Roller blinds for offices: screen fabrics, opacity, motorization
The 3% screen fabric brings the solar factor g to a value between 0.30 and 0.35.
On a south-facing office facade, the interior roller blind tops out at g_tot 0.30 (NF EN 14501:2021, annex A): below that target, it is an exterior ZIP blind or nothing. Roller blinds equip the vast majority of French office floors thanks to an 80 to 110 mm headbox compatible with 600×600 suspended ceilings. With a 3% openness screen fabric and GTB-controlled motorization, they bring the solar factor g_tot down to 0.30-0.35 on 4/16/4 double glazing, help significantly reduce air-conditioning consumption and keep screen luminance below 3000 cd/m² (EN 12464-1 threshold). Three parameters size the specification: openness factor of the screen fabric (1, 3, 5 or 10%), required opacity, control mode (manual, wired, radio, DALI/KNX/BACnet bus).
Solar protections are rated from 0 (poor) to 4 (very good) on two criteria: thermal comfort (g_tot) and visual comfort (light transmission Tv). The 3% openness interior screen fabric, PVC-coated fiberglass weave, reaches class 2 to 3 depending on the supporting glazing, with a g_tot solar factor of 0.30 to 0.35 on standard 4/16/4 double glazing (light-colored interior fabric).
The available opacities are ranked by use according to the g_tot values published in manufacturers’ technical data sheets:
- Screen 1%: outdoor view preserved, indicative g_tot 0.38-0.42, specified on north or east facades with low exposure
- Screen 3%: open space compromise, indicative g_tot 0.30-0.35, M1 or B-s2,d0 fire classification
- Screen 5 to 10%: secondary zones (cafeterias, circulation areas), indicative g_tot 0.22-0.28
- Blackout fabric 0%: video conference rooms and auditoriums, zero light transmission
Kytom contrarian position. Industry doxa specifies 3% screen by default for all orientations. Our reading differs: on a non-shaded south facade with a glazed ratio above 60%, the interior 3% screen does not hold the target. Above a targeted g_tot of 0.20, you block the view for nothing and keep overloading the air-conditioning. In this specific case, switching to an exterior ZIP represents a significant extra cost but remains technically the only answer, despite the received idea of a universal interior screen.
The screen fabric carries a 5-year manufacturer warranty on dimensional stability and color fastness, with a UV rating of 7 to 8 on the blue wool scale.
For the architect and the thermal engineer: integrating solar protection from the APS phase
The project sequencing structures survey, specification, motorization and acceptance over 6 to 10 weeks depending on the number of bays. For the architect and the thermal engineer, the real question is decided further upstream: specifying the fabric in the APS phase determines the regulatory calculation and the file.
- Laser survey: bay-by-bay measurement to within 2 mm, analysis of orientation and solar masks (neighboring buildings, balcony overhangs), survey of suspended ceiling and supporting joinery constraints
- Fabric specification: openness factor according to orientation, light color on the interior side for reflected brightness, dark color on the exterior side for solar performance, the contrast improving g_tot by 0.03 to 0.05 on reference charts
- Motorization: 24V low voltage for bays under 6 m² (32 dB motor, native DALI/KNX integration), 230V for large bays up to 12 m² (44 dB motor, dedicated GTB gateway)
- Installation and acceptance: frame fixing (angle brackets on joinery) or ceiling fixing (suspended fishplates), connection in ICTA conduit compliant with NF C 15-100, programming of time-based scenarios
For the thermal engineer, the 3% screen fabric + GTB control pairing makes it possible to integrate a dynamic g_tot into the regulatory calculation and the STD scenario (dynamic thermal simulation), which appreciably improves the DH (discomfort degree-hours) on south-west orientations, reducing the recourse to exterior brise-soleil on facades with strong architectural constraints (ABF, historic monuments, restrictive PLU zone).
Acceptance includes a report with a record of the 4 to 6 programmed scenarios (working day, midday, evening, weekend, meeting mode) and a 2-hour office manager training session on the GTB interface.
24V or 230V: technical and budget comparison for 30 blinds
The choice of motor voltage determines noise, cost and GTB integration. On a typical floor with 30 blinds, the technical and economic trade-off between 24V and 230V rests on four key criteria: sound level (24V is appreciably quieter, a decisive advantage in open space), maximum surface covered per blind, native GTB compatibility and infrastructure cost.
| Criterion | 24V low voltage motor | 230V motor |
|---|---|---|
| Operating noise | 32 dB | 44 dB |
| Maximum surface per blind | 6 m² | 12 m² |
| GTB integration | Native DALI / KNX | Dedicated gateway |
| Motor cost (excl. tax) | 180 to 250 EUR | 120 to 180 EUR |
| Infrastructure | Central transformer 400-600 EUR / zone | 230V sockets every 6 m |
24V is generally the standard on high-end office projects thanks to its quietness (32 dB vs 44 dB), the centralization of the transformer per zone of 8 to 12 blinds and its bus integration without a gateway. 230V remains relevant on full-height glazed bays or tight budgets.
The budget gap between 24V and 230V can reach several thousand euros excl. tax on a standard floor, partially offset by the air-conditioning savings linked to automatic control via light and outdoor temperature sensors.
Glare below 3000 cd/m² and 3 to 5 BREEAM Hea 01 points
Three benefits emerge from field feedback on office facades equipped with GTB-controlled motorized blinds.
Energy: the combination of 3% screen and automatic control via a luminance sensor appreciably reduces air-conditioning consumption on south-west facades, by limiting solar gains during critical hours.
Visual comfort: the luminance perceived on screen stays below the 3000 cd/m² threshold used as a reference for computer work in office environments.
Frequently asked questions
Which screen fabric openness factor should I choose according to facade orientation?
Screen 1% on north or east facades with low exposure (view preserved, g_tot 0.38-0.42). Screen 3% on south or west facades on 4/16/4 double glazing (g_tot 0.30-0.35, target reached). On a non-shaded south facade with a glazed ratio above 60%, the interior 3% screen does not hold: switch to an exterior ZIP.
24V or 230V motor for 30 blinds in open space?
For 30 blinds in an open space, the 24V low-voltage motor is often preferred for its reduced noise level (32 dB), whereas 230V remains noisier. The 24V integrates natively into DALI or KNX via a centralised transformer per zone. The 230V, cheaper to purchase, covers larger areas but requires a dedicated BMS gateway.
