Double-threaded screws for fastening insulation systems

This compression of the insulation can be prevented by using double-threaded screws, which have an additional thread below the head in addition to the regular thread at the screw’s tip. The screw has a smooth shaft between the threads. As a result, this screw geometry can fulfil two tasks. The bottom head screw serves to position the counter batten and keep it spaced from rafters, preventing the roofing from pressing on the insulation material. The second task is to anchor the screws into the timber rafters or the CLT element, where the forces are transferred directly between the two structure elements – almost like a rigid body movement – but without affecting the soft layer of insulation. Installing these screws in an inclined arrangement is a good choice, since this creates compressive stress in the vertical screws and conversely creates tensile strength on the inclined screws.

Generally speaking, the thicker the layer of insulation, the better the thermal performance. But even longer screws need to have an increased compressive length and thus a reduction in their final capacity. In any case, a careful analysis is indispensable for finding a cost-effective solution.

Please consult certification ETA-11/0024 for more individual details regarding this matter.