What is a timber frame extension?

Timber frames are built from wood and these types of extension can either be made on-site by a joiner or be pre-built in a warehouse or factory. Timber frame extensions are usually designed by a structural engineer, who determines the size and grading of the timbers required.

This design typically includes the frame, lintels, cripple studs and a nailing schedule. Initial design work is essential to ensure a fast build and a robust and long-lasting timber extension. Your exterior can be finished in any material you choose such as cladding, brickwork, glazing or rendering.

You can choose between a variety of build materials. These include closed sheet panel systems with factory fitted insulation, open panels ready for glazing to be fitted, or SIPs, which are Structural Insulated Panels.

Why choose a timber frame extension?

There are many benefits to opting for a timber frame rather than a traditional brick build:

  • Your extension is weathertight in days rather than weeks
  • Timber offers good thermal performance for energy efficiency
  • The materials used are more sustainable and eco-friendly
  • Fewer labour hours are required for the build, making it a cost-effective option
  • Timescales are more predictable, as the construction is less likely to stall in bad weather
  • Interior design is flexible, with an easy option for creating open plan living or constructing non-load bearing stud walls

Homeowners also opt for timber frames for the aesthetic this offers; a timber frame extension that is primarily finished in glazing is a contemporary, modern design that will flood your home with natural light.

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What are the uses for a timber frame extension?

As with any type of extension, you can choose a timber frame for a multitude of purposes. Complete new builds can be constructed for timber frames, or they can be used for:

  • Single storey extensions to any aspect of your home
  • Sunrooms, conservatories and summer houses
  • Office spaces
  • Relaxation and garden rooms
  • Extensions to existing rooms – such as extending your kitchen outwards
  • Double-height extensions

This flexibility is owing to the individual nature of the timber frame design – this is tailored to your home and your extension so you might choose a flat roof, gable roof, pitched roof and any number of finishes.

You can also mix and match the materials used in a timber frame extension. For example, you might opt for insulated timber panels with steel beams, or glulam, which is a laminated timber beam. This allows you to select the most cost-effective materials for your project.

How much does a timber frame extension cost?

The cost of building a timber frame extension depends on the size, design, materials and structure of your build. Typically a timber frame build will start at £1,800 per m2 and increase up to around £2,400 m2 for an oak frame.

If you decide to purchase a timber frame package, this usually includes:

  • Structural wall panels, both internal and external
  • The waterproof membrane
  • Floor joists and flooring covers – excluding the finished flooring material
  • Roof structure, generally prefabricated trusses
  • Soleplates, clips and the damp-proof courses

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What factors impact the cost of a timber frame extension?

With so many design and material choices, your initial budget and design specification will dictate the construction of your extension.

Cost considerations to think about include:

  1. How thick your frame needs to be
  2. What type and material of frame you choose
  3. How much insulation you need, and of what type
  4. Whether your extension is prefabricated, partially prefabricated, or built on-site
  5. What material(s) you choose to clad your extension in
  6. How much glazing you need, and whether this is custom sizing
  7. Where your site is located, the proximity to timber frame specialists and ease of site access

With so many variables, it is wise to take a look at other timber frame extensions for design inspiration and discuss the material choices best suited to your budget with your contractor.

How to choose the right timber frame extension?

Your extension design will depend on the location in relation to your property, the size of your conversion and its intended purpose.

Examples of the type of finishes you can choose from for the exterior appearance of your extension include:

  • Natural stone
  • Render boarding
  • Fibre cement cladding
  • Reconstituted stone
  • Rendered brickwork
  • Metal cladding
  • Timber
  • Glazing panels
  • Brick slips

For most extensions the type of finish you choose will depend on the existing appearance of your home, and either what design will best complement this or how much contrast you would like your new extension to have.

The cost of building a timber frame extension depends on the size, design, materials and structure of your build. Typically a timber frame build will start at £1,800 per m2 and increase up to around £2,400 m2 for an oak frame.

Frequently asked questions

Do I need planning permission for a timber frame extension?

Planning permission does not depend so much on what your extension is built from so much as the size, appearance and location of the build.

Many extensions are possible without planning permission under permitted development (PD) but this depends on how close your extension will come to property boundaries, whether the height, width or length will exceed that of your home, and how much of the land space you will be building on.

If in any doubt whether permitted development applies, contact your local planning authority for guidance before any work begins.

How long does it take to build a timber frame extension?

Timber frames can be constructed off-site or on-site, depending on the design. Softwood and sheet panel systems can be constructed on-site, or panels can be made in a workshop beforehand and then be assembled quickly on site.

Most timber frame extensions take between eight to twelve weeks to build; this is the lead-time you should factor in if your frame or panels are being made in a workshop. This means that the on-site construction process is very fast, and much quicker than the build time required to construct a brick extension.

The actual construction time takes days, rather than weeks. This is one of the primary benefits of choosing timber; the disruption is far reduced with an efficient and fast build. The majority of the time is required for the timbers, panels and beams to be crafted and cut to size. These are then delivered to site and pieced together.

How is a timber frame extension built?

Many timber frame shells are produced in a factory; more bespoke projects may need to be completed on-site by a joiner. This all depends on how much of the design is prefabricated and how much is being built to specification.

Many prefabricated panels are built using compute controlled manufacturing, so are highly accurate in measurements.

The core of a timber frame is the load-bearing walls, which are often made from lightweight engineered panels with studwork bonding wooden panels or sheathing, for example, oriented strand board (OSB).

Those gaps between the studs are then filled with insulation to create an energy-efficient and low heating cost panel, offering slimmer walls with higher energy ratings than brickwork to maximise the amount of floor space available.

What build costs are not included in a timber frame?

If you appoint a contractor to manage your extension build start to finish, they will likely engage several tradespeople to carry out the various tasks involved in the completed extension.

However, if you commission a timber frame specialist to construct the frame, it is important to understand what aspects of your extension are included within that cost, and what needs to be budgeted for separately.

Typically, the timber frame construction itself will not include:

  • Cladding or external finishes
  • Roofing – felt, roof tiles, battens
  • Insulation – depending on what sort of panels you choose, and whether these are prefabricated with insulation
  • Doors and glazing if your joinery is not pre-glazed
  • Decorating finishes including tiling, flooring and wall finishes
  • Electrics, heating and plumbing
  • Any fitted units for kitchens, bathrooms or storage

It is also important to understand where in the process your groundwork, landscaping and drainage will be completed, and whether this is included in the quote.

What is a movement gap in timber frame extensions?

A movement gap is an allowance made for any material shrinkage, movement according to moisture levels, and expansion or contraction due to heat. This applies to any natural materials such as wooden flooring, which can change in size in fluctuating temperatures.

Your extension will move at a different rate than your existing building since it has been built at a different time, and may be constructed from different materials. The movement gap is, therefore, a contingency to allow for those shrinkages and movements.

Movement joints are often built with stainless steel, created from a tie system to accommodate any movement, either vertically or horizontally, with a sealant used to ensure the movement gap is weatherproof.

Rich Crossley
Having spent 30 years working all over the world for top-tier investment banks, I’ve owned and developed houses all over the world – Europe, the US and Asia. I’m now based back in the UK and involved in the property industry – oh, and I’m a keen DIY enthusiast!
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