The True Cost of Kit Build vs Traditional Build Extensions

This podcast is aimed at homeowners, builders and architects. 

In this episode, Paul Bird cuts through the myths and reveals the true cost benefits of building home extensions with innovative kits like Structural Insulated Panels (SIPs) versus traditional brick-and-block methods. Drawing on over 50 years of experience—and a decade specializing in kit builds—Paul breaks down the key differences that homeowners need to understand before committing to their next extension project.

Discover how kit builds deliver superior structural strength, airtightness, and thermal efficiency while accelerating construction timelines. Learn the real cost breakdowns: why kit builds shift expenses from labour to materials, how shorter build times reduce overhead and finance costs, and why off-site manufacturing cuts weather delays and waste disposal fees significantly.

This episode provides a clear, evidence-backed comparison to help homeowners weigh the total cost of ownership—not just initial outlay—including long-term energy savings and reduced risk of budget overruns.

Whether you’re a homeowner curious about better building options, a builder exploring innovative methods, or a design professional seeking fresh insights, this episode equips you with the knowledge to build smarter, faster, and greener.

Listen now and get the facts behind the future of home extensions. Don’t forget to subscribe, leave a review, and share.

You can also visit KitBuilds.org.uk for more information.

Transcript

"Welcome to Kit Builds.Org.UK, the podcast that’s reshaping how Britain builds.

Whether you're a homeowner, builder, or architect, this podcast is your blueprint to smarter, faster, and more eco friendly home extensions, using cutting-edge panel systems like SIPs and modular kits.

I’m Paul Bird and I’ve spent over 50 years building home extensions and in the last ten years using SIPs and other kit builds. I’m here to cut through the noise, expose the myths, and give you the knowledge no one else is sharing.

Each week, we tackle real questions, real builds, and real results with clarity.

Build smarter. Build faster. Build for the future.

Now, let’s get to work."

Segment 1: Setting the Stage
Most people automatically think of traditional builds when considering home extensions—brick and block or block and block with a render finish, conventional construction. But kit builds, especially Structural Insulated Panels or SIPs, are changing the game. They offer a different cost structure and value proposition that many homeowners, and even professionals, overlook.

First thing we need to do is dispel the myths.

One myth is, kit builds are temporary or inferior structures; this just isn’t the case. In reality, kit builds match, and in many respects exceed, the durability and performance of traditional builds. Despite the lighter weight of a kit build extension, kit foundations are engineered to support equal or greater loads than conventional foundations, ensuring structural integrity without compromise. The walls constructed from kit components offer superior strength over traditional brick and block. As a bricklayer I was genuinely surprised at this, but I’ve seen the test results and structural engineers reports and for SIPs and the hup! system and they both out perform traditional builds, this also contributes to greater airtightness and enhanced thermal efficiency. Additionally, the accelerated construction timeline of kit builds not only reduces project duration but also maintains or improves quality standards.

This all aligns with the fundamental principles of construction—strong, reliable foundations and structural elements are critical, whatever the build method. Kit builds uphold these standards effectively while delivering added benefits in efficiency and once completed, building performance.

Another myth is builders charge extra and make more money. This isn’t correct at all, as you’ll hear in a minute the cost to build a kit build is similar to a traditional build. 

Where this mistake arises is with the profit made, let’s say a builder  can make £5,000 pounds profit on the average extension with a traditional build it takes 8 to 10 weeks to generate that profit but with a kit build it only takes 4 to 5 weeks. This means builders can double their profit without increasing their overheads such as employees, vehicles, insurance etcetera. Most importantly they can do this without charging any extra on individual projects so although the builders can make more profit in a year it doesn’t cost the home owners any more.

Segment 2: Breaking Down the Cost Components
When comparing costs, it’s important to look beyond just the upfront price of materials.

As a guide line, if you take out the VAT and any profit the cost of a traditional build is approximately one third materials and two thirds labour.  The cost of a kit build is the other way around, because a lot of work is done during manufacture approximately two thirds of the cost will be the kit and materials and one third labour. Now, this isn’t exact for every extension but as a rule of thumb it’s not far off. This means that most extensions are a similar cost to build which ever type you go for.

Project Duration:
Shorter construction time means less overhead and fewer temporary living inconveniences for homeowners, plus lower finance or loan interest costs.

• Quality and Efficiency:
  Better insulation and airtightness from kit builds translate into long-term energy savings that traditional builds may struggle to match without added costs. So you need to consider the lifetime savings on energy bills as part of the cost equation.

Segment 3: Hidden Cost Advantages of Kit Builds

• Reduced Risk of Weather Delays:
  Since much of the building occurs off-site, kit builds are less susceptible to weather-related delays that add time and cost to traditional projects.
• Waste and Disposal:
  Less onsite waste means fewer disposal fees and a smaller environmental footprint. Typically, you would need 3 skips with a traditional build, to take away the soil from the foundation excavation then all the material offcuts and surplus materials such as ready mixed concrete. With a kit build you would only need one skip, so there would be a cost saving as well as an environmental saving.
• Predictability:
  Costs tend to be more transparent and less prone to unexpected overruns with kit builds compared to traditional builds, where delay and hidden issues often balloon budgets. This is an important  consideration because I know from personal experience I can control the build with a kit extension far better than a traditional build so you are much more likely to have a build with no extra costs due to unforeseen problems.

Ultimately, kit builds offer homeowners a compelling financial advantage—not necessarily because the initial  price is lower as this isn’t always the case, but because the total cost of ownership, including speed, quality, and energy savings, often outperforms traditional methods.

If you are planning an extension, consider these true cost benefits carefully when choosing your build approach.

 “Whether you’re a homeowner, builder, architect or developer if you’re ready to explore SIPs seriously — you’re in the right place.

Subscribe to this podcast, leave a review, and share it.

Or more information go to: kitbuilds.org.uk

Until the next time.

Build smarter. Build faster. Build for the future.

This is KitBuilds.org.uk, I’m Paul Bird. Thanks for listening.