An engineered advantage

// the building envelope

Engineered wood products are being increasing specified in modern construction. HA asks Jon Stevenson, Marketing Manager of James Jones & Son, one of the largest timber processing groups in the UK, about the advantages of their best-selling product, the JJI-Joist.

What would be the main benefit to using JJI-Joists?

With over 55 million linear metres sold, JJI-Joists are the most widely specified engineered wood product in the UK and are used in residential and commercial construction as load-bearing and non load-bearing members for floors, walls and roofs.

They offer several advantages over traditional structural timber products including long lengths, a composition that resists shrinking and warping, an excellent strength to weight ratio, straight and uniform dimensions and, uniquely, are FSC® and PAS 2050 accredited.

What standard sizes and lengths do JJI-Joist come in? Can they be easily cut on site?

Manufactured in Scotland, JJI-Joists are available in a range of sizes familiar to the UK construction industry with joist depths ranging from 145mm to 450mm and with flanges ranging from 47mm to 97mm in width.  JJI-Joists are available in 8, 9, 10 & 12m standard lengths.
The solid timber flanges and OSB web make the JJI-Joist easier to work with on site. It is dimensionally stable, quick to install and simpler to work with. The flanges can be cut to length, nailed and screwed, and the OSB web makes cutting of holes straightforward for services including MVHR.

And what’s your sustainability record?

JJI-Joists are the only I-Joist available with either PEFC or FSC accreditation, and the manufacturing base in Forres is certified to ISO 14001 meaning we can meet the most demanding chain of custody requirements. Additionally, JJI-Joists are the only joist verified to PAS 2050, allowing architects, specifiers and builders to know the embodied carbon data for any JJI-Joist installation, important for calculating the carbon footprint of a project. More recently James Jones has become a member of the Industry recognised Supply Chain Sustainability School.

Is there any concern over fire risks?

James Jones and Sons have been heavily involved in the Structural Timber Association Limited's (formerly UKTFA) on-going project to develop fire design guidance and test methods aimed at mitigating the risk of fire during construction of timber frame buildings.

Is the timber treated with a preservative?

JJI-Joists are untreated and when used in a Service Class 1 or 2 environment, the ETA certificate advises that they may be taken to have a service life in excess of 50 years.

However, JJI-Joists are available with preservative treated timber flanges. This allows their use in Use Class 2 conditions in accordance with BS EN335-1, and Hazard Class 2 conditions in accordance with NHBC Standards, i.e. load bearing external wall studs and flat roof joists. This treatment does not affect the structural properties of the JJI-Joist.

Is there a technical team to help with any queries?

JJI-Joists are backed by the largest design and engineering support team in the business, based at the factory in Forres, as well as strategically placed regional sales representatives to ensure peace of mind throughout the process from specification to installation.

That sounds great! Where can I buy them?

JJI-Joists are available from a network of authorised distributors, timber frame manufacturers and other stockists located strategically throughout the UK and Ireland.

Our authorised distributors offer an estimating and design service inclusive of JJI-Joist layout plans, engineering calculations and material costings.

For more information please email or visit

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