Determining The Correct Roofing Fastener Length When Fixing into Timber Substrate.

TimTapp Timber Roofing Fasteners

Once you’ve decided on your metal roof sheeting profile and material, how do you determine the correct roofing fastener length to use for your installation?

Finding the Correct Roofing Fastener Length when Installing Pierced Fixed Profiles (Corrugated, IBR, Widespan).

When installing into timber you need to know what the minimum timber depth penetration needs to be. This is determined based on the fastener manufacturer specification or recommendation.

At Corroshield South Africa (CSSA) we recommend a minimum timber depth penetration of 30mm for our Corroshield and Tapperman roofing screws.

Now that you know the minimum depth needed, next you’ll need to determine the Roof Sheet Profile Crest/Rib height as well as roof sheeting material thickness. Your roof sheeting provider should be able to provide you with this information.

With all this information in hand, the formula for determining the length will be:

Crest height + material thickness + minimum timber depth recommended.

Concealed Fix Clips into timber 1

If you are installing a Corrugated roof sheeting profile with a crest height of 19mm and material thickness of 0.53mm, the fastener length required will be 19mm + 0.53mm + 30mm minimum timber depth penetration equalling 49.53mm.

Based on your calculations, find the fastener length available closest to the available stock length. At CSSA we stock a standard length of 50mm and 65mm for Corrugated and Widespan applications.

If you are installing insulation over purlin the insulation thickness needs to be taken into consideration as well in determining the fastener length.

Finding the Correct Roofing Fastener Length when Installing Concealed/Secret Fixed Profiles.

Concealed fix systems are installed using a clip system that is secured to the structure, the roof sheet is held in place by the clip.

At CSSA for concealed fix systems we recommend a minimum timber depth penetration of 40mm for our Corroshield and Tapperman roofing screws.

Determining this roofing screw length, you will need to know the thickness of the concealed fix clip. Should the clip thickness be 1.25mm, the fastener length required will be 1.25mm + 40mm equals 41.25mm.

Based on your calculations, find the fastener length available closest to the available stock length. At CSSA we stock a standard length of 45mm for concealed fix systems.

Determining The Correct Roofing Fastener Length When Fixing into Timber Substrate

If you are installing insulation over purlin the insulation thickness needs to be taken into consideration as well in determining the fastener length.

When installing pierced fix applications Hex Washer Flanged fastener heads are recommended, when installing Concealed fix systems, depending on your supplier wafer heads are recommended.

It is important to note that the length being calculated is determined from the underside of the fastener head to the tip of the point of the fastener.

Have a look at our Fastener Application Guide for ease of reference.