ISSUE
Tectum is a roof decking material that has been used primarily for institutional applications. In many cases, the bottom side of the Tectum is visible from inside the building. Tectum can be identified by its “shredded wheat” appearance from the bottom side.
ANALYSIS
In some cases, Tectum has been installed on very low pitched roofs. In other cases, though, it is on steeper roofs and asphalt shingles have been applied to it. For secure fastening, asphalt shingles are usually installed on Tectum with “hook nails” which are nails that are inside a tube. When they are driven in, they are directed by the tube into a hook shape for a tighter bite.
SOLUTION
If metal roofing is to be installed over Tectum, ensure that the roof pitch meets any requirements posed by the product being installed. For re-roofing over Tectum, keep in mind that Tectum can soften as it ages. Additionally, if hook nails were used to install the previous roof, it will be impossible to remove the old roofing without destroying the Tectum decking. For that reason, low weight metal roof systems can be a very good option. Because Tectum will deteriorate when moisture or frost reaches it, ensure that the building has proper ventilation so that moisture will not condense in or on the Tectum decking. Metal roofing should be installed over Tectum using self-drilling, self-tapping screws of similar metal and of sufficient length to go well into the Tectum. Do not use fasteners that are long enough to fully penetrate the Tectum. Prior to starting roof installation, ensure that suitable pull-out resistance can be obtained using the desired fastener. If the Tectum is extremely soft, the only choice may be to remove and replace it.
