5 Budget & Planning Mistakes Homeowners Make When Building an Extension

Building an extension is an exciting way to create more space, improve how your home works and potentially add value to your property. But before the first brick is laid, there are several important decisions that can have a major impact on the cost, timescale and overall success of your project.

Many extension problems don't start during construction — they start during the planning and budgeting stage.

Here are five common budget and planning mistakes homeowners should avoid when considering an extension.

1. Not Allowing a Contingency Fund

2. Rushing the Design

3. Making Changes Once Construction Has Started

4. Ignoring Planning, Building Regulations and Other Requirements

5. Looking Only at the Headline Price

1. Not Allowing a Contingency Fund

One of the biggest mistakes homeowners make is budgeting right down to the last pound.

Even with detailed plans and a carefully prepared quotation, unexpected issues can sometimes be discovered once work begins. This can be particularly relevant when extending older properties, where existing foundations, drainage, structural elements or services may not be exactly as expected. - Getting out of the ground can be the most expensive part of any build.

For this reason, it is sensible to consider allowing a contingency within your overall budget.

Many homeowners allow around 10–20%, depending on the age and condition of the property, the complexity of the project and how much uncertainty there is before work starts. A contingency isn't money that you necessarily expect to spend. It is there to give you some financial breathing room if something unexpected is uncovered.

It is much easier to deal with an unforeseen problem when you have already allowed for it in your budget.

Remember:

Your contingency should be in addition to your expected project cost, rather than money you are relying on to complete the planned works - like a rainy day fund for those unexpected things that crop up.

2. Rushing the Design

It can be tempting to get the building work started as quickly as possible, particularly when you're excited about creating your new space. However, rushing the design stage can create problems later.

Before construction begins, you should have a clear understanding of what you want the finished extension to achieve. This includes considering the layout, room dimensions, windows and doors, electrical points, lighting, plumbing, heating, ventilation, flooring and other fixtures and finishes.

Small decisions can have a surprisingly large impact once construction is underway.

For example, changing the position of a kitchen sink after plumbing has been installed, moving electrical points after walls have been plastered or changing the size of a window opening can result in additional work, costs, materials and delays.

Spending more time getting the design right at the beginning can help reduce the need for expensive changes later.

3. Making Changes Once Construction Has Started

Changes during construction can happen for many reasons. Sometimes homeowners change their minds, while in other cases they may realise that something doesn't work as expected once they can physically see the space taking shape.

However, even relatively small changes can have a knock-on effect.

A change to one part of the project can affect several different trades. Moving a doorway, for example, could affect brickwork, plastering, electrical work, flooring and decorating.

Changes can also disrupt the planned sequence of work. Trades are often scheduled around one another, so changing the programme can result in additional labour costs or delays.

This is why it is important to make as many decisions as possible before construction begins.

Of course, some changes are unavoidable. The important thing is to understand the potential cost and programme implications before agreeing to them.

4. Ignoring Planning, Building Regulations and Other Requirements

Planning an extension isn't just about deciding where you want the new room to go.

Depending on the property and proposed work, there may be planning requirements, Building Regulations requirements and other considerations that need to be addressed before or during construction.

Building Regulations cover areas such as structural safety, insulation, fire safety, drainage, ventilation and electrical and other building services.

There may also be considerations relating to neighbouring properties. For example, work that falls within the scope of the Party Wall etc. Act 1996 may require the appropriate notices or agreements with affected neighbours.

The exact requirements will depend on the property and the proposed work, so homeowners should establish what applies to their particular project before construction starts.

Trying to deal with regulatory requirements after work has already begun can cause unnecessary delays, additional costs and potentially the need to alter completed work.

5. Looking Only at the Headline Price

When getting extension quotes, it is natural to compare the final figures.

However, the cheapest quotation isn't necessarily the best value.

Two builders can provide very different prices for what appears to be the same extension because the quotations may not include exactly the same work.

For example, one quotation might include plastering, electrical work, plumbing, flooring and waste removal, while another may exclude some or all of these items.

Before comparing prices, make sure you understand exactly what is included.

Ask questions such as:

  • What work is included?

  • What materials and finishes are included?

  • Are electrical and plumbing works included?

  • Is plastering and decorating included?

  • Are flooring and final finishes included?

  • Are waste removal and skips included?

  • Are there any provisional sums or allowances?

  • What work is specifically excluded?

  • How will additional or unforeseen work be priced?

A detailed quotation may initially appear more expensive, but if it includes significantly more work, it could actually represent better value.

Planning Your Extension Properly Can Save Money

A successful extension isn't simply about finding the lowest price or getting the building work started quickly.

Good preparation can make a significant difference.

Taking the time to develop the design, understand the regulatory requirements, establish exactly what is included in the quotation and set a realistic overall budget can help reduce the risk of unexpected costs and delays.

It's also worth remembering that your extension is being built around your existing home. The condition of the property, existing drainage, foundations and services can all influence what is required.

The more that can be identified and considered before construction begins, the better prepared everyone will be.

Planning an Extension?

At DMS General Building & Maintenance, we understand that extending your home is a significant investment.

From initial discussions and planning through to construction, we believe clear communication, realistic budgeting and a well-defined scope of works are essential to a successful project.

If you're considering an extension and want to discuss your plans, get in touch with DMS General Building & Maintenance to talk through your project.

More Extension Advice

Looking for more advice before starting your project?

Keep an eye out for other posts:

5 Design Mistakes to Avoid When Planning a House Extension

5 Contractor Mistakes Homeowners Make When Building an Extension