Posi-Rafter Cassettes

Thomas Armstrong Ltd, a MiTek truss and Posi-Joist manufacturer based in Cumbria, recently designed and supplied an impressive roof system to one of its timber frame projects utilising Posi-Rafter Cassettes.

The job was a new wedding venue, in a Lake District setting, for award winning local builder JJ Lattimer Builders Ltd and was designed/engineered in MiTek’s PAMIR design software and utilised the extremely flexible and versatile Posi-Rafter tools to design a high performing, cost effective and easy to install roof system.

Custom end details were incorporated into the Posi-Rafter design to allow for simple installation on-site, with large horizontal bearings built into the rafters at support positions.

PAMIR includes impressive cassette tools for Posi-Joist floors and these were used to good effect to detail the roof cassettes on this project. Posi-Joists or Rafters can be allocated to cassettes for factory output and scheduling, then clear drawings can be produced to go to site with the delivery. Designers can work on the project in cassette mode or standard mode to ensure accuracy and decking/sheathing can be drawn and scheduled accurately.

Posi-Rafters were chosen for the scheme due to the large spans required and for the ease of installation. The rafters included a large central chase opening, which combined with the void created by the metal webs to allow for a variety of services to be routed through the rafters with ease.

The cassettes were manufactured offsite in Thomas Armstrong’s production facility, ensuring quality and minimising waste on site. Cassettes are simply craned into position, massively reducing erection time and avoiding health and safety complications.

Graeme Batey, Director at Thomas Armstrong, was delighted with the way the job had turned out; “the tools in MiTek PAMIR made it simple to design and detail a solution that was ideal for the needs of this project. Posi-Rafters offer a number of benefits over solid rafters and the customer was really pleased with the efficiency and ease of installation of the design”

George Lattimer, Director at JJ Lattimer Builders Ltd, was impressed with the solution; Thomas Armstrong’s “design team worked well with our guys to get the detail correct and the kit for the superstructure, steel work and roof design was outstanding!” – Adding that, in “typical Cumbrian weather,” the speed of erection “pushed the project past our expectations.”

You can find more information on Posi-Joist and Posi-Rafter here.

If you have a job you’d like to showcase please contact Tim Garner