To optimize the benefits of the tube system, the ideal combination is to use the maximum length of tube and the minimum fastener length available. However, in certain applications, such as over-roofing existing membrane and insulation layers, different tube lengths may be required. Contact our sales office for details. The tube washer must be chosen first, then the fastener can be selected.To select the maximum tube length (B), deduct 20mm from the total build-up of the roof system to allow for (A) compression of the insulation. Choose the tube of that length or shorter.For example, with an 85mm build-up and a requirement for an R-75 tube washer the maximum tube length would be 65mm, so the 60mm long R-75 x 60 would be chosen:Selecting the Correct FastenerWhen selecting fasteners, allow for the recommended minimum deck penetration or embedment and take into consideration the total build-up of the roof system, including any pressure plate, membrane, insulation, vapour control or separation layers.To select the optimum fastener for tube washer applications, take the total build-up measurement, deduct the selected tube length and allow for deck penetration. Then add 25mm for the fastener within the tube and select the fastener at this length or longer.For example, with an 85mm build-up over 0.7mm steel deck using a 60mm tube; and using the BS-5.8 range of fasteners.