All you need to know about extending, from planning permission to cost and sympathetic design
Many of our clients love the location of their home, or want to skip the hassle of relocating. That’s why they come to us looking for advice on a house extension.
This guide by Paul Moore, Director of McCann Moore Architects, deals with everything you need to know about modern home extension design in Northern Ireland, whether your home is several storeys high or a bungalow.
Our clients come to us with different requirements for their house extension. Our most-requested design project is an extension to a detached home. Typically, our clients want to add to their living space.
A rear (or sometimes also side) extension is often the best way for our clients to get a spacious, open plan living space on the ground floor, plus extra multipurpose space upstairs. Frequently we open up the kitchen/living area to the back garden.
How big can my house extension be without needing planning permission?
Permitted Development Rights are reasonably generous in Northern Ireland. You can achieve a LOT with an extension within your Permitted Development Rights.
You can extend your detached property by 4 metres for a single storey extension and 3 metres for two storeys within your Permitted Development Rights. This new extension must come from the main bulk of the house, and not be an “extension of an extension”.
In many cases, your extension can be the full width of your house. Certain rules apply in terms of height and boundary conditions. It’s best to talk this over with an expert. Remember that if you go full width, you need to consider access to the rear of your house. Builders will need access for the duration of the project, potentially with bulky equipment. And you will need access once the project is complete.
By the way, if you live in a conservation area, you’ll always need Planning Permission, regardless of extension size. Read more about planning permission when working with an architect.
Do I need building control approval when extending?
It’s safe to assume you do. Nearly all works require Building Control Approval in Northern Ireland – even if you’re simply changing your boiler or adding a fire.
Planning Permission is a different matter. If you’re wondering what size extension you can build without needing Planning Permission, see above.
How high should we go with our house extension?
If you need the space, building higher can be more cost effective than having a similar amount of space just on one storey. That’s because you can save on expenses like foundations and roofing materials when you go up. You also avoid the usability trap of creating imbalanced areas in your home – a huge ground floor living area, but small, poky sleeping areas upstairs.
Increasing the height of your extension means you can also preserve more of your outdoor space.
So much for the pros. What about the cons? Your neighbours might object more readily to a double-height extension than to a single storey. And if you’ve set your heart on roof glazing or skylights flooding light into your ground floor kitchen for example, doubling the height can compromise this design feature.
Remember that height affects Planning Permission, so always ask an expert.
Belfast City Council has a useful guide to the rules around residential extensions and alterations if you want to know more.
How much does it cost to extend a house?
The proverbial piece of string comes to mind. The honest answer is – it depends.
What space do you want to create? For example, if you’re extending to create a brand new kitchen, the cost will probably be higher than a room that doesn’t need an extensive fit-out.
Remember – while a decent builder might be able to give you ballpark figures early on, you can only really get an accurate price for your extension once potential builders have seen complete working drawings. A good architect can guide you through this tendering process. All builders are not equal! The cheapest quote is not always the best (or the least expensive in the long run).
Here’s a tip that many of our clients don’t know. If a property has been vacant for two years, VAT on your building cost reduces from 20% to 5%. Similarly, if you convert a house of multiple occupancy/flats back into a single dwelling, VAT also drops to 5%. If this applies in your case, you can make big savings on the cost of your extension.
Talk to an architect early on in the process. They can give you a good idea of price range per square metre for your planned extension.
What type of extensions are the most popular?
The most popular projects we see among our clients are rear home extensions and, to a lesser extent, side extensions. If you’re thinking of a loft conversion, remember that’s a budget-friendly option that often doesn’t require an architect. We also don’t see the basement extensions typical of bigger cities like London, simply because land is more easily available and less costly here in Northern Ireland.
What aspect should my home extension be?
This is something we give much thought to as architects, because a rear extension necessarily faces in one fixed direction.
With your architect, you should consider whether the rear of your property faces north, south, east or west. For example, an abundance of glass in a south-facing rear extension can overheat uncomfortably, even in Northern Ireland! Meanwhile a rear extension that faces a more northerly direction might benefit from as much light as possible. Glazing can be a major cost, so it’s worth getting an architect’s eye on the aspect of your potential extension.
What about the original footprint of my house and garden?
Will an extension make the original rooms in your house darker? It’s worth making sure this doesn’t happen!
A good architect will help you make the most of the natural light. Glazing is a huge design dilemma in both rear and side extensions. An architect can also help you make sure that the new extension blends seamlessly with the interior of your existing house. You might also need to reconfigure your existing layout when you extend – architects help with this all the time.
Think about the view too. Many of our clients want to lead the eye into their garden. We help them do that with glazing and clever choice of materials, for example, floor finishes that can be replicated indoors and outdoors. You might also need to adjust the height between indoors and outdoors (or existing footprint and extension) to avoid clunky-looking steps or changes of level. The other thing we like to weigh up is how to keep a pleasing balance between indoor and outdoor space. We’ve all seen those massive developer homes with postage-stamp gardens. To be avoided!
What exterior finish on my extension will withstand the Northern Irish weather?
External wall insulation is fantastic now – we use it a lot on our house extensions. It’s like wrapping your home in a blanket. Ask your architect at the design stage how to incorporate the latest insulation products into your project. It means you can add high-end design finishes like cedar or metal-cladding without compromising on heating costs.
Remember to consider maintenance and cleaning costs for your exterior finish too. Your extension might need regular re-painting, or timber cleaning, depending on the finish you choose.
Should my extension blend in or stand out?
That’s a design conundrum. In conservation areas, the onus might be on you to create a seamless extension that looks like it’s always been there. Other clients choose to make a bold statement by contrasting period with modern styling, or contrasting finishes like brick with metal cladding. This is where you need expert design advice.
Is there another way to add space to my home?
Actually, a good deal of our renovation work involves the creation of more space, as well as sympathetically rejuvenating the original building. Find out more about renovation design for your Northern Ireland home.
What else should I consider?
Disruption – some extensions are more disruptive than others. And some extensions, for many reasons, take longer than others. Chat to your architect about seasons and weather too. Northern Ireland offers no guarantees, but it makes good sense to plan to keep severe weather disruption to a minimum – a Belfast architect will understand this all too well!
Heating – you might need to change or upgrade your existing heating system to cope with the new space.
Neighbours – you know best how to handle this. We suggest speaking to them early on, and keeping them up-to-date as your project progresses.
At what point should I talk to an architect about my house extension?
As early as possible. It will make your decision-making so much easier. What prep do you need before talking to an architect? Often it’s enough simply to have a rough idea of your budget before you chat. If you can collect images of some extensions you like, that’s a good conversation-starter too.
Talk to the Belfast architects who understand your dreams
If you’re considering a house extension in Northern Ireland, we’d love to hear about your project. Every extension we’ve designed started with a conversation about a home that could work harder for the people living in it.