Anyone who passed Persimmon’s Blyth development on their way to work on the morning of July 31 and noticed the shell of walls forming two semi-detached houses, may have been surprised on their homeward journey to see that the building had been topped out, and was just awaiting the finishing touches of roof tiles.

All panels for both plots loaded onto one truck

Using the JJ-IntelliRoof it had taken just under eight hours to install two attic roofs, complete with floor cassettes and spandrel panels, and make them wind and watertight. In comparison, said Chris Curry, construction director at Persimmon Homes (North East) Ltd, it could have taken two to three weeks to reach the same stage with a standard attic truss system.

James Jones & Sons developed the panellised roof system in response to the construction industry’s call for faster and safer ways to erect roofs. “Builders have been crying out for safer ways to build rooms in the roof,” said Ross Brown, James Jones development engineer. “The traditional alternative is an attic truss which is built truss by truss then it’s raised and decked. That’s quite a dangerous environment; there’s a lot of timber criss-crossing and there’s not a safe area to work from.”

All floor cassettes in place

The finished roof panels of the JJ-IntelliRoof comprise a plasterboard lining on the underside of the bottom flange of a JJI-Joist, while on the upper side of the bottom flange a 9mm OSB3 panel and vapour barrier create a service void and hold the insulation in place for the remaining depth of the I-joist. A final layer of 9mm OSB topped with a breathable roofing felt and counter battens secured along the lines of the I-beam rafters complete the panel and all that remains is for the tiling battens to be fixed before tiling.

The floor cassettes are JJI-Joist floor cassettes decked with 22mm chipboard and a glulam rimbeam around the external edge. They include all the trimmings for the stairwell, complete with temporary crash deck. The spandrel panels are standard timber frame construction – 38x89mm CLS stud sheathed in 9mm OSB, with a breather paper fixed to the external side.

Top hat assemblies for both plots made up at ground level ready for lifting onto the lower spandrel panels

Installing the IntelliRoof is carefully choreographed, from loading the cassettes onto the lorry (the 40 required for the two Persimmon houses fitted on just one standard, flat-bed lorry) to the fitting of the final roof panel.

The first procedure in the installation is to ensure there is a flat and level wall plate on the structure, whether it’s masonry, steel or timber frame. Then the pre-assembled floor cassettes are craned into place, creating a safe working platform; a sole plate is placed around the perimeter of the structure and the lower level spandrel panels are fixed into position.

One of the top hat assemblies being lifted into place

Once this is completed, assembly of the top hat section – the ceiling cassette and the two upper spandrel panels – is done at ground level. When this is lifted into place it provides the floor to the loft – and a second safe working platform for the erection team. The prefabricated roof cassettes are then brought in and any laps in the roofing felt are made good to ensure the whole envelope is watertight.

First roof panel lifted on to substructure

Ross Brown describes the IntelliRoof as “just normal timber engineering” but, because of the pre-assembly, and because it is supplied and fitted by James Jones distributors who have trained erection teams, the builder doesn’t have to worry about having to find skilled joiners. There is the added benefit of reduced site waste as the prefabricated system should fit perfectly.

“As long as there’s a flat level wall plate then all the builder has to do is phone to say he wants a roof at this time and this date, and the guys will turn up with a lorry,” said Brown.

View from inside as a roof panel is installed

James Jones expects the system to appeal to large housebuilders with a lot of repeat business and tight turnarounds. “You can cut at least a couple of weeks – probably more – off your build programme,” said Ross.

And the advantages to builders working on tight sites are two-fold: there is no need to take up space storing materials as the operation can be completed in a day; and it enables a room in the roof to be easily added to a house with a small footprint.

Top hat assembly slotting into place on top of the previously installed lower spandrel panels

“It’s for builders who already have a room in the roof and who want to build faster and in a safer manner, or for people who want to convert existing designs by adding another room on top,” said Brown.

The completed substructure for both plots ready for the roof panels

"Not only does the system reduce the health and safety risks from working at height but, if I can erect two or possibly three roofs in a day, I can make considerable savings in my build progrmame," said Chris Curry of Persimmon Homes.