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Extending your home is one of the biggest building projects most people take on, and the frame you choose shapes your budget, your timescale and how comfortable the finished room feels for years afterwards. A timber frame extension kit, designed around your own drawings and precision-manufactured in a controlled workshop environment, can reduce construction time on site, improve energy efficiency and integrate cleanly with your existing house. At Cornish Frame Company, we design, produce and supply bespoke timber frame extension kits from our workshop in mid Cornwall, drawing on over 30 years of experience in timber frame construction across Cornwall and the South West.
For many homeowners, home extensions offer better long-term value than moving house, and a well-specified timber frame extension can make that extra space quicker and less disruptive to build. Whether you are planning a single-storey kitchen extension or a larger two-storey addition, we work from your architect's drawings to create a kit that fits your original house. |
What is a Timber Frame Extension Kit
A timber frame extension kit is a complete structural system, made to your project's own drawings rather than picked from a standard catalogue. Every panel, wall, and roof element is built to the exact dimensions of your extension, so it fits your existing structure without unnecessary cutting or adjustment upon arrival.
Unlike a generic frame extension package, a bespoke kit accounts for your plot's specific width, height and the junction points where the new structure meets the original house. This matters most where an extension needs a traditional appearance, such as period properties or homes within a conservation area.
We fabricate every kit in our workshop, then deliver the completed panels to your site ready for assembly. You can choose a manufacturer-only service if you already have a builder in place, or ask us to manage installation as part of a fuller, combined package.
Unlike a generic frame extension package, a bespoke kit accounts for your plot's specific width, height and the junction points where the new structure meets the original house. This matters most where an extension needs a traditional appearance, such as period properties or homes within a conservation area.
We fabricate every kit in our workshop, then deliver the completed panels to your site ready for assembly. You can choose a manufacturer-only service if you already have a builder in place, or ask us to manage installation as part of a fuller, combined package.
What is a Timber Frame Extension KitEvery extension kit is built around a small set of essential components, specified to suit your project rather than supplied as a fixed, off-the-shelf list. The table below sets out what a typical kit includes. We'll confirm exactly what applies to your extension once we've seen your design.
Structural timber frame panels Precision-manufactured wall and floor panels engineered to your extension's drawings and structural calculations Insulated frame panel build-up Timber walls specified to meet or exceed current energy efficiency requirements, with insulation thickness matched to your design Roof structure Flat or pitched roof structural elements, designed to suit your extension and tie cleanly into your existing house External cladding options A choice of finishes including timber cladding, such as cedar, metal cladding, or render to match your original house Structural drawings and calculations Full design detail covering structural elements, wind loading and the connections needed for structural safety Delivery Panels delivered ready for assembly, reducing handling, storage and waste on a live build Installation support Fitting guidance for your own contractors, or full installation carried out by our team from start to finish |
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Who Should Consider a Timber Frame Extension KitAn extension kit isn't the right fit for every project, but it suits certain builds particularly well. If speed, accuracy and a predictable programme matter to you as much as the finished look, here are the types of builds where this approach tends to work best:
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Benefits of a Timber Frame Extension
Choosing timber frame affects far more than how quickly your extension comes together — it shapes the comfort, sustainability, and long-term value of your finished space. Below are the key benefits homeowners gain by choosing this method for their extension.
Faster Build Times
Your kit is produced before it reaches the site, which reduces construction time significantly compared with traditional brick and block.
Not Weather Dependent
Assembling a timber-frame extension doesn't rely on the same conditions as traditional brickwork, helping keep your programme on track through a Cornish winter.
Strong Thermal Performance
Timber frame panels can achieve high levels of insulation while remaining thinner than an equivalent brick wall.
Lower Embodied Carbon
Timber is a renewable material with a lower embodied footprint than steel or concrete, and sustainably sourced timber acts as a natural carbon sink.
Lightweight Construction
Timber is lighter than concrete or brick, reducing stress on your existing structure and its foundations.
Good Dimensional Accuracy
Every panel is crafted to your drawings under controlled workshop conditions rather than built up on an open plot.
Less Disruption to Daily Life at Home
You get a shorter, more predictable build programme and less mess than an extension built entirely by traditional methods.
Blends With Your Home
Cladding and finish options let a new extension sit comfortably alongside your original house.
Faster Build Times
Your kit is produced before it reaches the site, which reduces construction time significantly compared with traditional brick and block.
Not Weather Dependent
Assembling a timber-frame extension doesn't rely on the same conditions as traditional brickwork, helping keep your programme on track through a Cornish winter.
Strong Thermal Performance
Timber frame panels can achieve high levels of insulation while remaining thinner than an equivalent brick wall.
Lower Embodied Carbon
Timber is a renewable material with a lower embodied footprint than steel or concrete, and sustainably sourced timber acts as a natural carbon sink.
Lightweight Construction
Timber is lighter than concrete or brick, reducing stress on your existing structure and its foundations.
Good Dimensional Accuracy
Every panel is crafted to your drawings under controlled workshop conditions rather than built up on an open plot.
Less Disruption to Daily Life at Home
You get a shorter, more predictable build programme and less mess than an extension built entirely by traditional methods.
Blends With Your Home
Cladding and finish options let a new extension sit comfortably alongside your original house.
Get a Quote for Your Timber Frame Extension KitIf you have drawings, even early ones, we can give you an honest indication of cost and timescale for your extension. Send us your plans by email, phone or our enquiry form, and we'll talk you through your options.
Get a quote |
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Our Process: From Drawings to InstallationOur process is designed to keep you informed and reassured at every stage. We stay involved at each step and remain on hand after your build is complete, so you always know what's happening next and who to call if any questions arise.
Initial Conversation and Site Visit We meet with you to discuss your plans, assess delivery access, and talk through what's achievable within your budget. Design and Structural Drawings Our design team produces drawings covering wall build-up, insulation specification, roof structure, and ventilation requirements. Planning Permission and Regulatory Checks We help you understand whether your project falls under permitted development or needs formal planning permission. Precision Manufacture Your kit is constructed in our mid-Cornwall workshop to the exact specification agreed at the design stage, with quality checked at every stage. Delivery Your completed panels arrive ready for assembly at a time that fits your build programme. Installation We offer either a manufacture-only kit for your own contractors or full installation carried out by our team, connecting your new frame extension to the existing structure. Ongoing Support You have someone to call throughout your build if a question comes up about your frame or its performance. |
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What Affects Timber Frame Extension Cost
Every timber frame extension is priced differently, which makes it hard to pin down a figure before you've had a proper conversation about your project. Rather than leave you guessing, here's a clear breakdown of the factors that genuinely move the price up or down, so you can see where your budget is going and where you have room to make choices.
Size of the extension
Larger extensions, measured in square metres, require more materials and structural elements, which increase overall cost.
Single-storey or two-storey
A single-storey extension is typically less complex and more cost-effective than a two-storey addition.
Design complexity
Junctions with the existing structure, unusual shapes or a flat roof design can add to design complexity and cost.
Timber type
The timber type specified for your frame and cladding affects material cost and the finished appearance.
Exterior finish
The choice of cladding—timber, metal, or a rendered finish—significantly influences the total cost.
Insulation specification
Higher levels of insulation improve long-term thermal performance but affect frame structure thickness, materials and cost.
Kit only or full install
A kit supplied on its own costs less than a combined design-and-installation package.
There is no single figure that applies to every timber frame extension cost, because so much depends on your project's size, design complexity and chosen finish. We'll talk through what affects the price of your extension kit early on, so you have a clear, honest figure to plan around before any manufacturing begins.
Size of the extension
Larger extensions, measured in square metres, require more materials and structural elements, which increase overall cost.
Single-storey or two-storey
A single-storey extension is typically less complex and more cost-effective than a two-storey addition.
Design complexity
Junctions with the existing structure, unusual shapes or a flat roof design can add to design complexity and cost.
Timber type
The timber type specified for your frame and cladding affects material cost and the finished appearance.
Exterior finish
The choice of cladding—timber, metal, or a rendered finish—significantly influences the total cost.
Insulation specification
Higher levels of insulation improve long-term thermal performance but affect frame structure thickness, materials and cost.
Kit only or full install
A kit supplied on its own costs less than a combined design-and-installation package.
There is no single figure that applies to every timber frame extension cost, because so much depends on your project's size, design complexity and chosen finish. We'll talk through what affects the price of your extension kit early on, so you have a clear, honest figure to plan around before any manufacturing begins.
Areas we deliver to
Our timber frame kits are manufactured in Cornwall and delivered across the country.
We regularly deliver to:
We regularly deliver to:
- South West: Cornwall, Devon, Somerset, Dorset, and Wiltshire
- South East: Hampshire, Sussex, Surrey, Kent, and Berkshire
- Wales: South Wales and the West Wales coastline
- Midlands and North: project-dependent, please get in touch for delivery costs
Planning Permission, Building Regulations and Fire Safety
Many single-storey extensions fall within permitted development, meaning formal planning permission may not always be required, though this depends on your property, its size and its location. Extensions built without the necessary permission where required can lead to enforcement action, so it's worth confirming your position with your local planning authority before work begins, particularly if your property is within a conservation area.
Building regulations apply separately from planning permission, and they exist to ensure structural safety throughout your extension. This also covers matters such as escape routes and the resistance of walls close to a boundary. We design every timber frame extension kit with these requirements in mind, and we're happy to talk you through what applies to your specific project.
For general guidance, you can also refer to the Planning Portal's guidance on permitted development for extensions and the government's collection of approved documents on energy performance.
Building regulations apply separately from planning permission, and they exist to ensure structural safety throughout your extension. This also covers matters such as escape routes and the resistance of walls close to a boundary. We design every timber frame extension kit with these requirements in mind, and we're happy to talk you through what applies to your specific project.
For general guidance, you can also refer to the Planning Portal's guidance on permitted development for extensions and the government's collection of approved documents on energy performance.
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faq'sWhat is included in a timber frame extension kit?
A typical kit includes manufactured wall and roof panels built to your drawings, structural calculations, an insulated wall build-up specified to suit your project, and your choice of external cladding. We can supply the kit on its own for your own contractors, or combine it with a full installation. Get in touch to discuss your project. How much does a timber frame extension cost?
Cost varies with the size of your extension, its design, the timber type and finish you choose, and whether you want fabrication only or a full installation package. We give every customer an honest, itemised figure once we understand your drawings, rather than a generic price that doesn't reflect your project. Do I need planning permission for a timber frame extension?
It depends on your property and the size and position of the extension. Many single-storey extensions fall within permitted development, but larger extensions, those close to a boundary, or properties in a conservation area often need formal planning permission. We recommend checking with your local planning authority, and we're happy to talk through what's likely to apply to your project. How do timber frame extensions meet building regulations?
Every kit we design and produce is built to comply with current UK building regulations, covering structural safety, insulation and energy efficiency. Our structural drawings and calculations form part of the regulatory application for your extension. How long does it take to manufacture and install a single-storey extension kit?
Production time depends on the size and complexity of your extension, and we'll provide a realistic timescale once we review your drawings. Because the frame is manufactured in a controlled workshop, on-site assembly is usually much quicker than traditional blockwork. It isn't held up by poor weather. Is a timber frame extension cost-effective compared to traditional building work?
For most extensions, yes. A kit crafted accurately to your drawings reduces the labour and time needed on site, which can make a timber frame extension more cost-effective overall than an extension built entirely from brick and block, even where material costs are similar. How do you handle fire safety in a frame extension?
Fire safety is designed in from the start, in line with current building regulations. This covers the resistance of walls close to a boundary, appropriate escape routes, and correct detailing at every junction with your existing structure. If you have specific concerns about your plans, we'll address them as part of your design. |
