How To Fit Corrugated Roofing Sheets
When it comes to roofing, there’s no shortage of options. But when it comes to things like car ports, conservatories or outbuildings, you don’t want something as heavy-duty as you would for the roof of your house.
That’s where corrugated sheets come in. There’s loads of variations but two main categories: corrugated metal roofing sheets and corrugated plastic roofing sheets. Both are ideal for thee kinds of jobs and work in very similar ways to install them.
The next thing you need to know is how to fit corrugated roofing sheets. Let’s dive into that now.
Metal sheets or plastic ones?
Because you can get both metal corrugated sheets and plastic corrugated sheets, your first decision is which one to go for.
With plastic sheets, they tend to be less expensive and can have coatings on them to prevent UV rays from passing through. This cuts down the chance of UV damage but still lets in plenty of light. They are ideal for things like car ports and conservatories. They aren’t as strong as metal sheets and there’s more noise from things like rain.
Metal sheets block the sun’s rays but do tend to heat up when the sun is on them. This can be a good thing but not always - it depends on the space below. Metal sheets are very durable and will withstand the worst of the weather. People favour them for outbuildings and areas that don’t get direct sunlight - or where they don’t want the sunlight inside.
Choosing the roofing sheets
Before we dive into how to fit corrugated roofing sheets, let’s take a moment to be sure you get the right ones. There are various brands out there to choose from with good makes having a specific time guarantee and requiring very little in the way of maintenance.
The main thing you need to decide is what thickness you want. Common sheet weights include lightweight (0.8mm), heavy-duty (1.1mm) and super weight (1.3mm). You can get clear or a range of translucent tints on the plastic versions or different finishes on metal ones.
How to fit corrugated roofing sheets
Once you know what sheets you want and have them on-site, you are ready to start the process of fitting them. This process assumes you have the framework in place to add the corrugated roofing, if not that would be your first step.
Step 1 - Cut the panels to size
The first step is to get the panels cut to size if this wasn’t done before delivery. Most panels come in standard lengths and you also need to allow for a minimum of 46cm (18 inches) if you need to lap to complete the roof.
Also, allow for at least 60mm overlap to overhang the roof to help with rain runoff into the guttering.
There are a few types of cutting tools to use, depending on whether you gave metal or plastic sheets:
- Angle grinder - quickest option and will cut either metal or plastic. Make sure you wear protective gear and paint cut edges on metal sheets with primer to stop rust
- Circular saw - slower but otherwise much the same. Cutting metal will wear the blade quickly so have replacements handy
- Nibbler - can work on metal if it is the right gauge for the job
- Tin snips - will work in plastic and some thinner metal but will take a lot longer and a lot more labour-intensive. Make sure you wear gloves
Expert tip: Avoid cutting plastic sheets in cold weather as this can make them more likely to break. If you do need to work in the cold, keep them in a warm room until you are ready to make the cut.
Step 2 - Pre-drill the holes
Some corrugated roofing may come with pre-drilled holes but if yours doesn’t, then you want to do this first. Ideally, a 4.8mm (3/16th inch) drill bit will do the job.
Add a hole every 15-20 cm (6-8 inches) along the exterior edges of the panels. Make sure you have at least 5 fixings per support across the width of the sheet.
Step 3 - Add the panels to the framework
Now you are ready to fit the corrugated sheets onto the framework you have created for them. Start at one end of the roof and use a wood or plastic strip under the end panel. This stops the water and wind getting in and also reinforces the end of the roof.
Alternatively, some corrugated roof panel ranges will have their own flashing. These will match the sheet and cover the ends with special tape. The tape creates a waterproof seal between the flashing and the sheet to stop water from getting in.
Step 4 - Screw down the panels
Ideally, you want screws that are something like 25 x 5 cm (10 x 2 inches) with special polycarbonate washers on them for plastic sheets or metal ones for metal sheets. The washers will sit between the screw head and the sheet to stop the wind pulling it off.
Start screwing in from the end and adding more sheets. Don’t overtighten the screws - make sure the washer can be turned with your finger and thumb as a gauge of how much to screw in.
Make sure you overlap each sheet by at least 150mm for a 10-degree slope or double that for a 5-degree slope. For the last panel, adjust it as far in as you need so the edge lines with the end of the roof area. Use the flashing or sealed system the same as the first edge.
Corrugated roof tips
To get the best results with corrugated roofing sheets, try to start with a corner that’s away from the direction of the prevailing winds (where the wind most often comes from). This helps to prevent the side laps facing the worst of the weather.
If you are fitting the roof under existing eaves, make sure that it goes over the bottom purlin and the eaves so that rainwater continues to guttering or beyond the wall.
For metal sheet projects, make sure you have enough people to comfortably lift the panels. Plastic is relatively lightweight but the metal sheets are heavier and you’ll probably need more people to lift it into place and hold it while you screw it in.
What if there are protrusions?
Protrusions can be anything from pipes and ducts to airconditioning units. These are things that need to pass through the sheet and be on the outside of it. This is relatively easy to do with both types of corrugated sheet.
What you do need to do is make sure you have the right flashings to go around the protrusion and stop the water from getting through. This creates a seal around the protrusion and ensures weatherproofing.
Corrugated roofing sheets are a top-quality way to finish lots of projects from car ports to outbuildings. The variation of styles means there’s something for all requirements and they are easy to work with and fit yourself, with a few helpers!