One I made earlier - By Chris Thomas

One I made earlier - By Chris Thomas

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The Egan agenda is rapidly driving the construction industry into a new era of off-site construction. But to date, roofs have been largely resistant to this trend. Chris Thomas wonders why this should be so, and considers the range
	Vencel Resil's Jablite structural insulated roof system (above). Opstalan's hinged roof panels with built-in rooflights (left). Installation of Kingspan's TEK Haus structural insulated roof panels (below)
Building components are being delivered to site in ever larger modules: hotel rooms, offices and whole class rooms now routinely arrive this way. Yet in the majority of cases the roof is still constructed in the traditional manner. Once a crane is required on site to lift the large modularized components from the back of a truck into their final position, it would seem logical to use the same crane to install the pitched roof. On the majority of modular building projects the pitched roof is either constructed using timber-trussed rafters or unclad panel structures. Whilst some contractors have experimented with assembling trussed rafter roofs on the ground, including felt and battens, and lifting them into position with a crane, there is a lot of site work and space required to achieve what is still a site produced roof construction. Timber Roof Panels The Dutch have embraced the use of factory produced timber roof panels in a big way to suit their style of housing. Opstalan are one of the better known manufacturers of structural diaphragm roofing panels. The panels can be up to 2.4m wide and 10m long to span from ridge to eaves In one unit. The panels comprise timber rafters clad top and bottom with plywood panels filled with insulation. Some come with battens, underlay and roof windows already installed, requiring only the tiles to be installed. This form of roof construction works well on long gable-to-gable buildings such as terraced houses with rooms in the roof. The introduction of hips and valleys in the roof shape can be accommodated, but will reduce the advantages of such a system. With the hinged panel design, two panels joined at the ridge can be installed at the same time with benefits in accuracy and speed.
		The Jablite Roof Element system from Vencel Resil is a less complicated version of the same thing with all panels 1.01m wide and In lengths between 3.92 and 7.52m. The panels can be supplied cut to a mitre at the ridge, but all have square cut eaves. The narrower panels make forming hips and valleys a lot easier, but a crane is still required to lift the panels into position. The panels come with timber upstands, making it appear like a normal roof to a roofer who will still need to fix underlay and battens prior to finishing the roof with slates or tiles. With no trusses or beams, full use can be made of the loft space. Kingspan Insulation have recently introduced the TEK Haus building system which incorporates structural insulated roof panels similar to that of the Opstalan system, but without the intermediate timber members to act as a cold bridge. This makes for a very thermally efficient panel, but relies on the bond of the OSB board skins with the rigid urethane core to transmit some of the structural loads. The roof panels come smooth and need to be covered with counter battens, underlay and battens before the roof tiles can be fixed

Metal Roof Panels
The use of Tactray 90 steel liner trays from Hironville TAG, as used on commercial buildings, to reduce the need for a timber roof structure on a steel framed building, requires a lot of site work to achieve a quick roof substructure. The system is ideal for wide span buildings. Once screwed together it makes a very secure platform for the roofing work and a safe environment below to allow other trades to work. The square cut ends to the sheets make hips and valleys cumbersome, and the detailing of the ridge and eaves not as simple as with timber trussed rafters, making the system ideal for large simple roof designs.
An alternative approach is that of the composite metal panel as promoted by Kingspan Building Products. This uses two thin sheets of profiled steel sheet with rigid insulation between. The composite panels can be installed quickly to produce a weather-tight roof before battens are screw- fixed to the corrugations to accommodate conventional tiles or slates. The integration of the panels with a steel frame building makes this form of construction better suited to wide span commercial buildings than to housing.
Ward Building Components has taken the composite panel one stage further with the development of a composite metal panel with the upper sheet pressed to represent an array of pan tiles, thus providing an insulated panel with a tile-look finish. A single-fix installation directly onto purlins eliminates the need for battens, roof felt and separate insulation materials thus speeding up build times. Its lightweight construction also enables structural support savings to be made. The Ward system can accommodate hips and valleys but is best suited to wide span steel frame buildings.

Instant Roof
To truly take advantage of factory produced modular construction the pitched roof also needs to arrive ready for installation with a minimum of finishing on site. Hanson TIS, with its new Modular House, has developed one solution to this problem, using four factory finished modules clamped together on site. Two modules make the ground floor accommodation, the other two form the first floor accommodation. The upper two units arrive with a traditional tiled roof already installed. Once a crane has lifted each unit into place, the lifting hooks are removed, the modules clamped together, the flashing between the two sections of the building installed, the plumbing and electrical connections checked and the building is ready for occupation within a few hours.
This system appears to satisfy all the demands of developers, planners, customers and the Health and Safety Executive. It is equally suitable for executive homes and social housing, with the speed and quality that would be almost impossible to achieve with any other modular building system with a pitched roof.

The Future
With the rising cost of energy and the need to control the deterioration of our environment, it will not be long before legislation compels all south facing walls and roofs too consist of solar panels to harness energy from the sun.

Already the JOULE European research project has produced PRIDE, a modular factory produced solar roof panel ready to install. The system is similar to the Opstalan panel with the solar panels ready fitted and cabled ready to connect to a suitable inverter.

I am sure the development of factory produced pitched roofs will help to overcome the shortage of good roofing craftsmen, cut delays due to bad weather, shorten snagging lists and reduce accidents on site to a minimum. One way or another, factory produced roofs are long overdue.

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