Good planning is key to a hassle-free home renovation. Read on for our handy guide to how to plan an extension!

How to Plan an Extension in 4 Steps

The first step in how to plan an extension is working out what you want to build. Next, you can start talking to home improvement companies and researching planning permissions and building regulations. 

1. Decide What You Need

How to plan an extension starts with deciding the size, type and design. Maybe you want to extend the kitchen or living room, or create open plan living space? Or maybe you need a home office. Will you extend out the back or to the side? How many storeys? 

Start researching the costs of a home renovation, materials and suppliers early on as your budget will condition the size and design of your extension. As a rule, the more complex the build and installations, the higher the cost. As a guide, a single-storey rear extension costs between £60,000 and £130,000 and takes 10-12 weeks.

2. Find a Home Improvement Company 

A good home improvement company can help you determine how to plan an extension, so the next step is to find one. You can also work with an architect or designer now. The fees may seem like an added expense but they’re experts at making the most of the available space and light.  

Choosing a home improvement company is an important decision. Ask for recommendations, check review sites, shop around for quotes and ask about their availability. Beware of anything that sounds too good to be true. Some builders undercharge on paper but then run up costs throughout the job or, worse, do substandard work. Always ask for itemised quotes and a walk-through. A reputable builder will be happy to oblige. 

Other things to ask: 

• Whether they can handle planning permission applications and get Building Regulations approval. 
• If you can see photos or visit previous jobs they’ve done.  
• What communications you will receive and whether they work with a home renovation project manager. It’s this professional’s job to oversee construction and keep everything on schedule. They’ll also be your go-to person, saving you time, stress and money overall.   
• Whether you can do any DIY if you’re on a budget. Straightforward tiling, flooring and decorating is usually feasible if you’re the handy type.  
  
  

3. Check if You Need Planning Permission

Finding out whether you need planning permission is an essential part of planning an extension. The good news is, these days you can build smaller rear and side extensions under Permitted Development Rights (PDRs), so you don’t need to apply. 

Under PDRs, two-storey constructions can extend up to 3 m from the rear wall but must not come to within 7 m of the rear boundary or be higher than the original roof. 

If you notify your local planning authority, single-storey extensions can extend upwards by 4 m and outwards by 8 m for detached homes (6 m for other types).  

Side extensions (aka side returns) can’t be wider than half the original house or over 4 m. 

No extension can occupy over half your land or have balconies, verandas or raised platforms. 

You’ll need planning permission for anything that doesn’t meet these criteria. Also, note that the rules for PDRs are different for listed buildings and designated land (conservation areas, Areas of Outstanding Natural Beauty, etc.).   

To build up to or near a garden boundary or do major work on shared walls, you may need a Party Wall Agreement with neighbours.  

4. Comply with Building Regulations

Even if you don’t need planning permission, you must get Building Regulations approval. There are two ways to do this: 

1. Hand in a Full Plan Submission to the local authority building control or inspector for approval before you start work. The building inspector will also visit to check the work at different stages. 
2. Submit a Building Notice 48 hours before starting to inform the local authority you will comply with regulations. This is risker as you’ll only find out about any compliance issues during the first inspector’s site visit after you’ve started.  

For more advice about planning permission, Building Regulations and how to plan an extension, don't hesitate to get in touch in touch with us.