GRP Roofing Hampshire

An ageing felt roof deteriorating under foot traffic indicates that the bitumen layers can no longer withstand regular use. Felt is prone to cracking under daily use, particularly on balconies or terraces where people walk frequently.

GRP roofing provides a resilient layer, forming a solid skin across the deck that endures foot traffic, hail and severe weather. A flat roof benefits from GRP when a durable, walkable finish is required for 25 to 30 years.

A balcony surface that flexes or splits during winter indicates that the covering has lost its structural integrity and can no longer accommodate thermal movement. EPDM can dent under heavy objects, whereas GRP forms a hard, seamless surface.

The cured laminate accommodates approximately 3mm of expansion per metre, managing thermal variations from hot summer surfaces to sub-zero winter lows. Movement joints absorb this expansion without causing splits.

A bay window top with a worn, cracked surface indicates that the existing covering has reached the end of its useful life. Bay window tops are among the most common GRP installation applications, alongside balconies, terraces and dormers.

GRP roofing is well suited to situations where a durable, long-term solution is required. The laminate retains its finish for 25 years or more, making it a reliable choice across a wide range of roofing applications including bay window tops.

A new extension requiring a robust flat roof benefits from a waterproof system designed to last 25 years or more without frequent maintenance. GRP installs as a continuous skin, providing a seamless, watertight barrier across the deck.

Our process involves removing the old covering, installing a new deck where necessary, and applying the laminate as a continuous skin. All new installations carry a 10-year workmanship guarantee.

A garage roof requiring longevity of 25 years or more benefits from GRP’s resistance to UV rays, hail and biological growth. A garage roof used sparingly can maintain its full 25 to 30 year lifespan without significant intervention.

Felt is prone to cracking under daily use and EPDM can dent under heavy objects, whereas GRP provides a resilient hard skin. Three elements contribute to longevity: proper deck preparation, precise detail work with double-laminated corners, and topcoat maintenance every 10 to 15 years.

We begin with a free site survey, moisture mapping the existing deck, assessing joist condition and photographing upstands. GRP requires a fresh OSB3 deck that is sanded smooth, dust-free and secured at 150mm centres.

Six common contaminants can prevent a GRP bond: bitumen residue, silicone residues, paint overspray, fungal growth, felt adhesive and mortar traces. Silicone residue can spread up to 50mm beyond visible traces, which is why we plane the top 2mm of affected areas before proceeding.

The old covering is removed down to the joists, and any weakened joists are reinforced or replaced. Fresh OSB3 boards are installed across the joists at 600mm spacing and secured at 150mm centres with screws.

Fixings are set 2mm below the surface to prevent protrusion through the laminate. All old felt, bitumen, silicone and paint must be removed before resin application to ensure the GRP system bonds correctly.

Pre-formed GRP trims are installed along eaves, verges and parapets to create clean edges and termination points. Our kit includes six detail trims: internal angle trims, external angle trims, pre-formed corner mouldings, drip edges, gutter edge trims and lead flashing replacement profiles.

Edge trims give a finished appearance and protect the laminate edges from uplift. Some conservatory junctions involve three upstands meeting at one corner, which requires each piece to be cut and stippled in stages.

Resin is applied, chopped strand mat is embedded and a second resin coat is added to create the hard skin. We typically use a 450gsm chopped strand mat with two resin coats for most domestic decks, while 600gsm reinforcement is applied for balconies and terraces.

The mat is cross-laid at 90° angles to distribute thermal stress effectively. Cross-laying prevents concentrated stress along fibre lines that can lead to hairline cracks in less rigorously installed systems.

A pigmented topcoat is applied in the desired colour to complete the surface and provide a durable finish. Walkable surfaces require an anti-slip topcoat for safety on balconies and terraces.

Curing is influenced by weather conditions. Resin sets effectively between 5°C and 25°C with humidity below 80%, which allows for rapid curing on south-facing roofs during summer, whereas shaded north slopes may require additional time. Every new installation carries a 10-year workmanship guarantee.

GRP requires a fresh OSB3 deck that is sanded smooth, dust-free and secured at 150mm centres. All old felt, bitumen, silicone and paint must be removed before resin application.

We remove the old covering down to the joists, reinforcing or replacing any weakened joists. New OSB3 sheets are fastened with screws every 150mm, with fixings set 2mm below the surface.

Six common contaminants can prevent a GRP bond:

• Bitumen residue from felt
• Silicone residues from previous repairs
• Paint overspray
• Fungal growth
• Felt adhesive
• Mortar traces from brickwork

Silicone residue can spread up to 50mm beyond visible traces, which is why we plane the top 2mm of the deck in affected areas.

Resin cures effectively between 5°C and 25°C with humidity below 80%. Cold or wet weather can delay the process. Substrate temperature is more critical than air temperature, as resin cures from the deck upward.

GRP detailing around upstands and skylights uses double-laminated corners and 450gsm reinforcement. Upstands are elevated at least 150mm above the deck, with hand-cut mat patches applied behind the main lay-up at each junction.

Flat roof leaks frequently originate at junctions, so our detail work includes three resin passes rather than two. Diagonal mat patches are placed behind the main field laminate at internal corners, with pre-formed mouldings at external corners.

Our kit includes six detail trims:

• Internal angle trims
• External angle trims
• Pre-formed corner mouldings
• Drip edges
• Gutter edge trims
• Lead flashing replacement profiles

Some conservatory junctions involve three upstands meeting at one corner, which requires each piece to be cut and stippled in stages.

Movement joints and double-laminated stress points prevent GRP from cracking across Hampshire’s varying temperatures. Cross-laid mat disperses stress, accommodating the thermal range from hot summer surfaces to sub-zero winter lows.

The laminate can expand approximately 3mm per metre across this range. Joints are placed over structural movement lines, and every fixing line and plane change is reinforced with stress patches.

Mat orientation is also important. Layers are cross-laid at 90° angles to distribute thermal stress across the membrane, preventing concentrated stress along fibre lines that can lead to hairline cracks in less rigorously installed systems.

GRP requires a minimum 1:80 fall to outlets, confirmed with a laser level at 1-metre intervals. Ponding can significantly shorten the lifespan of any flat roof.

Falls are built into flat-built extensions using tapered firring strips or tapered insulation, sloping the new deck from the high point to the outlet. A well-constructed flat roof should shed water within 30 minutes of rainfall stopping, with no puddle exceeding 5mm in depth.

Every finished roof undergoes a flood test. Outlets are blocked, the deck is filled to a 25mm depth, then unblocked and the flow is timed. Your handover report includes gradient readings, flood test results and outlet flow measurements.