GRP windows for UK projects

Yes — GRP (glass reinforced plastic / glass reinforced polymer) is the standard British term for what North America calls fiberglass or FRP. A GRP window frame is a pultruded profile of continuous glass fibre in a thermoset resin matrix: thermal conductivity ≈ 0.3 W/m·K (aluminium is 160), an expansion coefficient close to glass, no steel reinforcement required, and no corrosion or repainting cycle. F1 Composite manufactures the complete GRP window profile set — frame, sash, mullion, transom, glazing bead — in 65/70/80/90/140 mm frame depths, and supplies 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 (air permeability, watertightness, wind resistance) backs the Declaration of Performance, and CE marking remains recognised for construction products in Great Britain while the UKCA regime evolves — we support the documentation per project. On the cost side, GRP is a glass-fibre composite classified under HS 3925.20 / 7019, so it sits outside the metal-focused trade-remedy landscape that affects aluminium extrusions, and outside the scope of the UK CBAM announced for 2027, which covers iron, steel, and aluminium. Standard UK customs duty and 20% import VAT apply and are itemized inline 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.

Both models. For Passivhaus and performance-led projects that want factory-guaranteed airtightness, we ship complete GRP window units — assembled, glazed, gasketed, and leak-tested, including tilt-and-turn configurations. For UK fabricators, we supply the pultruded profile set with co-extruded EPDM gasketing, corner kits, and fabrication drawings for local assembly. Finishes are architectural AAMA 2604/2605 powder coating in any RAL colour — including the anthracite and dark tones UK architects specify, which GRP holds without the warping risk dark uPVC carries on south-facing elevations.