Correct length for combination(fasteners)
It can happen to anyone. At the start of the project, the supplied fasteners turn out to be too short for the structure on the roof. This will immediately delay the project! Asking “What insulation thickness is used?” sounds easy, but things can still go wrong. Below, we briefly explain what to look out for when ordering our Guardian products, to ensure that the right combinations are delivered to the roof.
Substrates
There are different installation depths for each substrate. By installation depth we mean how far a fastener should sit or protrude in the substrate. We usually indicate this in millimetres (mm). The following table gives an overview of the most common substrates with the corresponding installation depths.
|
Substrates |
Minimum installation depth (mm) |
Pre-drilling |
|
Steel |
20mm |
No |
|
Wood |
25mm |
No |
|
Concrete |
25mm* |
Yes (Ø5mm, 35mm minimum) |
|
Light-weight concrete |
60mm |
No |
|
Other |
Please contact us |
– |
* If fasteners longer than 100mm are used, an installation depth of 30mm is recommended.
Differences in substrates
Substrates, especially precast concrete and steel profiles, can cause different mounting thicknesses to arise. Why this is?
Hot roof plates have different ‘dimples’ which ensure the strength/stability of the plates. However, these ‘dimples’ can be so large that a fastener combination no longer has the correct installation depth at the level of the dimple, or does not even grasp the substrate at all. The simplest solution for these situations is to use a fastener combination with a 10mm longer installation depth.
Precast concrete slabs can have different heights. The cause is often the execution of the work. Here too, a longer combination may be necessary due to the use of, for example, hard insulation panels at the level of two precast concrete panels. The ideal solution for this is to use the Guardian ASTL combination. More information about the Guardian ASTL can be found on our website.
Type of roofing and damp screens
When determining the right fastener combination, take into account the thickness of the roof covering and any damp screens. Standard combinations show the maximum mounting thickness that can be achieved, taking into account the installation depth. Particularly when renovating, several old roofing layers may require a longer combination. In this type of situation, always measure the structure including the old roof covering.
Composition of the combination
In some situations it is necessary to deviate from the standard combinations. It is then good to know that in a combination where a nylon tube is used, the screw loses 20mm of its length in the tube. In order to maintain a telescopic effect, the nose of the tube should be approximately 20mm from the surface. It is easy to determine the right fastener combination for using the Guardian R-45 and R-75 using the photo and formula below.
Maximum tube length (mm) = Total mounting thickness (mm) - 20mm
Round down the tube length.
Length of fastener (mm) = (Total mounting thickness (mm) - Tube length (mm)) + 20 mm + installation depth
Round up the length of the fastener.