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Installation Guide

Component Parts of a GRP Roof

Tools and Materials

Stages of Installing a GRP roof

Stage 1 - Laying the Deck

Stage 2 - GRP Edge Trims

Stage 3 - Laminating

Stage 4 - Topcoating and Finishing

Catalyst Addition

Materials estimation chart

General Advice When Laying a GRP Roof

Overview and Datasheet


The GRP roofing Installation Manual contains practical guidance for installaing a GRP roof. It is recommended for installers to attend a training course before attempting to lay a GRP roof. COSHH data for the GRP roofing system can be here.

Product Description

GRP roofing system.

Standards Compliance

Part L Building Regulations Complicance (as of April 2006:)

For refusbished flat roofs GRP can be specified with a calculated ‘U’ value of 0.25W/m2K for (Calculated in accordance with BS EN ISO 6946)

For new build flat roofs GRP can be specified with a calculated ‘U’ value of 0.20W/m2K for (Calculated in accordance with BS EN ISO 6946)

Introduction to GRP Roofing

What is GRP?

Diamond Glass Reinforced Polyester (GRP) is a composite material made from a polyester resin which is reinforced by Chopped Strand Mat (CSM) glass fibres to form a GRP laminate.

History of GRP

GRP was discovered in the late 1940’s. It was quickly adopted during the 1950’s and 60’s for a wide number of applications where its corrosion proof properties, allied to its high strength and excellent appearance soon proved to be invaluable. Today, it has become the standard material for the construction of small craft, water tanks, processing vessels, building cladding panels and roof lights.

When used for roofing, GRP provides a completely weatherproof system without any of the problems associated with traditional roofing materials. Its unrivalled performance protects millions of square metres of roofs throughout the UK, to the extent that there are GRP roofs laid more than thirty years ago which are yet to show signs of deterioration.

While Diamond GRP roofing boasts qualities that make it the best roofing system money can buy, these qualities are dependant on how the roof is laid. A GRP roof will fail if it is laid incorrectly. The performance of the roof is therefore reliant on the installer’ ability to lay it.

Other Uses for GRP

The durability and lightweight qualities of GRP make it an ideal construction material for applications as diverse as lorry aerofoils and roofs, transport containers, micro-light body parts and automotive body panels. GRP is also used in hostile industrial settings for applications such as tanks and underground pipes. This is due to its ability to withstand high temperatures and its resistance to chemicals.

Unlike any other roofing material, GRP has properties that render it ideally suited to small craft construction. As well as being an inexpensive material, it is robust, flexible and will never corrode. A number of RNLI lifeboats are constructed completely from GRP. Lifeboats such as the Atlantic 75 are used in heavy weather for inshore rescue. GRP is also used throughout the automotive industry for after-sale body kits, body repair kits, kit cars, and body panels for production cars.

The GRP Roofing Market

GRP has been used for roofing applications for over fifty years. Technological advances in resin production and altering its material properties over the last thirty years have led to the manufacture of resins specially formulated for roofing. GRP roofing started to gain popularity in the mid eighties and now accounts for between 1-2% of the UK's roofing market covering millions of square metres of the UK’s roofs.

What is a GRP Roof?

The Diamond GRP roofing system is constructed from a single-ply GRP laminate applied in situ over 18mm OSB3 deck. The roof is finished with GRP edge trims and a coat of Diamond GRP topcoat.



Component Parts of a GRP Roof


This cross-section shows a breakdown of a typical GRP roofing installation and its component parts:


ic_01 B230 edge trim training-manual-5_ic1 ic_06 2400x600x18mm OSB3 decking
ic_02 D260 edge trim training-manual-5_ic2 ic_07 450g/m2 Chopped Strand Mat
ic_03 C100 edge trim training-manual-5_ic3 ic_08 GRP laminate (Roofing Resin reinforced by CSM)
ic_04 A200 edge trim training-manual-5_ic4 ic_09 Topcoat layer
ic_05 C1 universal external corner training-manual-5_ic5  

Most GRP roofing installations are for simple domestic flat roofs like the one shown below. Roofs like these incorporate the four most commonly used trims: A200, B230, C100 & D260. The roof shown below has been finished in a pigmented green topcoat with a non-slip aggregate finish.



ic_01 C100 Simulated lead flashing.
ic_02 The edge of this roof was masked off before the aggregate finish was applied.
ic_03 B260 raised edge trim - Used to direct the flow of water off the roof.
ic_04 C1 preformed universal external corner.
ic_05 C4 Preformed universal internal corner.
ic_06 A200 drip trim - Laid to facilitate water running off the roof.
ic_07 A slight fall is engineered into the substrate to avoid standing water.
ic_08 B260 raised edge trim.
ic_09 D260 - laminated into the substrate, remains unattached behind the C100 flashing.
ic_10 This roof is finished with a non-slip aggregate coating.
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