About us


ExtensionPlanner.co.uk is a Sussex-based extension and home remodelling design practice run by Lizzie and Peter Smith We work across the counties of Sussex, Surrey, Kent and Hampshire, and specialise in helping our clients take an idea for making their homes bigger, work out the best way to do it, and help them get planning permission, while making sure it is also going to be practical to build, and comply with building regulations.
We're a happily married couple who discovered we share a love of architecture and home design, when we walked around our first prospective home together, almost 30 years ago. Despite it being a total wreck, we both took one look, and said 'this is it.' Since then we've done up several homes of our own, undertaken successful property developments, and helped clients get planning for a wide range of projects from a Pool House to a 7-bed luxury Sussex-style home.

Peter started his career by training as a Chartered Surveyor, learning the ins and outs of building construction. He then developed a successful career in marketing and media, doing property development as a sideline. With just about every build people asked us 'who's your architect?', and before long we found ourselves drawing up plans for friends and family. After our first few commissions, we launched extensionplanner.co.uk about five years ago.

Lizzie is one of the most intuitive and visual designers you're likely to meet, bringing her artist's eye to bear on every interior, not just making sure it encourages flow and movement, but choosing materials and colours that hang together to create energetic, yet restful homes. Her work has appeared in numerous home magazines, and she brings a rare ability to see and imagine how you will live in your new space.

It's all about creating a design for living

Here are a few pointers that you need to bear in mind when designing any alterations to your property. There picture beside each one clicks through to a project case study where this can be seen in practice.



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Making rooms flow

Especially in smaller properties the way you design a room to make sure you get all the elements in and have room to move and use them is critical. Get it wrong and it appears cramped. Get it right and even a small room feels spacious.

The same is true of every room in the house, which is why we will often show how items of furniture, such as beds, tables and sofa will fit into the space to make sure you're not going to end up cramped.


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The importance of windows

Windows can make or break a property. Profile, nightlines, matching, materials - these are all key considerations and will form part of your materials schedule so they need to be functional and look the part.

We do tend to recommend hardwood or aluminium, especially for bi-fold doors, and we know a number of specialists that can custom make window joinery to give you the perfect result, and often for far less cost than you might expect.


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Fit for your life

As we evolve in life, our homes need to do so as well, so we look at how you are living now and how that might change in the medium term to make sure you and your home don't outgrow each other.

A lot of extensions now are designed to add on useful space, such as kitchens, guest bedrooms, always with ensuite, garden and family rooms The key is to work out how you want to use it now, and how it will adapt to your needs as you live in the home..


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Hiding the joins

Nothing says 'I'm an extension' as loudly as an RSJ beneath the ceiling. Look at the pic on the left and if you hadn't designed the steels you wouldn't know there's the best part of a ton of RSJs up there.

A good builder will be able to 'lose' most steels into the ceiling, provided you specify they should go there, and it makes all the difference to the success of the project.


Building schedule
Nailing the schedule and price

If you want any chance of getting a fixed price, and staying anywhere close to it, you need a detailed schedule of what the builder has to do in each room. This is the basis of your contract with them, and anything detailed needs to be included so they can price the job up accurately..

This will cover all the minutiae from where plumbing and electrics need to go to the extent of works and making good. Remember, if it's in the spec, the builder has to deliver it, but changing your mind adds cost, so this is a document worth the time taken to get it right.


Extending a house isn't cheap, but the right extension will turn it into a home for life.

We specialise in helping our clients design the kind of homes that will be the envy of their friends. In fairness there are a fair few that we would be happy to live in ourselves.