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What is a JJI-Joist?

A JJI-Joist is a structurally engineered timber joist, combining high-grade softwood with an engineered composite panel. Using advanced technology these components are combined to produce an innovative alternative to conventional construction timber. They are produced on the first purpose-made I-joist production line in the UK, custom built to produce JJI-Joists to UK preferred dimensions.

Product Range & Specification

JJI-Joists are available in a range of sizes familiar to the UK Construction Industry with joist depths ranging from 145mm to 450mm. JJI-Joists are constructed from 9mm OSB web and C24 softwood flanges ranging from 47mm to 97mm in width.

Due to the unique form of the JJI-Joist European Technical Approval (ETA-10/0335), it is possible to design and produce large volumes of non-standard JJI-Joists to allow for particular span and depth situations that cannot be covered by the standard range.

James Jones & Sons Ltd. is pleased to announce our new Interactive Span Table. Visitors can enter their span and load conditions and receive a list of joists suitable for the application. Please use the link below to access this feature.

Help me specify my joist


Product Code Breakdown

joist markings

Flange Width Designations

joist designations

The standard range of products available is indicated in the following table.

Product Range Table

A+ B+ C D Timber
47mm 63mm 72mm 97mm
145mm yes

yes yes yes yes C24
220mm yes yes yes yes C24
235mm yes yes yes yes C24
245mm yes yes yes yes C24
300mm yes yes yes yes C24
350mm yes
yes yes C24
400mm yes
yes yes C24
450mm yes
yes C24

Product Tolerances

Overall Joist Length +/- 3.0
Overall Joist Depth +/- 2.0
Flange Thickness / Depth +/- 2.0
Web Thickness +/- 0.8

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