User guide
Finding your way around the guide
To navigate between pages, click or tap the arrows to go forwards to the next page or backwards to the previous one. The arrows can be found either side of the page and at the bottom, too (circled in green, below).
Menu/table of contents
Click or tap on the three horizontal lines in the top-right of your screen to open the main menu/table of contents. This icon is always visible whether you're using a computer, tablet or smartphone. The menu will open on top of the page you’re on. Click on any section title to visit that section. Click the cross at any time to close the table of contents.
Text size
On a computer, you'll see three different sized letter 'A's in the top-right of your screen. On a smartphone or tablet these are visible when you open the menu (see above). If you’re having trouble reading the guide, click or tap on each of the different 'A's to change the size of the text to suit you.
Pictures
On some images you'll see a blue double-ended arrow icon. Clicking or tapping on this will expand the picture so you can see more detail. Click or tap on the blue cross to close the expanded image.
Where we think a group of images will be most useful to you, we've grouped them together in an image gallery. Simply use the blue left and right arrows to scroll through the carousel of pictures.
Links
If you see a word or phrase that's bold and dark blue, you can click or tap on it to find out more. The relevant website will open in a new tab.
Jargon
If you see a word or phrase underlined, click or tap on the word and small window will pop up with a short explanation. Close this pop-up by clicking or tapping the cross in the corner.
Help
On a computer, you'll see a question mark icon in the top-right of your screen. On a smartphone or tablet this is visible when you open the menu (see above).
Clicking or tapping on the question mark will open this user guide. It opens on top of the page you're on and you can close it any time by clicking or tapping the cross in the top-right corner.
Making extra space
An extension or renovated loft gives you a brand-new room that provides extra space, looks great and adds value to your property.
What to consider when considering extensions
Extending the home you know and love may be cheaper and less of an upheaval than buying and selling, but it requires planning, time, patience and investment. Whether you’re considering a simple garage conversion or you fancy going the whole hog with a double-storey extension that enlarges the footprint of your property, read on to find out more about what steps to take and in what order.
The Royal Institution of Chartered Surveyors quotes £32,000 as an average cost for a single storey flat-roof extension and more than £100,000 for a two-storey pitched roof with a couple of windows.
Regardless of the type of extension you go for, you'll likely need to think about planning, budgeting, choosing the company that does the work, building regs and planning permission. Here we touch on all of these themes and give options for delving deeper.
Who will design and build your extension?
You can choose to design it yourself, opt for a building and design company or work with an architect. Choosing the right person to draw up your plans is as important as choosing the right builder.
The key is to do your research, look at previous work and ideally speak to past clients. Choose someone who most closely aligns with your design aspirations, and who you feel you can work with best. The same goes for picking a builder.
Choosing an excellent company to undertake a large-scale home improvement such as an extension is a crucial step in the process. Find a local company that has been vetted and approved by heading to Which? Trusted Traders.
Building regs and planning permission
Take a look at Planning and budgeting for information on your responsibilities in these important areas. We also have in-depth guides from our Trusted Traders that explain in detail when you need to apply for planning permission and how to avoid falling foul of building regulations.
Timeline
How long the work takes will of course depend on the type of extension you’re having done. Laying out a timeline will give you a better understanding of what’s involved and how long each aspect can take. Our building an extension timeline guide refers to a single-storey extension, from laying down the foundations to finishing the plastering, but it can easily be tweaked for other types of extension.
Saving and spending on your conversion or extension
Design
- SAVE: Use 3D software to draw up your plans and help to visualise what you want the space to look like and what would work best for you. This will help when you speak to an architect.
- SPEND: Speak with an architect – although you’ll have to pay for this service, it could save hundreds later as it will make clear what you want to do with the planned space and therefore what sort of conversion to go for. Cover questions such as staircase position (for basement and loft extensions), plumbing, walls and heating.
Insulation
- SAVE: In some cases, such as a loft conversion, you may be able to install the insulation yourself.
- SPEND: Professionally installed insulation will be necessary for most other extensions. If a professional does your loft insulation, it should take around four years to pay for itself (if going from no insulation to recommended thickness).
Fixtures and materials
- SAVE: Buying off-the-shelf is cheaper than custom-made, but you can find ways to customise items to get the look you want. Check second-hand and auction sites such as eBay and look out for seasonal sales. Your builder might be able to offer discounts, too.
- SPEND: Get your window choice right – both the number and type. Would fewer, larger windows be acceptable rather than the pricier option of more smaller ones?
Project management
- SAVE: Make sure you know what needs to be done, when and by whom. Create a timeline and book in the relevant tradespeople. Look at several quotes for each part of the work and compare like for like.
- SPEND: Pay for a conversion company to manage the work.
Sign off
- SAVE: If your extension or conversion is near the boundary with your neighbour, get the party wall agreement sorted at least two months before you start work. This is written consent from any neighbour you share a wall with that they accept your plans – this covers the changes you’re making and also how long it will take.
- SPEND: If you don’t agree with your neighbours, they can appoint their own surveyor and it will become more expensive for you. Party wall agreements can cost around £1,000, so set aside money for this.
Could a garden room work out more cheaply than an addition to your house? A luxury space with double glazing, patio doors and heating, including installation (but excluding utilities) can be constructed for less than £30,000.
Extension checklist
Run your eye down our checklist before committing to your extension, and avoid being caught out by extra hidden costs.
-
Make a list of everything you would like included, then compare your quotes item by item when pricing services and materials.
- Always check that VAT is included.
- Set aside around 10% of the total cost for unexpected extras.
- Fit-out costs, for things like kitchen units and goods, utility room furniture, sliding doors, underfloor heating, will be additional.
- Having a building contractor or architect manage your project will cost more. Budget for architect design fees being up to 10% of the construction cost.
- Planning drawings, construction drawings, a measured survey of the existing house and a structural engineer to size roof joists and foundations will all cost extra.