SIA 380/4 — Electrical energy in buildings

What is SIA 380/4?

The standard SIA 380/4 — Electrical energy in buildings is published by the Swiss Society of Engineers and Architects (SIA). It is part of the SIA 380/X family of standards governing the energy performance of buildings:

• SIA 380/1 — Thermal energy in buildings
• SIA 380/2 — Heat demand for space heating
• SIA 380/3 — Heat demand for domestic hot water
• SIA 380/4 — Electrical energy (lighting, ventilation, air conditioning)

The "lighting" part of SIA 380/4 imposes limit and target values for the installed power in W/m² per room type. Unlike EN 12464-1, which sets a floor (minimum lux), SIA 380/4 sets a ceiling (maximum watts).

Legal framework in Switzerland

SIA 380/4 is referenced in:

• The cantonal regulations implementing the Energy Act (LEn)
• The MoPEC 2014 (Model energy prescriptions of the cantons)
• The specifications of public procurement
• The labels Minergie, Minergie-P, Minergie-A
• Energy certification CECB (Cantonal building energy certificate)

For a new building or major renovation in Switzerland, SIA 380/4 compliance is almost always required — implicitly via the MoPEC or explicitly via Minergie.

Target values vs limit values

The standard distinguishes two levels:

• Target value — target for an energy-ambitious building (Minergie, labels, exemplary public buildings)
• Limit value — maximum ceiling not to be exceeded, acceptable for a standard building

As a general rule, the limit value is 30 to 50% higher than the target value.

Values by room type

The exact values must be confirmed against the current edition of the standard (available at www.sia.ch). The 2017 edition was updated in 2022 with slightly stricter values.

Calculation method

For each room, verification takes 3 steps:

1. Calculate the installed power : sum of luminaire nominal powers / room area = W/m²
2. Apply the correction factors :
   • Manual control: coefficient 1.0 (no reduction)
   • Presence detector: coefficient 0,7 to 0,9 (depending on zone)
   • Automatic dimming with daylight: coefficient 0.7 to 0.8
   • Both combined: coefficient 0,5 to 0,7
3. Compare against the SIA 380/4 target/limit value according to the room type

Formula

P_spec = (Σ P_luminaires × k_correction) / S P_spec = specific power (W/m²) P_lum = electrical power of one luminaire (W) k_corr = reduction coefficient (controls, dimming, daylight) S = usable floor area of the room (m²) Compliance: P_spec ≤ SIA_380/4_limit_value

How to comply with SIA 380/4

1. Choose high-efficiency LEDs

Modern LEDs exceed 100 lm/W at entry level and reach 180+ lm/W for professional models. For the same luminous flux, a 150 lm/W luminaire consumes half as much as a 75 lm/W one. This is the number one lever to get below the target values.

2. Size to actual needs

Never oversize "to look good" or "to be on the safe side". Respect the EN 12464-1 illuminance values (no more, no less) — exceeding Ēm by 50% means doubling the installed power with no benefit.

3. Presence detection

In rooms with intermittent occupancy (corridors, sanitary facilities, meeting rooms, changing rooms, car parks), presence detectors allow a correction coefficient of 0,7 to 0,9. This is lever no. 2.

4. Daylight-based dimming

For offices along the façade or with large glazing, daylight sensors that automatically reduce the power when sunlight comes in allow a coefficient of 0.7 to 0.8. Can be combined with presence detection.

5. Smart zoning

Rather than lighting an entire open space, divide it into separately controlled zones (per window bay, per workstation cluster). Unoccupied zones stay off or heavily dimmed.

Relationship with EN 12464-1

The two standards work together, in opposite directions:

A compliant project must satisfy both at the same time. This is possible thanks to modern high-efficiency LEDs: light sufficiently (EN 12464-1) without consuming too much (SIA 380/4).

Comply with SIA 380/4 in AutoCAD with CALEP

The command CALEP of ElectroCAD Tools calculates in real time:

• The average illuminance achieved (EN 12464-1 verification)
• The installed power in W/m² (SIA 380/4 check)
• Immediate indication of whether you are within the target or limit values
• The number of luminaires needed to reach the target

The generated report can be included directly in the calculation note of a building permit file or a Minergie audit.