Is A Loft Conversion Cheaper Than An Extension?

Loft Conversion vs Extension: Which makes more sense for your home?

Many homeowners outgrow their space but aren’t quite ready to move. The big decision? Whether to extend outwards or make the most of your loft. This guide breaks down the real costs, planning rules, and space potential of loft conversions and home extensions, so you can choose the option that fits your home, lifestyle and budget best.

• Loft conversion vs extension: At a glance.
• Is a loft conversion cheaper than a home extension?
• Why loft conversions typically cost less
• How do I decide which options best for me?
• Frequently asked questions

Loft conversion vs extension: At a glance.

Not sure whether to go up or out? This quick comparison shows the key differences between a loft conversion and a ground floor extension. From cost and disruption to space and planning rules, here’s how they stack up side by side:

Is a loft conversion cheaper than a home extension?

Both loft conversions and house extensions offer real value when creating extra space. But which delivers more room for less money? Let’s break down the typical costs of each and explain why loft conversions often come out ahead regarding affordability.

Average loft conversion costs

Loft conversions come in all shapes and sizes, and so do their costs. What you’ll pay depends on the conversion type, the build's complexity, and where you live. Here's what most homeowners can expect:

Basic Velux conversion – from £20,000

The simplest and most budget-friendly option. It adds roof windows and insulation without altering the structure. Great if your loft already has enough height and you want to create a usable space quickly.

Visit our detailed guide on velux loft conversion costs.

Dormer loft conversion – £35,000 to £55,000

A rear dormer adds valuable headroom and floorspace. It’s one of the most popular choices, maximum gain without major disruption. Ideal for bedrooms, ensuites, or a home office.

Visit our detailed guide on Dormer loft conversion costs.

Hip-to-gable or mansard conversion – from £50,000

These larger conversions involve reshaping the roof to add full-height space. They take longer and cost more, but can transform your entire upper floor. Best suited to semi-detached or terraced homes with sloped roofs.

Explore our full loft conversion cost guide for more detailed breakdowns by loft conversion type, size, and location.

Average house extension costs

Extensions give you space on the ground floor, but they often come with more disruption and bigger price tags. Here's a look at typical costs:

Which adds more to your home?

Loft conversions can increase your property’s value by up to 20%, making them a strong return on investment, especially when adding a bedroom or ensuite. Extensions often add more ground-level space, but come at a higher cost and longer build time. Ultimately, the value added depends on your location, layout, and the quality of the work

Explore our full Loft Conversion ROI Guide for more insight.

Why loft conversions typically cost less

Loft conversions are more cost-effective than house extensions for a few reasons. You’re building within your existing structure, which means fewer materials, less labour, and minimal disruption below.

No foundations required

Because you're building into existing roof space, digging footings or laying new foundations is unnecessary. This avoids expensive groundwork and makes the construction process much simpler.

Minimal disruption to your home

Most of the work is above your living space, so you can usually carry on with day-to-day life while the build progresses. There’s no need to dig up your garden or reroute drainage like with an extension.

Faster build times

A standard loft conversion takes around 6 to 8 weeks to complete. That’s typically half the time of a ground-floor extension, which means reduced labour costs and less time living in a building site.2

Fewer materials in simpler designs

Rooflight conversions and basic rear dormers use fewer materials and require less structural work. This keeps your overall costs lower compared to more complex extension builds.

Often allowed under Permitted Development

Most loft conversions, especially rear-facing dormers and Velux designs, fall under Permitted Development. 

That means you can avoid lengthy planning applications, fees, and approval delays, as long as your project stays within the design limits. A loft conversion usually offers the best value per square metre if you want to add a bedroom, home office conversion, or ensuite without stretching your budget.

How do I decide which options best for me?

Choosing between a loft conversion and a ground-floor extension isn’t just about cost, it’s about how the new space fits your home, lifestyle, and long-term plans. Use this checklist to help decide what’s right for you:

• What’s your budget? Loft conversions are often more affordable, starting from around £20,000, while extensions typically begin at £30,000 and can rise much higher.
• Do you want to keep your garden space? A loft conversion won’t touch your outdoor areas. Extensions, on the other hand, reduce garden or driveway space.
• What kind of room do you need? Bedrooms, ensuites and home offices suit lofts well. An extension might be a better fit if you want a larger kitchen, open-plan living space or utility room.
• Are there planning constraints in your area? Most loft conversions fall under Permitted Development. Extensions are more likely to require planning permission, especially in conservation areas or for side/rear builds.
• How quickly do you need the space? Loft conversions usually take 6 to 8 weeks. Extensions often take 12 to 16 weeks or more, depending on complexity.
• Will the investment boost your property’s value? A well-designed loft can add up to 20% to your home’s value. However, check local ceiling prices; some properties may have limited uplift potential regardless of the upgrade.
• Can you manage disruption during the build? Loft work typically causes less disturbance. Extensions often involve restricted kitchen or garden access during construction.
• Is your loft easily accessible and suitable? Low head height or difficult access might make a loft impractical without major changes. A home extension could be more straightforward in this case.
• Does your plot allow for an extension? If space around your home is tight, building out might not be an option, making the loft your best bet for extra room.

FAQs - Loft conversion vs Home extension

Here our experts answer the most common questions on whether a loft conversions better than an extension.

Can I do both a loft conversion and an extension?

Yes, it's possible to undertake both a loft conversion and a home extension on the same property. Combining these projects can maximise your living space and offer cost efficiencies when planned together. It's advisable to consult with your local planning authority to ensure compliance with regulations and to determine if planning permission is required. ​

Does a loft conversion add as much value as an extension?

Loft conversions can add significant value to a property, often increasing it by up to 20%, especially when adding a bedroom or bathroom. Extensions also enhance property value, particularly when they expand key living areas like kitchens or living rooms. The exact value added by either project depends on factors such as property type, location, and the quality of the work.

Which is quicker to complete?

Loft conversions are generally quicker to complete than extensions, often taking around 4 to 5 weeks. Extensions can take longer, depending on their complexity and scale. However, the exact duration for either project will depend on specific circumstances, including design complexity and site conditions. ​

Are there more planning issues with extensions?

Yes, extensions often face more stringent planning requirements compared to loft conversions. While many loft conversions fall under permitted development rights and don't require planning permission, extensions frequently need approval, especially if they exceed certain size limits or are in conservation areas. It's essential to check with your local planning authority before proceeding with either project.