Fibreglass Roofing glossary of terms & specifications

15 technical terms, material grades and Irish standards explained in plain English so you know exactly what is on a written quote.

Sorted A to Z for quick reference when comparing specifications.

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Key fibreglass roofing terms explained

Acetone Tool Wash and Surface Prep

Solvent used during GRP installation to clean paddle rollers and wipe down cured laminate before applying the pigmented topcoat or carrying out a keyed local repair.

B270 Raising Fillet and Drip Trim

Preformed GRP perimeter edge profile fixed at the back of the fascia and along raised kerbs to contain rainwater on the flat deck and channel it solely toward the gutter edge.

C250 Simulated Lead Flashing Trim

Preformed GRP cant-and-upstand flashing profile bedded into a 25mm masonry chase along brick or rendered abutment walls to allow the wall and deck to expand slightly without splitting.

Catalyst Hardener (MEKP 1% to 4%)

Methyl ethyl ketone peroxide liquid hardener mixed into orthophthalic or isophthalic polyester resin at 1% to 4% by volume depending on Irish ambient deck temperature (between 5C and 30C) to trigger chemical curing.

Chopped Strand Mat (CSM 450g/m2 & 600g/m2)

Emulsion-bound glass-fibre reinforcement mat saturating into wet polyester resin; 450g/m2 is standard for residential domestic roofs while 600g/m2 or twin-layer 450g/m2 is used on foot-traffic balconies.

Cold-Applied Wet-Lay Laminate

Liquid resin and glass-mat waterproofing consolidated by hand on site without gas torches, open flames or bitumen boilers, reducing fire risk beside timber fascias and attic eaves.

Consolidation Paddle Roller

Grooved steel or aluminium roller worked across wet resin-soaked CSM mat to drive out trapped air bubbles and compact the glass fibres into a dense, pinhole-free structural laminate.

D260 Roll-Edge Gutter Drip Trim

Preformed GRP eaves profile fixed along the drainage edge of the OSB3 deck so water sheds cleanly into the rainwater gutter without wicking back under the deck boards.

Dew Point and Deck Moisture Limit

Critical weather check before fibreglassing: the OSB3 deck moisture content must stay below 18% and surface temperature must sit at least 3C above the dew point so condensation does not interfere with resin cure.

Isophthalic Polyester Topcoat (Flowcoat)

UV-stabilised, wax-bearing pigmented topcoat (usually dark slate grey RAL 7015 or lead grey RAL 7043) brushed or rolled onto the cured GRP laminate to seal the surface against sunlight and standing water.

Non-Slip Quartz Gritted Balcony Finish

Kiln-dried angular silica sand or slate granules broadcast into a heavy second coat of GRP topcoat on walk-on roof terraces, dormer steps and valley walkways.

OSB3 18mm Tongue-and-Groove Decking

The only timber sheet board approved by major GRP system manufacturers for fibreglass roofing; plywood and chipboard are avoided because their surface veneers and glues resist resin absorption.

Outward-Opening Valley and Box Gutter Lining

Custom-moulded GRP trough laid into concealed parapet gutters and slate roof valleys, replacing theft-prone sheet lead with a rigid, joint-free channel.

Polyurethane Flexible GRP System

Elastomeric hybrid resin system specified when overlaying stable existing decks or details subject to higher thermal movement where standard rigid polyester resin would be too stiff.

Warm GRP Flat Roof Build-Up

Insulated deck assembly comprising a base deck, sealed vapour control layer, 120mm to 150mm foil-faced PIR insulation, an upper 18mm OSB3 T&G carrier deck, and the cured GRP laminate and topcoat.

Questions people ask

How much does a fibreglass roof cost in Ireland?

A GRP flat roof on a garage or extension costs €2,800 to €6,500, and €3,800 to €6,500 on a 30 to 40 m² kitchen extension. Laid, GRP runs €75 to €140 a m². The cost guide breaks it down.

Is GRP the same as fibreglass?

Yes. GRP is glass-reinforced polyester: glass fibre mat set in resin and finished with a coloured topcoat. Roofers use both names for the same roof.

How long does a fibreglass roof last?

25 to 35 years when it's laid on a sound deck in dry weather. See how long it lasts.

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