Metal Web Joists also known as Posi Joists or Open Web Joists are an innovative and versatile floor joist system which is popular with house builders, commercial property developers, architects and engineers for all domestic, industrial and commercial projects.


Thomas Armstrong (Timber) Ltd are a licensed MiTek Manufacturer to design, manufacture and supply Posi-Joist™. Our Metal Web Joists are all bespoke to our client’s specification and to ensure they meet all current codes and standards. They are ideal for timber frame structures, traditional build, complex and ambitious self-build projects and large apartment blocks or hotels.

All buildings are unique, so our dedicated teams have the in-depth experience and knowledge to design, manufacture and supply metal web joists to your specific requirements using the very latest in design and engineering software.

Our Metal Web Joists have an ‘open-web’ design which is achieved through the lightweight qualities of the parallel timber flanges (or chords) joined with the strength of the engineered V-shaped steel webs. A key advantage of our ‘open-web’ design provides clear and fast access for the installation of services such as plumbing, electrical, pipework, cabling and other services which prevents the requirement of notching or drilling. This saves time on site due to the easy access and convenience to work.

This innovative floor joist system is lightweight yet high strength so larger lengths up to 12 metres can be achieved, giving more design flexibility and freedom than solid joists or timber products. They also minimises squeaky floors, sound and vibrations.

This system has the capability to be suitable for use on flat, pitched roofs and are known as Posi Rafters.

Along with our exceptional customer service, the quality of our engineered roof products is important to us, with our metal web joists being manufactured to the highest quality using timber responsibly sourced under the Programme for the Endorsement of Forest Certification (PEFC) scheme. We have always continued to meet the latest developments within the industry, so all our trusses are manufactured to BS EN 1995-1-1 (Eurocode 5) and EN 14250 and under ISO 9001.


One key advantage is at Thomas Armstrong (Timber) Ltd, we supply all the relevant timber ancillaries’ items as standard. Depending on the timber product/s ordered, ancillaries items such as straps, hangers, timbers, truss clips, gable straps, valley gutters etc are delivered at the same time ensuring you have everything you need to complete the installation of our products on-site.



  • Suitable for a wide range of building types
  • Improved Sound and Vibration performance
  • Long continuous spans and multispans
  • Easy access and quick installation of services
  • Manufactured off site
  • Engineered product that provides greater level of precision and accuracy
  • Easily transported and ready for installation on delivery
  • Prefabricated components mean reduced site labour costs
  • Increase dimensional stability over solid timber joists



  • House extensions
  • Self builds
  • Housing schemes
  • Barn conversions
  • Apartments
  • Student accommodation

Commercial buildings, including:

  • Schools
  • Nursing homes
  • Hospitals
  • Offices
Why choose Thomas Armstrong?

Thomas Armstrong (Timber) Ltd have been to be a leading timber roof truss manufacturer, servicing sites across the North of England and Scotland. To discover why to choose Thomas Armstrong (Timber) Ltd then click here for more information.

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Other Products Available

At Thomas Armstrong (Timber) Ltd, we provide a range of timber products to support you with your build project including:

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Supporting you with your build project
Thomas Armstrong (Timber) Ltd is part of the Thomas Armstrong Group, as we can provide a ‘one stop’ service as we have the skills, capabilities and knowledge to help support you with your entire build project. Other services of interest include: