Structural Systems: Timber Frame

The timber frame is an extremely prevalent choice for self builders. Many love the fact that onsite time is kept to a minimum, others adore the idea of using a natural material that’s relatively simple to construct with. Timer frame is one of the most flexible methods of construction available and can be used to create almost any style of building, from a contemporary barn to a country cottage and everything in between.

A major benefit for self builders is the fact that flexibility and simplicity come together in one package. Design choices are tactile thanks to the wide range of engineered timber products that architects and manufacturers can draw upon. The simplicity comes from the fact that the entire structural envelope will be supplied by on business in a coherent, co-ordinated package.

The basics

In modern terms, timber frame refers to a panelized building method where large wall sections are produced in a factory and delivered to site in a kit form, ready for construction. The manufacturing conditions mean that all details are extremely accurate, with little or no margin for error.

There are two main forms of this system to consider: open or closed panels. The essential elements of both are softwood studs with rigid boards (such as plywood or OSB) that provide bracing. The name ‘open panel’ derives from the fact that the wall elements arrive on site with one side unbounded. They are left unfinished until the building is featherlight, at which point service runs and the insulation are fixed. The open side is closed off with a sheet of plaster or a gypsum-fibre board, such as Fermacell, with a vapor control layer inside.

Closed panels are similar to open versions but have boards pre-fitted to both sides, encasing a layer of factory-installed insulation. They can be built with services, doors and windows already incorporated, too, should you so require. These panels do cost more than an open set up, but you’ll enjoy the associated benefits of a stress-free and rapid build process.

A timber frame home’s load bearing superstructure means there’s usually no need for the internal walls to carry any of the building’s weight. This gives you the freedom to choose between open plan or partitioned internal layouts - and you can reconfigure them cost-effectively if you requirements change in the future, too. However making amendments to the design during the construction stage isn’t always easy.

It helps everyone if all amendments are made during the design process. Living in the real world, this isn’t always possible and sometimes certain things only become obvious one the building is finally on site and the frame is being erected. Even at this late stage, changes are possible. How much they cost will depend on specific details, for example, it’s far easier to reposition a non load-bearing wall than it is to construct a new opening in a heavily loaded external wall.

Timings

A basic timber frame package will include the wall panels, ground and first floor structures and trussed roof. Typically, this will be offered as a supply and erect  kit, so the Fram will be raised by the manufacturer’s build team (or a recommended contractor). If you don’t want to take over the work at this stage, opt for a package company who can take your further, right up to completion if you so desire.

A conventional frame (basic package)  takes about 12 weeks to produce. It could take less than a week to physically manufacture all the components needed to construct a new home, and even the biggest project should take less than tree weeks to erect on site. Most take between one and two weeks. It is important to remember that before we can start manufacturing we have to agree the design with the customer, secure planning permission, prepare structural calculation, make a Building Regulations application and complete the detailed design ready for our factory, these are the bits that take time

Sustainability

When self builders specify their new home, a key requirement is often that dwelling be efficient to run, And this is something that’s easy to achieve with timber frame. It’s no coincidence that more Passivhaus buildings are constructed using timber-based methods than any other form of construction. Most timber frame houses will be built with an external wall that has a U-value between 0.22 and 0.15 W/m2K although many, particularly energy efficient home, may well be lower, I always tell our customer not to focus excessively on the U-value of the external wall as many factors act in combination to determine the thermal performance of the building envelope and  overall energy efficiency. Work with your frame company to develop a solution for new home that works for your lifestyle and your pocket, as well as keeping the various parameters in balance with each other. There is little point in constructing a dwelling with a building envelope consisting entirely of low U-value elements and then paying no attention to air tightness or thermal bridging - at bets it’s wateful and at worst you’ll be building in problems for the future.

Twin frame options  (such Wise Wall T from Frame Wise) are relatively new developments, created with the intention of combatting problems associated with air tightness and heat loss. These systems are based on utilising two skins of standard timber stud walling to allow a deeper timber frame that can be filled with a greater quantity of insulation. This ensures that no thermal bridging occurs within the construction, helping to maximize insulation performance.

A final thought on sustainability is that timber is a natural and renewable resource. Always check that the wood you procure has been sourced from a responsibly-managed forest  to ensure the very best eco credentials and chain of custody accreditation.