Team Works

Tertiary shading: blinds, brise-soleil, technical curtains

Q: What solar factor g should you target on a south facade?

On a tertiary south facade, we target a solar factor g

On a south-west facade fitted with solar control glazing alone, your occupants still endure 30% of solar gains at peak summer, and your chillers run at full load from 2 PM. An exterior ZIP blind (g<=0.15, wind resistance class 4) divides these gains by 5, whereas glazing alone divides them only by 3: the thermal trade-off is decided before the glass, not after. At Kytom, our experience on diagnosed tertiary buildings shows that exterior protection becomes essential on south and west facades to stay on the tertiary decree trajectory (-40% final energy consumption by 2030) without oversizing cooling production. We handle the shading scope as a full thermal lot in its own right: calculation of the target solar factor g by orientation, selection of the wind resistance class suited to the exposure, BMS integration on KNX, DALI or BACnet bus, and joinery/electrical/HVAC coordination to neutralise conflicts with acoustic ceilings, supply diffusers and IT 246 smoke extraction vents.

Since 2006, our teams have steered these trade-offs on the projects we deliver each year. Here is the method, the technical trade-offs and the measured gains.

The regulatory framework

Solar factor g between 0.10 and 0.30 depending on orientation: the trade-offs to settle when selecting the right protection

Visual comfort in tertiary offices relies on an illuminance of 300 to 500 lux per NF EN 12464-1, with glare control (UGR<=19) and management of screen reflections. Solar protections are graded across 5 levels (0 to 4) on two criteria: reduction of solar gains and glare control. Across our recent portfolio, here are the performances we measure:

Solution	g factor	Class (0 to 4)	Gain reduction
Exterior ZIP blind	<=0.15	4	75 to 85%
Fixed oriented brise-soleil	0.15 to 0.25	3	60 to 75%
Interior aluminium venetian	0.35 to 0.50	1 to 2	30 to 50%
Acoustic technical curtain	0.40 to 0.60	–	25 to 40%

In practice at Kytom, interior shading is no longer justified by default on south or west facades. An interior venetian (g 0.40) lets through 2.5 times more gains than an exterior ZIP (g 0.15): the heat has already entered the double glazing before being reflected. The regulatory framework imposes a 40% reduction in energy consumption by 2030 relative to the reference year, i.e. a base 100 brought down to 60; our field experience confirms that exterior protection has become essential on the south and west. North facades generally make do with interior anti-glare blinds, appreciably less costly per m² than exterior devices.

For the architect and thermal engineer

Integrate shading into the dynamic thermal simulation from the schematic design phase, not after

For the architect, three integration trade-offs determine the final result. The casings of exterior ZIP blinds (180 to 220 mm high) integrate into the lintel or as a projection; on an existing curtain-wall facade, the projection alters the grid and requires IRB or ABF validation in a protected zone. Fixed brise-soleil require technical approval for fixings on external wall insulation, with 12 to 25 kg/lm to be supported via chemical anchoring or structural aluminium rail. Finally, the fabric colour must imperatively be validated on a 1 m² sample in situ: the daylight rendering differs appreciably from the paper colour chart.

Your measured gains

Summer comfort restored, air conditioning eased, complaints dropping

On the floors we instrument before and after works with HVAC sub-metering, properly sized shading — exterior ZIP blinds on south-west facades in particular — helps to significantly reduce the perceived temperature in summer, ease the load on chillers and limit complaints related to thermal discomfort. Your occupants regain stable summer comfort without having to lower the HVAC setpoint.

Electricity consumption: 30 to 40% reduction in chiller consumption on the same floors. On a 1000 m² building, the annual saving can reach several euros per m²/year depending on the prevailing electricity rate, with a return on investment generally observed between 6 and 9 years on motorised exterior solutions.

Occupant tickets: field feedback shows a marked reduction in complaints relating to glare and heat. It is often this qualitative gain, more than the energy ROI, that unlocks the CAPEX decision in committee.

When motorised exterior shading is not the right answer. On a pure north facade with no grazing sun, the ROI exceeds 12 years because gains there are structurally low: we then recommend interior anti-glare blinds. On a heritage building or external wall insulation not designed for add-on casings, fixed brise-soleil or interior blinds remain the only viable options. Below 200 m² of exposed facade, centralised BMS integration loses its relevance: local DALI control suffices, and the KNX bus premium (15 to 25% of the budget) does not pay off.

Method

Facade survey
We record orientations, heights, glazing types and admissible loads on mullions. This phase lasts 1 to 2 weeks and conditions the entire downstream technical trade-off: an existing curtain-wall facade does not accept the same casings as a new external wall insulation facade.
Thermal calculation
We set the target solar factor g by orientation and launch a dynamic thermal simulation above 1000 m². Integrating shading from the schematic design phase allows cooling production to be resized downwards (15 to 25 kW avoided over 1000 m²).
Technical choices
We arbitrate fabric (200 to 400 g/m²), colour validated on a 1 m² sample in situ, 24V low-voltage or 230V motorisation, and the wind resistance class suited to the building’s height and exposure.
BMS integration
We deploy control on a KNX, DALI or BACnet bus depending on your existing infrastructure: 256 participants per KNX line, i.e. 80 to 120 blinds over 1000 m². Light sensors and an astronomical clock automate seasonal scenarios.
Installation and configuration
Installation takes place over 2 to 4 weeks, followed by seasonal fine-tuning during the month after delivery. We combine blinds, dimmable DALI LED lighting and the HVAC setpoint to generate 15 to 25% savings on cooling and lighting.

Frequently asked questions

What solar factor g should you target on a south facade?

On a tertiary south facade, we target a solar factor g<=0.15 corresponding to class 4 solar performance for mobile protections, which translates into an exterior ZIP blind or a high-performance oriented brise-soleil. Solar control glazing alone (g 0.30) is not enough to meet summer comfort without oversizing cooling production. Exterior protection sized at g<=0.15 significantly reduces the installed cooling capacity, generating substantial HVAC CAPEX savings across the entire floor.

05 — Inspirations