ASSY^® Isotop wood screw

Roof application 1

• For soft insulation <, with a compressive strength of less than 0.06 N/mm²

For soft insulation with resistance to pressure of less than 0.06 N/mm² such as glass wool, rockwool, ecological insulation = use an alternative screwing method with an angle of 60° to the joist plank.

Roof application 2

• For "hard" insulation, with a compressive strength of > 0.06 N/mm²

For non-slip insulation with resistance to pressure exceeding 0.06 N/mm² such as polyurethane foam (PUR) or polystyrene (PDS) = parallel screwing method with an angle of 60° to the joist plank.

Required screw length calculation:

• Counter-batten thickness in mm


• + insulation thickness in mm


• + panelling thickness in mm


• + 60 mm screw-in depth

Partial result in mm x slope factor of 1.15

• Final result in mm


• Use a screw that is larger than the resulting figure

Further product documentation:

• Würth dimensioning software, (available online, or you can download it for offline use)


• Dimensioning software, data sheets and European technical assessments can be found on our website www.wuerth.it/assy


• Data sheet for over-rafter insulation