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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.


Flange Width DesignationsThey 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 PAS2050 accredited.

The Joists are available in depths from  145mm up to 450mm deep with four flange sizes to facilitate a high degree of design optimisation putting the right product in the right place. The four flange widths are illustrated below along with a table showing the full range of JJI-Joists available.

JJI-Joists are sold through a network of distributors, which you can find by looking at the map below, or downloading the Distibution Map from the download panel on the right.


Product Range Table

Joist depth A+ B+ C D
  47mm 63mm 72mm 97mm
145mm yes      
yes yes yes yes
220mm yes yes yes yes
235mm yes yes yes yes
245mm yes yes yes yes
300mm yes yes yes yes
350mm  yes  yes yes yes
400mm  yes  yes yes yes
450mm  yes  yes  yes yes



 Find a JJI-Joist distributor

View James Jones & Sons TSD-Stockists in a larger map


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. 

Due to the unique form of the JJI-Joist TRADA ETA certification, 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.  Bespoke lengths are also available to order.



Flame retardant (FR) treatment

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.

As part of this work we have performed fire tests with flame retardants from two manufacturers with positive results. Where there is no alternative it is possible for us to supply a non-standard FR treated joist that complies with the Structural Timber Association Limited FR build requirements.

Pricing and delivery times on application.

Durability and treatment

Standard product

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. 

Preservative treatment

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. Please contact James Jones and Sons for further information.

Where to buy

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. 

Timber Systems Division contact

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