How To Install Roof Sheeting
Once you have settled on the material you will be using for the roof, the next stage is the installation. This is the most important stage because if you get the procedure right you will maximise the value of the material over the years as it will experience less damage and require fewer repairs.
From measuring the roof correctly to layering and securing the sheets, our guide on how to install roof sheeting will tell you what you should do to install your roof sheeting safely and correctly. In addition, always follow the instructions provided with the product as instructions may vary slightly depending on the material.
How To Measure The Roof
The measurements needed for roofing sheets will be based on the type of roof you have. There are four common roof types which should be measured as follows:
Mono pitch roof (single slope): These are usually found on garages and carport roofs. In some cases, the width of a mono roof can be larger than the actual length of the sheets. The good news is they are the easiest type of roof to measure. Start by measuring the width to find out how many sheets you will need. To calculate the length of the sheets, measure the length of the roof.
Apex roof (double slope): Apex roofs can sometimes be uneven but in most cases are equally divided. This will mean that the length of the sheets can sometimes differ on each side. You must measure the ridge length to discover the number of sheets you will need for each side. Next, measure the ridge to eaves to calculate the length of the sheets. If the apex is not even you will have to repeat this process separately on both sides of the roof.
Adjoining apex roofs: An adjoining apex roof features one or more apex roofs all connected with each other. To get the right measurements for a T-shaped roof, they are separated into two calculations – one for each section. Measure the ridge on the main apex to figure out the number of sheets needed, while the ridge to eaves measurement will dictate the sheet lengths. The same process is repeated for the smaller adjoining apex.
An L-shaped adjoining apex roof is more complex and has to be broken down into four measurements. Follow the same process of measuring the apex on each side to calculate the sheet quantity, then measure the ridge to eaves on each section of the roof.
Hipped roofs: A hipped roof will require four-panel sections due to the make-up of the design. Measurements need to be taken along all of the gutter lines for each section along with the ridge to eaves. This will determine the number of sheets required and also the length.
Layering Roof Sheeting
When laying down the sheets onto the roof you should begin at the eaves end of the roof, ensuring they are sheltered away from the general direction of the wind. This will ensure you get maximum weatherproofing from the wind and any water ingress.
On square buildings you should check the first sheet is laid perpendicular to the eaves and ridge. If the roof is of a different shape you may have to make adjustments to the sheets as each one is laid down.
Make sure the sheets are the right way round when at ground level, instead of turning them over once up on the roof. It also makes sense not to permanently fix down the first few sheets so you can make sure everything is aligned correctly and you can make the necessary adjustments if needed.
Overlapping Roof Sheeting
To overlap the sheets with one position partially over the top of the other, ensure at least one profile in the next run overlaps the previous panel. These are called side laps. End laps are made up of adjacent sheets and should overlap by at least 25cm. Doing this will ensure there are no gaps for rainwater to penetrate once the sheets have been fixed into place. Check that the first row of sheets on the roof are hanging over the lower purlin and eaves as this will allow water to flow off the roof easily.
Fixing & Securing
To create the holes for the screws you should always use a drill that will create holes 2mm larger than the fastener diameter. Follow the rule of 2 fasteners per sheet per purlin and do not use punches to make the holes in the sheet as these will not be sufficient.
Topfix fasteners are a good choice as they can be drilled through the sheet to open up the hole and drill down into the purlin below. This brand also comes with an integral sealing washer included. The type of fastener you choose will depend on the type of sheet, roof pitch and purlin type.
Use sealing washers and caps with traditional fasteners, which could be crook bolts for zed purlins, M8 x 120mm drive screws for timber and hook bolts for angle section purlins. Position the fasteners to the side of the lap on the first full sheets, and for end laps space them 50mm apart from the upper end of the lap.
Supporting Roof Sheeting
The purlins are there to ensure there is enough support to bear the weight of the sheets on the roof, making up part of the framework of the structure. Depending on the span, the recommended minimum size for timber purlins is 50mm x 100mm, while steel purlins should be no less than 140mm x 1.6mm. The purlin joints should also be supported by a rafter which is connected using cleats.
There isn’t an extensive list of tools required for installing roof sheeting. In most cases, it will be a case of measuring, laying and securing the sheets correctly on the surface.
- Measuring tape
- Circular saw/Fine tooth Saw/Stanley knife (this depends if sheets need to be cut on site for non-standard shaped roofs.