15 things to consider before starting your home extension.

House extension guide - 15 things you need to know

Extending your home is a great way to increase space, improve flow and functionality and add value to your property. The costs involved with moving to a new house can be substantial, so it is easy to see why many homeowners are staying put and deciding to renovate instead.


Whilst there are many benefits to extending, there are also pitfalls to be aware of. This is especially the case if you are new to home extensions. So before you get started with your next project, check out fifteen questions to consider in our helpful house extension guide below – to make sure your build gets off to the best start!

1. Why do you want to extend your home?

Before you commit, make sure you are clear on your reasons for undertaking the project. Why is it that you need extra space and what are you hoping to achieve? Is it more lounge space, a lighter brighter kitchen or a better flow to your home?

Consider this.

Even for a seemingly simple task of adding a bedroom or home office, consider how you use the space now, what “future-proofing” may be advisable and whether it will add value to your home. Having a defined purpose will help establish clear plans and design choices, ensuring you don’t regret decisions further down the line.

2. Will your plans add value to your property?

As with any home renovation, make sure you have considered whether your plans will ultimately add value to your property. Even if you are planning on staying put for the long-term, check-in with a local estate agent who can advise on what buyers are looking for in your area.

In addition.

Ensure that the added value is greater than the projected cost of the project, bearing in mind the ceiling price of your street or neighbourhood. You never know what the future might hold, so make sure that your extension is helping you out in the long run.

3. Have you established your budget?

Before talking to architects and builders, establish what you can afford to spend. Having a clear budget will keep plans realistic, with professionals further able to advise on what costs are involved and what’s possible for your project.

Once you have received quotations, compare these item by item to ensure value for money – remembering to check if VAT is included in the pricings. Don’t forget to also add a contingency of 10-20% to your projections, as home extensions notoriously throw-up unexpected issues.

4. Do you have the relevant permissions in place?

If you’ve spoken with architects, surveyors and builders – and you are now at the permissions stage – don’t underestimate the importance of this step! Some projects can take place under permitted development rights (unless your home is a listed property or in a conservation area), for instance a rear wall of a detached property can usually be extended by eight metres for a single storey property and three metres if it’s double storey.


It is always advisable to check with your local planning department before starting any work however, as applying for retrospective planning permission can be a stressful and time-consuming task.

5. Have you considered Building Regulations approval?

Even if you are certain your home extension can be constructed under permitted development rights, don’t forget that any project will require Building Regulations approval. This includes minimum requirements for things such as fire safety, structural integrity, energy efficiency, ventilation and dam proofing.

Almost all home extensions will require approval, especially for projects that include installing new plumbing for bathrooms or kitchens, new chimneys, altering window openings or replacing loadbearing walls.

6. Have you informed your home insurance provider?

Before starting your extension, make sure you have informed your home and contents insurance provider – and that your policy will cover any works you are planning to undertake. Such projects are likely to increase the rebuild cost of your home (a factor considered when pricing premiums) with work potentially putting the structural integrity of your property at risk. If you don’t tell your insurer and anything were to happen during building works, your existing policy could be void.

7. Do you need to employ an architect?

Depending on the scale of your home extension, you may not necessarily need an architect. Do bear in mind that architects can help with drawing up plans (useful for putting plans out to tender with building contractors) as well as advise on design, what’s achievable for your budget and even project management phases.

In addition.

If you are seeking professional help, make sure to give detail as possible on the project at the first meeting (including your aspirations, timeframe, budget etc.). Communicating clearly defined goals from the outset will help all parties involved.

8. How can you select the best architect for the project?

Most architects and architectural firms offer a free initial consultation. When researching architects, check they are registered with the Architect’s Registration Board (ARB). Membership of the ARB is compulsory and making sure they are also part of an accredited RIBA Chartered Practice (Royal Institute of British Architects) will provide further assurance.

You may also consider their previous work.

For instance, if you are looking for a small extension, it may be a problem if they work exclusively on large-scale projects. Many architects will have their own signature style, so think about whether this matches your own.

9. How can you find the right building contractor?

Unless you have experience working with a particular building firm, it is a good idea to seek out several quotations for your extension. Put your plans out to tender, thinking about reputation and reviews, interpersonal relationships and budget (not just the lowest price!).

Different options.

You can opt for a main contractor for the entire project or hire various trades and sub-contractors. Builders should also offer details on specifics such as your ‘defects liability period’ and timescale for post-completion fixes. If you’re not sure about anything, just ask.

10. What type of extension would be best?

There are myriad different ways you can extend your home – from loft conversions to single and double storey additions or even “floating” cantilevered extensions. Think about the overall look of your home (both interior and exterior) as well as just the extra space. Often the cost of a two-storey build isn’t that much more than a single-storey.

In general, however.

The more bespoke and unique the build, the higher the price. If you are thinking about creating another floor over an existing structure, do make sure to have a full structural survey – as sometimes the existing building and foundations might not be up to scratch.

11. Have you created a schedule for works?

Before your home extension gets underway, draw up a schedule of works. You can either do this yourself, or with the help of an architect, contractor or project manager. The schedule should list what works need to be completed and in what order, breaking the project down into phases. Without careful planning, extensions can potentially become difficult with tradespeople overlapping and time being wasted.

As part of this process.

Set a firm completion date (specified in writing) with your builders. Having a schedule will further help with decisions on whether moving out of your property is appropriate, and how long this might be for.

12. How much glass can you use?

Selecting your materials is one of the most important structural and design considerations. One of the most common aims of any extension is increasing natural light. This means homeowners are often keen on large amounts of glass.

Do consider the potential issues though.

For instance, in some poorly designed conservatories or glass-roofed structures, the space is only usable for certain parts of the year. Furthermore, Building Regulations often limit the total area of glazed elements to a maximum of 25% of the extension’s floor area. This can pose a problem for smaller extensions, so do make sure to consult professionals if you are concerned about the materials in your build.

13. What could an interior designer help with?

Interior Designers can help with decoration schemes large or small. Are you struggling with questions such as if you should leave the beams exposed, floorboards painted, what about brickwork or kitchen design? How well the new space sits alongside your original property will be a key marker of success.

With professional assistance.

You can improve the overall aesthetic and flow of your home (whether that’s adjusting layouts, introducing clever storage solutions, colour-schemes or accent lighting). This can be especially useful if you are extending to add value. If you are wondering where to start, the Chartered Society of Designers offer a “find a designer” service.

14. Should you stay living on site?

Depending on the scale, timings and complexity of your build, it may be perfectly acceptable to remain living on site. Despite this, many homeowners find that moving out is the best option. Given that more of us are working from home now, consider if the noise and dust will impact your work or family life – and in turn, whether you might slow down progress.

Staying with family or friends, holiday homes as well as short-term rentals are all options, even for just the most significant parts of the project. Adding an extension is also the perfect time to think about larger-scale refurbishments, so moving-out temporarily could help you transform the entire property.

15. Have you spoken to your neighbours?

Last but not least, of particular importance in built-up areas, is talking with your neighbours about your plans. Keeping those living closest to you onside will make for a far simpler and less-stressful build. Think about the access you require and keep your neighbours up to date on developments as much as possible.

In addition.

If your project involves foundations close to the boundary of your property, you’ll likely have to comply with the Party Wall Act. This will come with specialist surveying requirements and further associated costs if disagreements arise.

Final thoughts.

Whether your home extension project is large or small, careful planning is the key to any build. From gaining the relevant permissions to considering materials, choosing architects and builders, informing neighbours and establishing budgets and timeframes, there’s lots to navigate. Taking these questions into consideration will ensure that your extension gets off to a flying start.

Thank you for reading our House extension guide!