The counter battens are mounted with wire pins above the underlay, in the middle of each rafter and, in addition to transmitting power from the support friction or the full formwork to the rafters and the constructive protection of the support friction from moisture, primarily serve to ventilate the roof covering. The design of the counter battens depends on the required rear ventilation, the selected undercover and static specifications. [...]
The rear ventilation level under the tile roof prevents damage to the underside of the tiles due to condensation and improves the thermal insulation of the attic in summer. As a rule, counter battens measuring 30 x 50 mm are installed for rear ventilation. From a counter batten length of 12 m, counter battens with 40 x 60 mm must be used. From a length of 18 m, the required height is already 50 mm. For the exact dimensioning of the ventilation cross-sections, the minimum ventilation cross-sections for ventilated roofs from the ZVDH's "Leaflet on Thermal Protection for Roofs and Walls" are used.
But the sub-roof can also influence the counter-batten cross-sections. Underlays and on-roof insulation made of wood fibre boards have a lower strength than, for example, wooden formwork. From certain panel thicknesses, special nails or screws must be used to fasten the counter battens, which require a larger counter batten cross-section. In general, however, it should be noted that when using a roof panel, e.g. made of wood fibre, the counter battens should be increased to a thickness of 40 mm (40 x 60 mm). This ensures that the wind-suction-stressed support rails or full formwork are adequately fastened. Otherwise, special nails such as twist or threaded nails must be used.
Source: bauwion
