectrum of costs above should demonstrate the need for a detailed cost breakdown and the benefit of getting multiple quotes for your project.

If you’re unsure where to get started with your brief, a budget or you want some input on your designs get in touch on the details below and we’ll arrange a chat.

Jamie Nicholson