How to install a GRP Roof on my shed

Home Roofs How to install a GRP Roof on my shed
GRP Shed Roof

GRP roofs are a very common solution for sheds because they are perfect for insulating it and protecting it from rainfall and moisture, keeping your tools and whatever else you might have in there in good condition. What’s more, they are efficient and cost-effective, taking less time and labour to install. Here, we’re going to look at how you can install a GRP roof on your shed.

Fitting your decking

First of all, if you’re removing an old roof, inspect the decking. If the wood is still in good condition, you simply need to overboard it. If it has been compromised by moisture, is weak and flaky, or is sloping or bent, you need to replace it. Either way, 18mm OSB3 decking boards are the material of choice. Lay them at 90 degrees to the joists with the writing side facing upwards. Lay them from the furthest edge from the drip, allowing for a 25mm gap between the boards and the wall. Align the end of the boards with the fascia and make sure the last board is trimmed to be flush with it. A second row should be laid by fitting the tongue into the groove of the boards already laid. The boards can also be fixed to timber joints by using galvanised or sherardized nails

Laying the edge trims

Fix these GRP edge trims to the boards using 13mm galvanised nails or staples. They should be fixed around the edge of the roof in a continuous line.

Preparing for lamination

If necessary, cut the fibreglass material to ensure that it fits the entire area of the roof, including any pieces needed for the corners. Use glass bandage to line the joints and fibreglass chopped strand matting to line the rest of the roof parallel to the trim, 1m at a time. A Stanley knife can be used to cut away uneven ends.


Make sure you follow the instructions on the resin container, including shaking it before use. Mix it in batches of 2kg at a time with 2% catalyst. This allows for 20 minutes to apply it before it cures. Start by laminating the joints and corners of the roof. Use a brush to apply the resin generously, starting with where the bandage will be placed. Apply the bandage, then more resin before using a roller to consolidate it. Use a paddle roller to remove any air pockets from the resin, at which point the glass should be transparent.

The topcoat

Make sure that the resin is fully dried or cured, as applying the topcoat prematurely can lead to issues like cracking and pinholes. Use sandpaper around the edges and bandages to remove any excess resin and a Stanley knife to cut excess mat away. Use a brush to apply the topcoat across the roof within 24 hours of applying the resin and bandage.

With the steps above, your GRP roof should be good to go, and your shed protected. If you’re not confident about following the steps or you to make sure that you get a professional quality GRP roof, get in touch with Gee GRP and we can easily handle it for you.

Find out What a Fibreglass Roof Is in another article we have written.

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