Today the upper floors in most new homes are built using factory- made timber I-joists (also known as I-beams). These are basically timber RSJs (rolled steel joists) with an I-shaped cross-section comprising top and bottom flanges made of softwood or LVT (laminated veneer timber) bonded to a tall vertical web of OSB (oriented strand board), or a similar engineered board. Their main appeal is that, being strong and lightweight, they can span 6m or more, without support from internal walls or beams.
While they cost roughly twice as much as standard softwood joists, they be installed in half the time. Their superior rigidity and strength-to-weight ratio makes for easier handling, and they typically feature pre-formed knock-out panels designed for pipes and cables to be threaded through. They can be cut to length and the webs can be drilled, but the top and bottom flanges must not be cut. To provide lateral support, ‘blocking panels’ made from strips of engineered wood or spare I-joist o cuts are wedged between the joist ends.
There’s another reason why I-joists have captured the hearts of developers, self-builders and renovators alike — unlike standard softwood joists, I-joists aren’t prone to shrinking and warping, making them perfect for ‘quiet floors’. It’s even claimed that some products do not require sound insulation when installed at 400mm centres or closer.
I-joists: A Good Alternative to Softwood Joists
Timber I-joists are a popular alternative to softwood joists due to their stability (they’re not prone to warping, so provide a ‘quiet floor’) and ability to span greater widths. The webs can be drilled to accommodate services, but can also be specied with pre-formed knock-out holes for this purpose.
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