There’s joists and there’s joists. They all do the same job, but some are better at doing more than just holding the floor and walls up. There are also many brand names that can become confusing – but essentially there are only three types of joist.
There’s the trusty solid timber joists: used for centuries, perfect for the job but a little limited in strength and therefore the length they can span is also limited. However, they are very cost effective and perfect for almost all types of home unless you are planning on large spans or using lots of ventilation and wiring or plumbing demands the creation of lots of holes through the joists.
Then there’s the ‘I-joist’ – composite joist manufactured using laminated timber for the top and bottom components and OSB (Oriented Strand Board) or similar for the centre section which, when facing the end of the joist, forms the shape of a capital ‘I’ – hence the name. These were developed in the 1960’s so are nothing new and came about in answer to designers and architects who demanded longer spans than traditional solid timber joists could provide. They also allow larger holes to be created so that more services can be threaded through them.
The third option is a metal web joist. The top and bottom components are held together by a web of specially designed metal brackets. These have the same advantages of ‘I-joists’ but with the added benefit of being ‘open’ – so there’s no need to drill holes to run services through. They come into their own when installing ducting for heat recovery and ventilation systems and reduce the labour time it takes to install services, which ought to therefore represent a financial saving to you.