Extensions: What Can I Build for my Budget?

We take a closer look at recent extension projects featured in Build It to see how you’ve been adapting existing properties
by Emily Smith
5th May 2020

If you’re looking for a larger home, it could be more cost effective for you to add space to an existing property rather than move house or even self build. Before we investigate some recent projects, how much they cost and what they involved, here are some key ways to get the most out of your home improvement venture:

Identify your needs: Think carefully about your reasons for extending – are you looking to add more general living space or do you want a room with a specific purpose, such as an extra bedroom? Thoroughly considering what you want from the finished addition will help to form the foundations for coming up with a suitable brief and design.

Set a brief: Once you’ve determined your motivations and how you intend to use the new space, consider how your property will best respond to the addition. Key areas to focus on are establishing the potential ways that you could maximise space and natural light.

Work with skilled designers: While you may choose to come up with plans yourself and work with a structural engineer and a good builder to fine tune the details, an architect or experienced designer’s flair will help you get the most out of your home improvement project.

Assess the opportunities: When you talk it through with your designer, you’ll probably have a vision for how you think your home can be tailored. Keep an open mind and be flexible – it may even work in your favour.

Consider the rest of the house: A home extension project will add valuable new living space; but the results can be maximised if you go back to basics and consider how you really want to live in your home. The most successful schemes tend to include layout changes and renovation work elsewhere in the house, too.

Cost versus value: It can be easy to get carried away with all the exciting extension possibilities, but take a moment to step back and have a look at how much value it will add to your house. You might have different priorities if this is your forever home, but as a rule, try not to spend more on a property update than its finished value.

Investigate local house prices to get an idea of what uplift you can expect; and check out the Office for National Statistics’ handy extension value calculator to get a quick idea of the potential increase in value.

Understand the planning rules: You may not actually need to submit a formal planning application thanks to permitted development (PD) rights. But if your house is in a designated zone (such as a conservation area or an area of outstanding natural beauty) or if the property you’re proposing to extend is listed, your PD rights are restricted.

Read more: Guide to Permitted Development

Create a project schedule: While it’s inevitable for there to be a few bumps in the road, by and large, a well-organised scheme should come together smoothly with minimal changes needed as you go along.

Protect your project: Ensuring you have the right insurance in place for your extension scheme will protect the new works and the original building from anything that could go wrong during the build.

Engage skilled builders: When you put the scheme out to tender, be sure to provide enough detail to compare quotes like-for-like. Given a basic outline, one contractor may over-specify to cover all margins, while another might quote cheaply knowing they’ll charge extras – so provide a clear and comprehensive brief. Busy builders may quote higher, but remember they’re busy for a reason.

Efficient management: Whether doing it yourself or bringing in a professional, it’s important for the project manager to keep a tight rein. It’s their job to make sure things are done to a high standard at the pace you need.

What can you get for your budget?

To help you get a sense of what size and quality of extension you could achieve for your money, Build It has taken a closer look at nine of our most popular extension projects (many of which also included renovating the rest of the house).

£88,255: Hands-on revamp

Open-plan kitchen extension to a Victorian home

Property style: Victorian Extension

Construction method: Steel frame, brick & block

Extension size: 33m2

Dan and Miriam Nethercott found themselves feeling their home to be short on space to accommodate their growing children. While they had already made significant improvements to their 19th-century house, they thought an extension and renovation could create a home better suited to family life.

To cut costs, Dan took on the role of project manager, engaging a small contractor to carry out most of the work onsite. He even turned his hand to DIY projects too, sourcing a staircase post on eBay and undertaking as much of the interior fit-out as possible.

“Personally, I’m always surprised when people spend lots of money paying professionals to do things like decorating,” says Dan. “You can teach yourself to do the basics adequately – I actually quite enjoy doing it!”

Read the full story

£110,000: Geometric oak extension

Contemporary extension at the rear of a an edwardian terrace

Property style: Edwardian Extension

Construction method: Oak frame, reclaimed brick & rubber

Extension size: 14m2

Egon Walesch and Richard Goodwin saw an old lean-to at the back of their Edwardian terrace as the ideal opportunity to create a contemporary sunroom. Eager for the oak extension to harmonise with the main house, part of the addition is clad in reclaimed yellow stock bricks in keeping with those of the period property.

The thrifty couple’s knack for upcycling helped to keep interior costs low. A talented upholsterer, Richard gave a new lease of life to furnishings that he sourced from auctions and online markets. Remarkably, a piece of salvaged driftwood from the Thames was even refashioned into a mantelpiece.

“We feel extremely proud that we’ve created a wonderfully unique home while still celebrating the property’s original charm and character,” says Egon.

Read the full story

£161,000: Two-storey addition

contemporary mill conversion

Property style: Rebuilt stone mill conversion

Extension construction method: Steel frame

Extension size: 100m2

Roy and Marianne Stenhouse have created a striking modern addition to their 400-year-old mill, which was rebuilt into a home 10 years previously. Following the arrival of their two children, it was clear that they were in need of a brighter, larger space. Nikki Ritchie of Hyve Architects presented the couple with a 3D plan that ticked all of the boxes.

To ensure the build remained on budget, Roy project managed alongside a local contractor, embracing the task of wiring up the entire house with a smart system. Another frugal measure was the family’s decision to remain in the property during the project. “We managed to live in our upstairs living room; the kitchen was unaffected as we planned to move it later on,” says Marianne.

Read the full story

What does it cost to extend?

Prices vary widely depending on the size, design, spec and which part of the country you’re building in. As a general guide, you can expect to pay at least £1,200 per m2 for a basic-quality, single-storey addition – but this could stretch upwards of £2,500 per m2 on a top-end scheme.

As a rule, multi-floor extensions should be similarly priced for the same amount of space. This is because, even though you’re building upwards, you obviously won’t need as much foundation or roof (often the most expensive part of a project) as you would with a ground-level addition.

When briefing your designer, it can be tempting to be cagey about what you have available to spend. However, if you give them a clear budget (minus your contingency) then they’ll be better able to assess what you are realistically able to achieve for the money you have at present.

A good professional will of course aim to deliver the wow factor – but above all they should create the space you want at a price that you can afford. Remember that if you’re looking to turn a profit you need to have a clear picture of how much it will cost versus the value of the finished house.

£200,000: Bungalow to family home

Bungalow extension

Property style: Bungalow

Extension construction method: Timber frame

Extension size: 114m2

Adam and Karla Bradstock bought a detached bungalow with a view to working on it slowly and saving money to pay for elements as they went. The couple added another storey and completely remodelled the ground floor.

Putting his experience of running a construction and landscaping company to use, Adam assumed the roles of both architect and construction lead. Neighbours let the Bradstocks live at their home while they were away in exchange for landscaping services, while friends and family in the building trade volunteered their help.

Mounting pressure to make the home habitable meant they had to take out a loan to boost their budget. “We think our scheme might have cost double what we’ve ended up paying if Adam hadn’t done the work himself,” says Karla.

Read the full story

£275,000: Contemporary revision

Contemporary Bungalow renovation and extension

Property style: 1960s bungalow

Extension construction method: Brick & Block

Total house size: 271m2

Mark and Stephanie Fernandez had an array of projects under their belt already when they took on the renovation of a dated 1960s bungalow. A commercial property developer and chartered surveyor, Mark kept a close eye on costs via detailed spreadsheets. This was especially important seeing as the family continued to live in their previous home, rather than selling to finance the build.

Despite their fastidiousness, they encountered unexpected hurdles, including ill-fitting windows and a cantilevered staircase that was incorrectly measured. Luckily, the couple had a contingency fund to fall back on which helped to rectify these flaws. “Always add a month to your timings and 10%-15% to your budget,” says Stephanie.

Read the full story

£310,000: Open-plan living

Renovation & Extension of a Period Home

Property style: Victorian

Extension construction method: Brick & Block

Total house size: 235m2

George and Rosie Woods sought expert guidance when transforming their rundown late-Victorian building into a stylish and energy efficient contemporary home. With sustainability in mind, the couple consulted Green Tomato Energy and visited the NSBRC in Swindon to consider their options.

“We wanted to know what to spend money on in order to make the house as thermally efficient as possible,” explains George. “All the experts that we spoke to said that it
was essential to prioritise the insulation and airtightness. We classed the other elements as non-vital ‘nice to haves’.” An extension on the ground floor now houses a a split-level kitchen-diner and living room, while a new basement room is used for storage.

Read the full story

£375,000: Glazed Extension

Extension and conversion project

Property style: Victorian

Extension construction method: Brick & Block

Total house size: 110m2

Richard Ball transformed this Victorian workshop into a three bedroom house with the help of Hayward Smart Architects. “We wanted to retain the structure in its present form and character, and extend with a contrasting single-storey contemporary addition, linked by a very lightweight, fully glazed entrance lobby,” explains Richard.

The new sleek addition has been designed as a high quality, modern building that cuts into the sloping site, reducing its impact on the setting.

Read the full story

Loft conversions

A well-conceived project extending into your loft can be one of the most effective routes to adding value to your home, with the potential to give a 20% return on your investment if you get it right.

The key factors that will affect the overall cost of bringing living space into this storey include the size of the area you’ll be creating, the nature of the roof structure, the type of conversion and the level of internal finish that you will require. If you’re planning to fit a bathroom, for example, then this will involve more plumbing work as well as extra costs for sanitaryware and fixtures.

You’ll also need to bear in mind that alterations may be required on the lower floors to enable the development, such as inserting a new stairwell and providing a point for fire-safe access. In some cases, you might even need to shore up the property’s foundations by underpinning.

Location has an impact, too: for instance, you might currently pay around 15% more for works in London compared to most of the UK; but 5% less in areas like Wales or the north east of England.

Remember that every project is unique, so it’s vital for you to undertake a full costing exercise at the planning stages in conjunction with your designer, main contractor or specialist loft company. This will help to ensure that you can complete a project within your budget; and that the finished result is worth at least as much as what you paid for the conversion.

Obtaining a second opinion, for instance via the Build It Estimating Service, is a wise choice. This will give you peace of mind that the project is going to be affordable, not to mention providing you with a sound cost plan against which to judge quotes from trades.

Read our complete guide to loft extensions

£507,000: Sixties remodel

Stylish renovation and extension to a 1960s property

Property style: Mid-century modern

Extension construction method: Brick

Extension size: 86m2

Catherine and William Allen have breathed new life in to a 1960s dwelling in Oxford. The couple set aside a budget of £250,000 to cover the works, and after putting the project out to tender, opted for the lowest quote.

However, a contentious relationship with their builders resulted in a walk out, with the family forced to move into a half-completed home. “Thankfully we weren’t paying for anything upfront and they did return,” says Catherine. The build cost double their budget, but it still managed to turn a profit and the Allens are pleased with their home.

Read the full story

£650,000: Luxury transformation

Modern Art Deco style home with pool

Property style: 1930s

Extension construction method: Brick & block

Total house size: 278m2

Hayley and Harry Upton made an impulsive purchase when they took on a 1930s home in need of TLC. With Hayley working full time, project management of the home improvement scheme was entrusted to their builder, a decision she now sees as a mistake. “I would come down on a Friday to see how things were progressing, but realised after a few months that I was being taken advantage of”, Hayley explains.

Luckily, a family friend and retired builder stepped in, but unfortunately costs had already spiralled out of control. Indefatigable, Hayley used her initiative and travelled around the country to source high-end finishes on a shoestring budget. “I never give up and I’ve learnt a lot along the way. I carried on and we got there in the end,” she says. The project transformed the original three bedroom property into a six bedroom, open-plan family home.

Read the full story

£414,000: Glazed extension

Modern kitchen in glass extension

Property style: Edwardian

Extension construction method: Steel frame & glazing

Extension size: 15m2 glazed extension & 5m2 side extension

Liz Ashley and Brendan Bracey managed to negotiate an impressive £200,000 off of the asking price of their four-storey Edwardian house. Work on the home’s dated lower ground floor was put on pause for several years until the property’s value had increased, allowing a remortgage to finance the couple’s ambitious plans for a glass extension.

Determined not to exhaust their budget, initial drawings for an additional side extension were scrapped, lowering the contract price down to £345,000. However, following the structure’s completion, there were reservations about the lack of space. “In the end the architects came up with a simplified design that we could just about afford,” says Liz. “But I’m glad that we invested the extra money because the new space is open and clutter-free – which is exactly a what I had wanted all along”.

Read the full story

Glazed extensions & conservatories

A successful extension does more than just add to a house’s footprint. In fact, being able to bring more natural light indoors and create a closer relationship between inside and out are often key elements of the brief, too – which is why the glazing is usually a critical element of any design.

Traditionally, conservatories and orangeries were stand-alone add-ons to a home (and when they are designed in such a way today, they are treated differently for Building Regulations purposes). These days, however, homeowners usually want any new addition to flow directly from the original house, opening up the downstairs layout to create a single, large communal space featuring lots of glazing that offers ample daylight.

Although definitions differ, a conservatory is considered to have an all-glass roof and walls that are also largely glazed; orangeries tend to have a solid roof, sometimes punctuated by one or more glazed lanterns, and solid parapet walls. A mix of materials – glass combined with a timber, aluminium or PVCu frame, as well as exposed brick and render, for instance – will help to give these buildings their character.

Contemporary architects are continuing the trend, offsetting swathes of glazing with materials such as timber, zinc and stone. Whatever the style, using lots of glass will bridge the gap between house and garden, and cleverly chosen design and materials can amplify that link.

What’s more, advances in glass technology have made heavily glazed extensions a viable option for year-round living. No longer seasonal spaces, these zones can now be light-filled sun-traps that don’t overheat; exactly the kind of place where homeowners want to spend all their time.

Top image: Hayley Upton took on a tired seaside house and extended it to create a spacious luxury property. Read more

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