How is your sheet metal roof fastened?
Attaching sheet metal roofs has developed slowly but surely. The development has also been necessary, as the nail fastenings of the 1960s and 1970s provided roof owners with plenty of extra maintenance work.
Roofing nails causing many problems
All carpenters know that a nail tends to rise in a structure exposed to the elements if it is not bent over (kotkata), or as it is called in some parts of Finland, kotkattu. Bending nails over on a roof is impossible. As a result, many people have gone onto their roofs to hammer down raised nails year after year. And then the nails were replaced with screws (in partly rotten battens), and finally the entire roof was replaced with a new one.
Hammer fastening itself involves two problems. The first is that the nail is often driven in too tightly, causing the seal to be ruined. The seals on nails were usually rather weak already when purchased, so the result was unpleasant. The second problem related to nails is connected to the previous one and is the final tap of the hammer. The routine of nailing includes hitting the end of the nail with a “securing” blow, which creates a dent around the roofing nail in the sheet metal that collects water. This significantly worsens the leakage problem. Experienced roof nailers knew to avoid the final blow, but accidents happened fairly certainly on every roof. And much more often with inexperienced people.
The nail could be properly said goodbye to when cordless drills became good and cheap enough. Although there are still people who do not believe that anyone has been to the moon and that a nail is not the right fastener for a sheet metal roof. Evolution is slowly reducing this group.
Long screw on the crest of the profile
The transition from nails to the current screw fastening took place slowly as methods were developed. At first, fastening was done in the same way as the former nail fastening, from the top of the profile crest. With straight-grooved profiles, fastening from the crest involves some upward movement of the screw, because thermal expansion pushes the upper part of the profile upwards and the screw’s holding force is not always sufficient to resist it. The seal also does not like the twisting caused by thermal movement. With shaped roofing, such as tile-patterned roofing, the twisting problem caused by thermal movement is less significant because the profile is more flexible.
Short roofing screw at the bottom of the profile
The development led to the current fastening method as confidence in the screw’s tightness grew with experience. Water mainly runs along the bottom of the groove, and if the seal does not hold, leakage problems are worse than when fastening from the crest. For this reason, a good screw must be used there and it must be fastened correctly. Attaching sheet metal roofing from the bottom of the profile is a more secure and reliable solution than attaching it from the crest of the profile.
But attaching sheet metal roofing from the bottom of the profile alone does not make everything perfect. A good roofing screw complying with building regulations is required. A good roofing screw withstands the climatic stress at the place of use for as long as the building itself has been designed to last and has corrosion resistance as good as the steel roofing. With a roofing screw meeting these requirements, the attachment of sheet metal roofing is reliable and durable.