Metal roofing tiles have come a long way since their introduction 50 years ago. The first tiles introduced had a bitumen coating which tended to melt in hot climates. Premium modern finishes are acrylic and are guaranteed to last in excess of 50 years.
Metal roofing offers a lightweight alternative to the heavier concrete and clay tiles they imitate. Weighing less than a third of the weight of a concrete covering, they require a less substantial structure to support the roof. This brings the build cost down and offers more flexibility with structure choice. The installation time of metal roofing is much quicker than that of clay or concrete. This also reduces labour costs and allows the second fix trades to commence earlier. Each roofing manufacturer will provide an installation guide for their product. Here are a few extra installation techniques not normally covered.
Setting out the roofing before installation is a major part of any new roof build. With metal tile roofing it is imperative to get the correct gauge right from the start. Unlike concrete tiles that have a certain amount of play in the gauge measurements, metal tiles have to be spot on or they will not fit. For this reason it is common practice to use set out pins to ensure accurate fixing of the batons. A measuring stick is used to mark the gauge up the rafter, before driving in the set out pins. The batons are then cut in place before being lifted clear to allow the building paper to be laid. It is possible to cut down the setting out time by half by building a separate, smaller gauging rod. The smaller rod is used to fix batons around hips and valleys and saves a lot of time messing around with a tape.
Cutting and bending
At roof terminations and intersections tiles are cut to fit allowing for a 50mm bend in the tile. It is this turn up/down that provides the waterproofing of the roof. It is important to bend a sufficient upturn or water may be blown under the ridge or hip.
I have found by taping the jaws of the bender with several layers of duct tape, it allows the tiles to be gripped firmer without damaging the paint of the tile. Aim to use half the tile per cut. This will leave you enough metal to get another cut for the opposing side.
Marking and cutting the valley at ground level gives a much neater appearance. Instead of measuring each tile cut individually, the tiles are laid along the ground as if they were on the roof. The tiles must be tight and correctly aligned. The bottom and top course is then marked using a bevel. Two people may now chalk a line along the length of the valley. This gives a much straighter line than individual measurements.
Laying the tiles
Contrary to other roofing practices, pressed steel tiles are best laid from the ridge down. Lay the under lap into the prevailing wind. This will ensure the maximum wind resistance and stop the roof lifting.
The first full top course is laid out and fixed at the head of the tile, allowing the subsequent row to be slid underneath the bottom. It is important to even out the tiles to make the best use of the cut ends. By finishing the tiles 450mm from the end of each verge it will allow two cuts to be made from one tile. In windy conditions it is a good idea to lay four rows at a time before nailing the top 3 courses. As with all roofing, foot traffic should be kept to a minimum. By walking directly above the fixed baton you will prevent any denting of the surface.
When it comes to the final installation of ridge and hip tiles, take extra care with the “cutting in” at intersections. The aim is to provide a watertight seal using correctly folded cuts rather than using silicone to keep the water out. By spending a little extra time with your cutting and bending, the roof will have a neat appearance and give years of maintenance free service.