What is a Timber Frame?
Timber framed homes and extensions use panels built out of timber studwork.
At their most basic, timber frame walls consist of timber studwork fixed in place (typically) with OSB or plywood. The strength and rigidity is supplied by the board, which, when nailed to the studwork, makes a very rigid box known as an open panel – the panel is ‘closed’ once insulation has been introduced.
The frame is wrapped externally in a waterproof barrier before cladding is added.
Different Methods of Timber Framing
A timber framed home can be built on site; this method of construction is known as ‘stick build’. This method is often used for extensions, where it is difficult to get accurate manufacturing dimensions until the existing structure is exposed. (This method is common in the US, too.)
However, in the UK, timber frame homes are usually built in a factory and then rapidly assembled on site. Factory prefabrication is by far the most popular route chosen by self builders, as manufacturers have to work to strict quality control methods, ensuring the correct specification of materials are used and a high degree of dimensional accuracy is achieved
The panels may be delivered to site ‘open’ or ‘closed’ by your timber frame manufacturer.
Open vs. Closed Panels
Open panels are manufactured ready for external joinery (doors and windows) to be placed, and are delivered to site together with flooring elements and roof trusses. Once the frame erectors have finished, work can commence both inside and outside the house.
Closed panels are delivered to site with insulation factory fitted. The external cladding, windows and doors may be fixed, as may electrics and plumbing. (Alternatively, a service void may be added for self builders undecided on their electrical and plumbing scheme.)
Closed panels are often offered by German package build suppliers and can result in a very fast build. Due to the weight of the panels, a crane is essential to the assembly.
The Benefits of Timber Frame
Because the superstructure is taken care of by one company, timber frame lends itself to self builders who hope to take on the role of project manager. “Timber frame gives a single point of responsibility for the design and construction of the entire building superstructure — there’s no opportunity for blaming someone else when mistakes are made” says Paul Newman of Potton.
The timber frame will be engineered in factory conditions meaning walls and floors are square — an advantage when it comes to second fix work. The former means there’s also less scope for ‘human error’ during the build.
Timber frame panels are erected in a matter of days once on site, allowing for rapid build speeds.
Timber framed homes can achieve high U values with a comparatively slimmer wall profile.
A good number of timber frame suppliers are accustomed to working with self builders.
What to Consider
Timber framing is not suitable in all applications. Any construction below finished ground level, for example, would not use timber frame and would be built using masonry or concrete. However, there is no reason why the storeys above that level can’t be built using timber framing.
Ensuring the underbuilding is constructed to the correct dimensions and tolerances is key to ensuring that when the timber frame arrives on site to be erected, it fits.
Timber frame expert Mike Cruickshank – who’s spent 26 years with one of the UK’s leading timber frame manufacturers – addresses the common myths:
‘It’s more difficult to get a mortgage for timber frame’
None of the major lending institutions differentiate between modern timber frame construction and brick and block.
‘Timber frame homes have a limited lifespan’
In order to obtain a mortgage, the house has to have a minimum lifespan of 60 years, which timber frame provides.
‘Won’t a timber frame house rot?’
In order for timber to rot it has to have a moisture content in excess of 20% for a prolonged period, but with modern building methods, Building Regulations and a reasonable degree of property maintenance this should never be an issue.
‘Is a timber frame house going to be a fire risk?’
As with all construction types, Building Regs have to be fully complied with, which includes fire protection to the structural timber frame. The architect/designer will specify materials that reduce the potential for fire ignition, limit the spread of fire and stop the passage of hot gasses and smoke.
‘Do chartered surveyors put a lower valuation on timber frame houses?’ RICS does not apply a reduced valuation to a timber frame house; indeed there is a school of thought that because of their energy efficiency they should attract a premium.
Choosing a Company to Build Your Home
There are a good number of companies producing timber frames for the UK self build market.
The most common way to work is for the company to design, build and erect the superstructure but there are variations on how much of the superstructure is supplied. The service provided by timber frame companies can vary from the supply only of the superstructure to the complete package (i.e. a full turnkey housebuilding service). This makes for difficulties when making comparisons between companies.
When you are comparing manufacturers’ quotes, make sure that the two quotes have a comparable specification. Some manufacturers offer a free quote comparison service; if they do, it’s worth using it.
Using a timber frame manufacturer that is a member of the Structural Timber Association is a good idea. So is visiting the factory where your home is to be manufactured.
What’s Included in a Timber Frame Package
A basic package may typically consist of the following items:
- Soleplates, damp-proof courses and clips
- Structural external/internal wall panels and waterproof membrane
- Floor joists and floor covers (not finishes)
- All roof elements, usually supplied as prefabricated trusses
Items that are unlikely to be included unless the whole housebuilding contract is let to the timber frame company:
- External claddings
- Roofing materials: felt, batten, roof tiles, etc
- Floor screeds
- Chimney flues
- Glazing (though joinery is increasingly being supplied pre-glazed)
- Heating, plumbing and electrics
- Plaster finishes
- Kitchen units, fitted bedroom furniture and sanitaryware
- Decorating, wall and floor tiling and finishes
- Garage doors
- (Many package companies will not manage the groundworks, drainage and landscaping.)
You should look carefully at the specification offered by each company and check that you are comparing like with like.
The Cost of Timber Frame
The cost of the frame, associated design work, delivery and assembly on site is charged as a package by timber frame companies. On the plus side, this provides cost certainly
Source: Homebuilding and Renovating app