Timber frame is a popular construction system for those looking for a fast build time on site and factory standards. No longer a niche within the self build market, according to a 2017 report*, the number of projects built with timber frame (and SIPs) is almost equal to the number of projects built with masonry.
What is Timber Frame?
At its most basic, a timber frame structure features walls consisting 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 on the outside with a waterproof barrier and then wrapped around this are the external wall elements, which can be either built up out of the ground (brick or stone), or hung off the timber frame walls — as would happen with timber cladding or tiles.
In terms of buildability, timber frame tends to work best with simpler-shaped structures and it really comes into its own when combined with lightweight wall claddings such as timber, tiles or render on boarding. This can reduce wall widths by up to 150mm, which adds a surprising amount to internal floor areas.
(MORE: Step-by-step guide to building a timber frame post and beam home)
Choosing a Timber Frame System
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.
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 already 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 timber frame panels may be delivered to site ‘open’ or ‘closed’.
Do SIPs Count as Timber Frame?
SIPs construction is sometimes referred to as timber frame without the timber. The strength of the panels derives from bonding insulation within an inner and outer skin of board to make a very rigid, highly insulated shell.
The On Site Process
The factory produces these panels, leaving holes where the doors and windows will be placed later, and then ships them off to site where, together with flooring elements and roof trusses, the superstructure of the house is erected in a few days.
The roof is left with a waterproof covering and, once the frame erectors have finished, work can commence both inside and outside of the house.
It’s very speedy and you can work in the wet.
- Any construction below finished ground level would need to be built using masonry or concrete. However, the storeys above that level can be built using timber frame
- 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
How Much Does a Timber Frame Cost?
The frame, associated design work, delivery and assembly on site is charged as a package by timber frame companies, providing a level of cost certainty.
In terms of cost, open-panel systems remain the cheapest to produce, but as the requirements for lower U values and better airtightness levels increase, the cost differentials are being narrowed.
The SIPs and closed-panel options tend to cost around 10–15% more for the frame, but offer better performance and less site-time in compensation.
Bear in mind that the timber frame element of a house is rarely more than 30 percent of the overall budget, so the added costs may fall to as little as 3–5 percent on the overall build total — which is little different to what you might spend on a more luxurious kitchen or a whole-house lighting scheme.
Perhaps of more interest to self builders is how timber frame stacks up against traditional masonry builds. In terms of cost, there isn’t a clear winner. The cost of masonry builds tends to go up and down with market conditions — in contrast, timber frame prices tend to vary much less.
How to Find a Timber Frame Supplier
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. This makes for difficulties when making comparisons between companies.
Tips for Finding the Right Supplier
- Choose a member of the Structural Timber Association
- Ask three or four companies to provide a quote for your project. They will need your drawings (ideally plans/sections/elevations to a scale of no less than 1:100), along with as detailed a specification as you can
- 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. Don’t automatically reject the most expensive quotation — the company may have quoted for a higher specification or for more elements of the build
- Once you have narrowed your choice to two manufacturers, arrange to meet them at their factory, where you can go through their quote in detail
- Ask if they have any suggestions for saving costs, as fairly small changes to the plans can often mean large cost savings
- While you are at the factory, request a tour and see, touch and feel the various materials they plan to use. Ask about lead times, too. Expect a 10-12 week lead in time for the structural shell from when you place an order
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.
Why Choose Timber Frame?
- Timber frame lends itself to those who hope to take on the role of project manager, as the superstructure is built by a single company
- The frame is engineered in factory conditions meaning walls and floors are perfectly square
- This means there’s also less scope for ‘human error’ during the build
- Allows for rapid build speeds
- Finished 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