1.9 Daylight requirements in building codes

There are very few (or no) daylighting requirements or recommendations in existing standards and building regulations that are enforceable by law in any country.

The VELUX Group is working to have windows recognised as sources of illumination and sun provision in buildings; we are promoting healthy indoor environments and helping to reduce the electricity used for lighting. Our goal is for daylighting to be specifically mentioned and considered in building standards and regulations, together with specific performance criteria for all main living areas and activity zones of a building. Three key points that we believe should be taken into account, when daylight requirements are implemented in national legislation:

• Daylight should be used as primary light source in buildings in daytime and fulfil both our visual and nonvisual (biological) needs.
• We recommend levels of minimum 300 lux for most of the room area by meeting a target climate-based daylight factor and 500 lux for areas where productive work is performed. See section 1.7.3
• We recommend that national renovation strategies should address the importance of always improving daylight conditions when renovating a building.

The recommended prescriptive demands that compare window area with daylight factor as equally valid methods of achieving adequate daylight conditions have their limitations. As an example, a study by Aarhus School of Engineering investigated the influence of window size, placement and other parameters on the distribution of daylight in a room. The window size in the 23 different models is, in all cases, in accordance with the present (10% glass area to floor area) and future Danish demands for glass area to floor area (15%). The study compared the recommended requirements for daylight in commercial buildings – a daylight factor of 2% on the work plane (present Danish building regulations), and an average daylight factor in the room of 3% (suggested requirements in the 2020 standard).

The calculations show that if shading from external surroundings or common facade design is included, then only 9 of the 23 models meet a daylight factor of more than 2%, and only 3 models meet an average daylight factor of more than 3%, corresponding to future recommended requirements in Danish building legislation.

"The EU Workplace (Health, Safety and Welfare) Regulations (1992) requires that “Every workplace shall have suitable and sufficient lighting” and that this lighting “shall, as far as is reasonably practicable, be by natural light"

1.9.1 Building Codes

Legislation related to daylighting has historically been defined by one or more of the following criteria: window or glazing area in relation to the room area or facade area; quantity of daylight by daylight factor in a point in the room or as an average daylight factor of the room area; sunlight provision for a specific day or season; and a view to the outside environment (Boubekri, 2004):

• Requirements for windows and their glazing area in relation to room area or facade area. It is important to stress that legislation that mandates a minimum ratio of glazing area cannot be considered as daylight legislation, since it does not translate the actual daylight presence inside the room or building; it does not consider factors such as outside boundary conditions, building overhangs, permanent shading, glass configuration or transmittance.
• The quantity of indoor illumination inside a room. Levels for daylighting are generally described as preferred or recommended - either by specific illuminance (lux) levels on a workplane or by daylight factor (DF). Daylight factor is the most recognised performance indicator used to specify daylight conditions in buildings. The advantage of the DF method is that it is quick to calculate, and can be used in the early design process. It enables the validation of the quantity, uniformity and spatial distribution of diffuse daylight in rooms, giving architects and designers what they need to make informed decisions.

• The provision of sunlight and its duration. This type of legislation, usually referred to as “solar zoning legislation”, attempts to guarantee building occupants access to sunlight for a predetermined period of time during the day, season and year. Considerations of sunlight access and its duration will influence the decision on orientation, the disposition of rooms and their windows, selection of solar shading devices and consideration of the surroundings. In countries such as Japan and China, solar zoning relates to public health, safety and welfare.
• A view to the outside environment provides buildings' occupants with information about orientation, and weather and times changes throughout the day. This kind of legislation calls attention to window sill-height, glazing width (or the sum of widths for all windows) as a fraction of facade area, and type of glazing material used.

1.9.2 The European Committee for Standardization, CEN

In several European Standards involving daylight, the general benefits of daylight tend to be explained as follow:

• The design illuminance levels needed to enable people to perform visual tasks efficiently and accurately shall be obtained by means of daylight, electric light or a combination of both.
• Windows are strongly favoured in buildings for the daylight they deliver, and for the visual contact they provide with the outside environment. It is important to ensure windows do not cause visual or thermal discomfort, or loss of privacy.
• Potential energy savings by using daylight
• Light is important to people’s health and well-being.

In EN 12464-1:2011, the importance of daylight is taken into account and requirements for lighting are generally applicable whether it is provided by daylight, artificial lighting or a combination of both. EN 12464-1:2011 specifies requirements for most indoor work places in terms of quantity and quality of illumination. At present, only EN 15193-1 (Energy performance of buildings– Energy requirements for lighting) provides detailed considerations of the effect of daylight on the lighting energy demand (monthly and annual), and daylight availability classification as a function of the daylight factor. A new standard for daylighting of buildings that will define metrics used for the evaluation of daylighting conditions and give methods of calculation that can be applied to all spaces is under preparation.

1.9.3 The International Organization for Standardization, ISO

Several ISO working groups include daylight as an element in their work groups. At present, one standard (ISO, 2014a) applies to calculations methods for daylight in both existing buildings and the design of new and renovated buildings.

1.9.4 Design Guidelines

Several independent authorities publish guidance material and set the criteria for best practice in the profession.These are the Chartered Institution of Building Services Engineers (CIBSE), UK and the Illuminating Engineering Society of North America (IESNA), USA. As an example, CIBSE has published its Lighting Guides on Daylighting and window design, and IESNA has published a standard on approved method: IES Spatial Daylight Autonomy (SDA) and Annual Sunlight Exposure (ASE) (IESNA, 2013), which describes a new suite of metrics of daylighting performance in an existing buildings and new designs, from concept to construction documents.

Several established and much-used methods of assessing, rating, and certifying the sustainability of buildings, such as LEED (Leadership in Energy and Environmental Design), BREEAM (Building Research Establishment Environmental Assessment Methodology), and DGNB (Deutsche Gesellschaft für nachhaltiges Bauen), make recommendations for daylight as part of their assessment schemes. Overall, daylight factor is the most common indicator in most of them, but the calculation methods and benchmarks are different. Apart from daylight factor as an indicator, a view to the outside, glare control, and illuminance levels are frequently used parameters for describing visual comfort.

• BREEAM states that “. . . at least 80% of floor area in occupied spaces has an average daylight factor of 2% or more”. In domestic buildings, it states “... Kitchens achieve a minimum daylight factor of at least 2%; living rooms, dining rooms and studies achieve a minimum average daylight factor of at least 1.5%, and 80% of the working plane should receive direct light from the sky”.
• LEED states that “. . . through computer simulation that the applicable spaces achieve daylight illuminance levels of a minimum of 25 foot-candles (fc) (270 lux) and a maximum of 500 fc (5400 lux) in a clear sky condition on September 21 at 9 a.m. and 3 p.m. Areas with illuminance levels below or above the range do not comply. However, designs that incorporate view-preserving automated shades for glare control may demonstrate compliance for only the minimum 25 fc (270 lux) illuminance level".
• DGNB states that “. . . 50% of the usable area throughout a building has a DF (> 3% very good, > 2% medium, > 1% slight, < 1% none)”; “. . .based on simulation, the daylight in permanently used work areas (3%≤ DF very good, 2,5%≤ DF < 3% medium, 2% ≤ DF < 2,5% slight, DF < 2% none)