When engineered timber I-joists arrived in the UK their low weight and extra long lengths were welcomed by building contractors who relished their portability and accommodation of long spans.
However, it is not only ease of handling that is winning these products support. For housebuilders there are design benefits to be gained from replacing traditional timber joists with an engineered timber equivalent.
Take soil pipes, for example. Typically, these run from the ground floor to the roof. Traditional timber joists need a hole to be cut to accommodate the soil pipe, which normally means extra work to trim the joists around the pipe, and the choice of soil pipe position is often limited. With TJI joists, designers can arrange for the pipe to pass within the floor zone, as the geometrical properties of the joists allow the pipe to be ‘fed through’ their web. This facilitates greater positioning flexibility which can enable designers to build more economy into their designs.
It is important that soil pipes, ducted floor heating and other large services are built into the design itself, rather than attempting to retro-fit. TJI joists have pre-punched knock-out holes to make the process still easier.
Another design detail to consider is that of multiple joists. Traditional timber joists are often not available in longer lengths so when larger members are required it is often necessary to bolt a series of joists together. These configurations are time-consuming and awkward. TJI joists go up to 15m and even 20m if required.
Using engineered timber joists around stairwells can also save time and money. For a typical house stairwell, fewer engineered timber components are required than their solid timber equivalents, providing more rapid installation. Moreover, TJI joists can be cantilevered up to 30% of the adjacent span if not supporting concentrated loads on the cantilever.
The joists’ capacity to cut movement and distortion in flooring also ensures squeak-free stairs.
