We are an authorised distributor of James Jones & Sons timber i-joists.

The JJI Joist is a structural, engineered timber i-joist, manufactured to UK preferred dimensions. Ideally suited for both residential and commercial applications, JJI Joists are available in a range of sizes (see our product comparison chart below for more information) and are FSCĀ® and PAS 2050 accredited.

Product features and specifications

Superior strength

With a high strength to weight ratio, i-joists can be supplied in longer lengths than solid timber.

Quicker to install

I-joists weigh much less than solid timber joists, so are easier and faster to install.

High structural efficiency

I-joists don’t bow, warp or split, so your building will be stronger.

David Smith St Ives - I-joists for Sarek Roundhouse project

Durability and treatment


Standard product

JJI-Joists are untreated and when used in a Service Class 1 or 2 environment, the European Technical Assessment (ETA) certificate advises that the joists can be expected to have a service life in excess of 50 years.

Preservative treatment

JJI-Joists are also 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. This treatment does not affect the structural properties of the JJI-Joist. Please note a minimum order quantity will apply.

Tell us about your project

Compare joist depths and sizes

Joist depth A+ B+ C D
47mm 63mm 72mm 97mm

Download the Site Construction and Hole Guide

View the Interactive Span Table

Speak to an expert

Adam Ding

We've worked with David Smith st Ives for a very long time. We need suppliers who can cope with our workload, and David Smith St Ives has plenty of capacity.

Kevin Dundas, Supply Chain Manager, Willmott Dixon

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