Structural loads on a pitched warm roof must be considered differently from those on a traditional ‘cold roof’, where the weight of the roof covering is supported directly by the rafter. On a warm roof the weight is taken up by the counterbattens, which are laid on top of the insulation, a non-structural element. The counterbatten effectively reproduces the rafter above the insulation and it is essential therefore that it becomes a structural member to which the tile batten can be fixed and, at the same time, hold down the insulation against wind suction. InSkew has been designed to do just this, resisting both the sliding and compressive loads of the roof covering while counteracting the tensile loads caused by wind uplift.
As insulation thicknesses increase so do the sliding or bending loads that are imposed on the counterbatten. The laid weight of the roof covering and the roof pitch both affect the sliding load as the heavier the tile and the steeper the roof, the greater the load becomes. However, the snow load, which must be considered in the overall assessment, starts to decline at approximately 40º.
A consequence of the sliding load is that under the weight of the roof covering the insulation could compress, impairing its thermal performance. However, InSkew, unlike traditional fixings, effectively withstands both sliding loads and compression loads.
The counterbatten (usually 25mm-50mm thick and 38mm-50mm wide) must be thick enough to grip the InSkews and enable them to resist the wind uplift. It must not buckle under the sliding load between fixings and must be wide enough to meet the manufacturers requirements for clamping the insulation. Wind suction will be affected by the anticipated wind speed, the height of the building, the site exposure and the local topography.