Translucent Wall Panels

Q: What is the best polycarbonate thickness for a wall panel?

16mm twin-wall polycarbonate (U=1.9 W/m²K) is the most common choice for heated buildings. 25mm three-wall (U=1.4 W/m²K) is better where heating load is high. 35mm five-wall is used where acoustic performance matters.

Q: Why does GRP discolour over time?

GRP is susceptible to UV degradation without a UV-stable protective surface layer. Light transmission typically drops from 65% when new to below 35% after 10-15 years. Polycarbonate with co-extruded UV protection is significantly more stable.

Q: Can translucent panels be used in a composite panel wall run?

Yes, with specific framing and sealing details at the interface. Key challenges are weathertightness, differential thermal movement, and avoiding cold bridges through the aluminium carrier system.

Translucent cladding panels are used in wall runs to bring natural daylight into portal frame buildings without conventional windows. They are standard in agricultural buildings and common in industrial and light commercial buildings. The main types are polycarbonate multiwall panels (better thermal performance) and GRP flat sheets (lower cost, poorer long-term optical performance). All U-values and light transmission figures shown are indicative — verify from current manufacturer data sheets before specifying.

Polycarbonate multiwall wall panels

Manufacturer / Product	Thickness (mm)	Construction	U-value (W/m²K)	Light transmission (%)	Weight (kg/m²)	Sound reduction (dB)	Fire
Brett Martin Sunpal multiwall — wall application	16	Twin wall	1.9	72	2.3	20 dB	TP(a) rigid (16mm+)
	25	Three wall	1.4	67	3.1	22 dB
	35	Five wall	1.1	62	4	23 dB
Rodeca PC 2510 / PC 3510 profiled polycarbonate	25	Profiled twin wall	1.5	68	4	—	TP(a) rigid
Rodeca PC 2510 / PC 3510 profiled polycarbonate	35	Profiled three wall	1.2	62	5.5	—	TP(a) rigid

GRP flat translucent sheets

Material: GRP (glass-reinforced polyester) | Thickness: 1.5mm | U-value: 5.5 W/m²K | Fire: Typically Class 3 to BS 476

GRP yellows significantly over time — light transmission can drop from 65% to below 30% over 10–15 years. Polycarbonate is more UV-stable when co-extruded with UV protection layer.

Design guidance

Thermal performance gap: Translucent panels have lower U-values than adjacent insulated metal cladding. Account for the difference in Part L compliance calculations. A 16mm PC twin wall at U=1.9 W/m²K creates a significant thermal bridge against a composite wall panel at U=0.35 W/m²K.

Fire classification: TP(b) material has area restrictions under the Building Regulations. TP(a) rigid polycarbonate (16mm+ multiwall) has no area restriction for unsprinklered buildings in most use classes. Confirm with the current Approved Document B.

Orientation: North-facing translucent panels provide more consistent diffuse light with less solar gain. South-facing panels require solar control consideration.

Common questions

What are translucent wall panels used for in portal frame buildings?

Translucent wall panels replace sections of opaque metal cladding in wall runs to provide natural daylighting. In agricultural buildings they are used extensively to provide working light without relying on artificial lighting. In industrial and commercial buildings they are typically used at eaves level or in specific bays to provide diffuse daylight. They can significantly reduce energy consumption for artificial lighting, particularly on north-facing elevations where solar gain is less of a concern.

What is the best polycarbonate thickness for a wall panel?

For most heated commercial and agricultural portal frame buildings, 16mm twin-wall polycarbonate is the most common choice. It provides a reasonable U-value of 1.9 W/m²K, achieves TP(a) rigid fire classification, and balances light transmission against thermal performance. 25mm three-wall is the better choice where the building has a high heating load, as the improved U-value of 1.4 W/m²K reduces the thermal bridging penalty compared with the adjacent insulated metal cladding. 35mm five-wall is used where acoustic performance is also important.

Why does GRP discolour over time?

GRP (glass-reinforced polyester) is susceptible to UV degradation. Without a UV-stable protective surface layer, the resin matrix degrades under sunlight, causing yellowing and a reduction in light transmission — typically from around 65% when new to below 35% after 10–15 years. Some GRP products include gel coat or acrylic surface layers that slow this process. Polycarbonate with a co-extruded UV protection layer is significantly more UV-stable and maintains its light transmission for longer, which is why it is now more widely specified than GRP for new projects.

Can translucent panels be used in a composite panel wall run?

Yes, but they need specific framing and sealing details at the interface between the polycarbonate panel and the composite panel edge. Some composite panel manufacturers publish approved details for translucent panel integration. The key design challenges are weathertightness at the joint, differential thermal movement between polycarbonate and steel panels, and ensuring the aluminium carrier system for the polycarbonate does not create a significant cold bridge into the wall build-up.