GRP windows for UK projects

Yes. GRP (glass-reinforced plastic or glass-reinforced polymer) is the standard British term for what North America calls fiberglass or FRP. A GRP window frame is a pultruded profile made from continuous glass fiber in a thermoset resin matrix. It has thermal conductivity of approximately 0.3 W/m·K, compared with 160 for aluminum; an expansion coefficient close to that of glass; no need for steel reinforcement; and no corrosion or repainting cycle. F1 Composite supplies complete GRP window profile sets — including frames, sashes, mullions, transoms, and glazing beads — in 65, 70, 80, 90, and 140 mm frame depths. We supply either the profiles or complete factory-glazed, leak-tested window units.

With margin. Part L in England sets a maximum U-value of 1.4 W/m²·K for replacement windows and points new dwellings toward 1.2, and the Future Homes Standard is tightening the envelope further. F1's 70-series GRP frames deliver whole-window U_w of 1.1–1.3 with standard triple glazing, and the 90-series is PHI-certified at U_w 0.78 W/m²·K (Component Certificate 2491wi03) — below the Passivhaus 0.80 criterion, which no Part L tier approaches. Because the entire frame is intrinsically insulating, these values need no thermal-break inserts and no steel stiffeners that bridge heat.

Yes — this is the segment where GRP frames are strongest. The UK Passivhaus pipeline is growing, led by the social-housing and education sectors, and Scotland has moved to legislate a Passivhaus-equivalent standard for new homes. F1's 90-series GFRP-PU frame carries PHI Component Certificate 2491wi03 at U_w 0.78 W/m²·K, and the same system is installed at Qinling Station in Antarctica against a −60°C design low — the certification and the field evidence both sit below the 0.80 W/m²·K component criterion UK Passivhaus designers specify to.

Windows are construction products. EN 14351-1 type testing for air permeability, watertightness, and wind resistance supports the Declaration of Performance, and CE marking remains recognized for construction products in Great Britain while the UKCA regime evolves. We provide the required documentation for each project. GRP is a glass-fiber composite classified under HS 3925.20 or 7019, so it falls outside the metal-focused trade remedies that affect aluminum extrusions and outside the scope of the UK CBAM announced for 2027, which covers iron, steel, and aluminum. Standard UK customs duties and 20% import VAT still apply and are itemized in our DDP quote.

Standard schedule from PO: 4–6 weeks production plus 30–38 days sea freight to Felixstowe, Southampton, or London Gateway. Total PO-to-site is typically 10–14 weeks DDP, with inland delivery to London, the Midlands, the North, and Scotland from the port of entry. Urgent samples ship air freight to any major UK hub in 4–6 days at premium cost.

We offer both models. For Passivhaus and other performance-driven projects that require factory-verified airtightness, we ship complete GRP window units that are assembled, glazed, gasketed, and leak-tested, including tilt-and-turn configurations. For UK fabricators, we supply pultruded profile sets with co-extruded EPDM gaskets, corner kits, and fabrication drawings for local assembly. Architectural AAMA 2604 or 2605 powder coatings are available in any RAL color, including the anthracite and dark tones UK architects specify. GRP holds these colors without the warping risk that dark uPVC faces on south-facing elevations.