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Joist Choice
Winter 2006
Published:  10 December, 2006

MiTek’s Posi-Joist system

Engineered flooring systems are proving their worth in property developments where speed, reliability, strength and flexibility are all important factors. David Castle reports

As the pressure on land continues, many property developers are looking to squeeze as much accommodation into the smallest area possible.

A quick look at the developments in most towns and cities is enough to convince that, when it comes to modern living, flats and apartments are increasingly de rigueur.

It's no surprise, then, that apartment buildings now account for 41% of all housing completions in the UK, while Ireland is experiencing a similar trend. This has required a move away from traditional building methods, with the result that engineered flooring is now the fastest growing sector of the engineered wood products market.

Wolf Systems' easi-joist system, for example, is now employed by 37% of the company’s manufacturing customers – a huge increase on previous years.

Wolf Systems' easi-joist system
In essence, easi-joists are parallel cord trusses using stress graded timber cords. These cords are plated together with a procession engineered structural component called the metal web. Pressing the metal webs into the cords forms the easi-joist: in a complete floor situation, this becomes the easi-joist system. Open-web systems like easi-joist, and MiTek's Posi-Joist, which is a combination of a high strength steel web and strength-graded TR26 structural softwood cords, allow a high degree of speed and flexibility in the floor installation, and can span far greater distances than is possible with conventional timber products.

The original – and most popular – use for these systems is as floor joists, although they can also be used in cassette form, something that is becoming increasingly popular, as more and more prefabrication of components is being used in construction.

One of the other benefits of open-web systems is that they provide easy access for service runs, like plumbing and electricity cabling, reducing labour costs and build-time on site.

“Most houses have en suite bathrooms, some have two and houses with three floors have a bathroom on every level,” explained MiTek's sales and marketing director Roy Troman.

“In the past, notches and holes would have been drilled to make room for pipes. Nowadays, with engineered flooring systems, architects have a choice – if they don't want the en suite to back onto the bathroom, they don't have to. It's a massive advantage.”

Both systems can be used not only for floor joists, but can adequately span for flat and pitched roofs.

Finnforest’s SoundBar system comprises the Finnjoist, the SoundBar board and a screed
Troman said sales of Posi-Joist have doubled in the past year. “A lot of our sales are with timber frame manufacturers who have really pioneered the use of Posi-Joist. Another reason why they like it is that it's very quick to install: it's inherently stable, and can be incorporated into cassette floors. It's also extremely light and strong.”

Earlier this year, MiTek become the first metal-web manufacturer to be granted Robust Standard Detail (E-FT-4) for a metal-web joist, following months of exhausting tests at four separate developments.

Other companies are also taking engineered floor systems seriously. Finnforest has launched its SoundBar System, a flooring system that promises not only to improve acoustic performance but, says the company, has the potential to reduce build times, deliver substantial cost savings, simplify site logistics and enhance the overall sales appeal of the finished building.

SoundBar comprises three components: the FinnJoist, the company's own I-joist; the SoundBar board, which sits above the normal floor deck, helping to deliver the system's acoustic performance; and an anydrite Gyvlon screed from LaFarge, which is pumpable and quick drying, with a smooth, self-levelling finish to complete the system.

The SoundBar system has already been tested at a Bellway Homes site in Purfleet, where 15 apartments with a floor area of 1,500m2 were installed using the system.

Kevin Riley, head of building solutions for Finnforest UK, said the system “addresses the government's rethink about how we build our homes.

“A flooring system of this type with these benefits has never been conceived using wooden joist before,” he added.