Timber frame extensions are being used more and more. This is due to how quickly they can be built, their energy efficiency and the wide array of designs possible.
If you’re considering a timber frame extension or building, you may be wondering how much you should expect to pay.
This article will cover the costs involved, the sorts of factors that can alter these prices and common questions people have surrounding the use of timber frame for an extension.
Timber Frame Cost per m²
A structural timber frame can be priced at £150/m² of the gross internal floor area.
Included within this timber frame cost is vertical studs with plywood sheathing to form internal and external walls, horizontal joists and sheathing to form upper floors and roofing and roof trusses.
This rate is for the south-east or southern London area. Price adjustments based on location are detailed within the factors section.
Timber Frame Extension Cost per m²
Below are the average costings of all the elements needed to create a timber frame extension:
|Element||Work Included in Element||Cost|
|Substructures||Strip Foundations, Blockwork / Engineered Brick Cavity Walls, DPC, Concrete Slab, hardcore, blinding, DPM, insulation, screed||£110/m²|
|Frame||Timber Frame Structure - including stud walls, roof trusses, upper floor structure||£150/m²|
|Roof||Roof coverings including battens, membranes, insulation, felt, tiles, soffit, fascia & rainwater goods||£124/m²|
|External Walls||SIPS (studs in frame) - including insulation, OSB board, membranes, plasterboard. Chimneys||£119/m²|
|Windows and External Doors||uPVC windows / doors||£114/m²|
|Internal Walls & Partitions||Plasterboard and insulation (studs in frame)||£60/m²|
|Internal Doors||Softwood internal doorsets, ironmongery and decoration||£67/m²|
|Wall Finishes||Paint, wall tiling, skim etc||£36/m²|
|Floor Finishes||Carpet, tiling, hardwood flooring, skirtings etc||£46/m²|
|Ceiling Finishes||Plasterboard and skim||£28/m²|
|Furniture, Fixtures, and Equipment||Stove, Kitchens, Bathrooms, Wardrobes, shelving etc||£115/m²|
|Mechanical||Heating & Plumbing||£75/m²|
|Electrical||Electrics & Lighting||£82/m²|
|External Works||Storm & foul drainage, water & sewage connections||£55/m²|
|Design Team & Survey Fees||£120/m²|
|Prelims||Scaffolding, welfare, warranties and site attendances||£120/m²|
Therefore, for an average single-storey timber frame extension of 4m x 5m, £28,880 would be a good price to budget for.
Factors Affecting the Cost of TImer Frame Extensions
Number of Storeys
When timber frames are used for structures higher than two storeys this can often increase cost per m². This is because of more structural timber required at lower levels to support the structure.
Specification of the System Selected
This includes elements like the size of timbers, type of plywood and the thickness of plywood. All vary in price and can cause cost differences.
Weight of the Structure
If heavy loads need to be supported heavy loads, more timber is needed to adequately support the structure, thus increasing cost.
Level of Design Required Prior to Construction
In particularly complex timber frame structures more time can be spent by a designer / structural engineer on drawings and design, thus increasing the system cost.
The above rates are for the South East/Outer London Area. You can use the following adjustments depending on where you live. These are based on the BCIS and Spon indices.
|South East (Southampton, Oxford, Kent, Outer London)||0|
|South West (Bristol, Exeter)||-4%|
|West Midlands (Birmingham)||-10%|
|East Midlands (Northampton, Nottingham, Leicester)||-10%|
|East Anglia (Cambridge, Norwich, Ipswich)||-5%|
|North West (Liverpool, Manchester)||-12%|
|Yorkshire and Humberside (Leeds, Sheffield)||-11%|
|North East (Newcastle, Sunderland)||-10%|
|Scotland (Edinburgh, Glasgow)||-6%|
|Wales (Cardiff, Swansea)||-9%|
|Northern Ireland (Belfast)||-12%|
Are Timber Frame Extensions Worth It?
Timber frame extensions quite literally have timber frames as opposed to being constructed from brick and mortar. There is nothing peculiar about this – some 25% to 30% of new-build UK homes are built with timber frames.
The overall benefits of a timber frame extension are largely the same as a brick extension, but there are a few nuances and caveats. Generally, you can expect at least the same increase in value as you would from a brick extension, though, if not more if the resulting extension boasts excellent energy efficiency.
A well-crafted timber frame extension that embraces its natural aesthetics can look beautiful and they’re very trendy right now due to their sustainable and environmentally-friendly credentials.
You don’t need a timber frame house to build a timber frame extension either, they’re 100% compatible.
The ONS offers a tool for checking how much an extension can add to the value of a home. The less space there is locally and the higher the home’s initial value is, the more value an extension will add to your home.
Are Timber Frame Extensions Sustainable?
So long as the timber is sustainably sourced, it is arguably a 100% sustainable resource. Timber frame houses can actually save some 4 tonnes of CO2 per build compared to brick and masonry.
Brick and mortar have to be mined, transported and synthesised with additives, a process that requires considerable energy, whereas timber regrows and is sustainable if managed properly. Timber also acts as a carbon store and possesses excellent insulative qualities compared to brick.
As such, timber frame extensions have eco-friendly and green credentials that are further increasing their popularity throughout the UK.
“The insulation is pre-fitted into the structural panels, which have been designed to deliver excellent thermal and airtightness properties,” – Simon Orrells, MD at Frame Technologies.
Pros and Cons of Timber Frame Extensions
Timber frame extensions achieve a similar end product to a traditional house extension, with some unique nuances and caveats. Here are the pros and cons of timber frame extensions:
Pros of Timber Frame Extensions
Timber frame extensions are often slightly cheaper than traditional extensions, though the difference may be marginal. This really depends on the complexity and size of the design. Even so, a 5% to 10% reduction in costs is still massive and that extra money can be contributed to other aspects of the project.
Timber frames are much quicker and easier to erect. There’s no need to build a brick wall – the timber frame is simply erected in-situ. Some modular systems are built off-site and simply transported to the site in a ready-made state, leaving very little work to be done. The project timeline is generally predictable, even in the winter months.
Wood is a better insulator than brick and rock and is easier to heat. Timber frame constructions pair exceptionally well with cheap-to-run, eco-friendly underfloor heating.
Wood is also exceptionally good at absorbing sound and is well sound-proofed from exterior noise.
Design and Aesthetics
Timber frame extensions can be built to resemble the rest of the house in the same way as a traditional extension. Many choose to embrace the natural wooden aesthetic and build timber frame extensions as a somewhat separate building, annex or outhouse.
Drawbacks of Timber Frame Extensions
Timber frame extensions are not necessarily harder to build than brick extensions, but the architect contractors absolutely need to be specialists in the field. Resultantly, there is less leeway when it comes to costing a timber frame extension as they have to be of a certain standard to be safe and compliant.
Rot and Infestation
A well-made timber frame extension is not at risk of rot or infestation, but again, this relies on quality architects and contractors who follow correct building regulations and protocol.
Planning Permission for Timber Frame Extensions
Timber frame extensions fall under the same rules as standard extensions. In some situations, they fall under Permitted Development and will not require Planning Permission, so long as they fulfil certain criteria.
Note, the following criteria may not apply in the following areas:
- Areas of Outstanding Natural Beauty
- Conservation Areas
- Listed buildings
- National Parks
- World Heritage Sites
Permitted Development only applies to the ‘original fabric of the building’. Homes that have already been extended won’t count as the ‘original fabric’. Essentially, you can’t extend an already-extended house using PDRs.
To come under PDRs and not require Planning Permission, for all timber frame extensions:
- Can’t alter the original roof
- The extension cannot be higher than the original roof or higher than 3m within 2m of a boundary
- Must not extend beyond the front of the house
- Only half the property land can be covered by extensions
For side timber frame extensions:
- Cannot exceed 4m
- Only up to half with the width of the original house
- Single storey only
For single-storey timber frame extensions:
- Cannot extend beyond the rear wall by more than 4m for detached or 3m otherwise
For time frame extensions with more than one storey:
- Must not extend beyond the rear wall by more than 3m
- Roof pitch must match the original roof
Following a consultation scheme with neighbours (which is not the same as Planning Permission), It’s possible to extend by:
- Over 4m and up to 8 metres for detached houses
- Over 3m and up to 6 metres for other houses
Contact your local Planning Authority before commencing with your project. It’s highly recommended that you obtain a Lawful Development Certificate and most contractors (if not all) will require this.
Generally, the timber frame extension must be built from fire-resistant treated timber and fire-resistant linings must be built-in to the ceiling and walls.
Additionally, if the timber frame extension walls are built on a boundary then the external finish needs to be built from a non-combustible material and must provide at least one hour’s fire resistance.
Your architect will advise on complying with Building Regulations for your own specific timber frame project.
Different Types of Timber Frame Extension
There are a few different types of timber frame construction methods. Your architect will advise on the best approach.
Platform Frame Method
The platform frame method is only typically relevant if building multi-storey timber frame extensions and buildings. The method can actually support buildings of some seven stories.
Floor structures are placed on wall panels that bear the primary load – the platform bears the weight of the vertical timber frame.
Probably the simplest method and the most popular method used for straightforward one-story extensions. Involves the erection of a timber frame upon which a non-load-bearing ceiling or weight-bearing floors are built.
Volumetric or Modular
Modular timber frame extensions are built off-site. The semi-finished product is then lifted into place in its entirety. This option is becoming increasingly popular as it allows the bulk of the extension to be built off-site in a controlled, professionally-equipped environment. Modular designs also save waste and involve minimal on-site disruption.
Walls For Timber Frame Extensions
Timber frame extensions do not need to look like they’re built from timber at all if that is not the desired effect.
The timber frame extension can actually be finished with a variety of different external walls, including:
- Fibre cement cladding
- Metal cladding
- Natural stone
- Render board
- Rendered brickwork
Many choose to style the timber frame extension differently to the house, forming its own enclosed exterior space, annex or outhouse. Others like it to look continuous with the house, as is typical with classic brick extensions.
How Do Timber Frame Extensions Work?
Timber frame extensions contain a number of components, including:
- External cladding materials, e.g. brick, which styles the outside of the building, also providing weather resistance.
- Breather membranes to ensure that the frame resists moisture penetration from outside, whilst allowing for some flexibility.
- Wooden lining fitted inside the frame to provide rigidity.
- Insulation fitted between panels.
- Vapour control layer (VCL), which aids in controlling condensation.
- The void or service zone for wiring electrics, plumbing, etc.
- Where applicable, second-storey flooring or pitched roofs fitted with insulation and tiled.
They’re built using either open or closed panel systems.
- Open panel systems are constructed using an open frame which can be customised on-site and fitted with windows, doors, insulation, etc. These require more work on-site but provide more flexibility.
- Closed panel systems are manufactured off-site and are built with insulation and other layers integrated already. These are ideal for modular constructions and leave less work on-site.
Get Prices on Timber Frame Extensions Near You
Timber extensions are still relatively new in the UK market. This means finding professional builders specialising in timber frames can be difficult.
We work with all the best timber frame extension builders ready to price your job. Get free, no-obligation quotes in your local area and compare prices using the form below.
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