<translation>Assessment of the room's daylight. The 1/10 rule is not enough.</translation>

The study addresses the assessment of the quantity and quality of daylighting in an attic room with a façade French window.
Simulations have shown that this façade window, as the only source of daylight (despite meeting the 1/10 floor area rule), does not meet the requirements of the standard.
In the simulations, you can also compare the difference in room illumination through windows of the same size using double glazing and triple glazing.

Variant 1
Variant 1 with only one lighting opening does not provide sufficient illumination in the back of the room, and daylight is not evenly distributed throughout the room. At the window, the illumination for visual activities corresponding to the minimum daylight factor requirement of 1.5% is ensured, which is sufficient for reading, writing, and similar activities, but in the back of the room, dark corners are formed where the daylight lighting factor is around 0.4%. Variant 1 does not meet the requirement of ČSN 730580-2 for the daylight factor value of a living room.

Variant 1 - with insulating double glazing, Dmin = 0.4 %, Dm = 1.1 %, Dmax = 4.4 %

Variant 1 - with insulating triple glazing, Dmin = 0.3 %, Dm = 1.0 %, Dmax = 3.8 %

Variant 1 does not meet the requirement of ČSN 73 0580-2 Daylight in residential buildings for adequate amounts of daylight and its uniformity in the assessed room.

Variant 2
Variant 2 with one vertical and one roof window appears more suitable in terms of illumination and uniformity of daylight at the comparative work plane at the level of the work desk for the functionally defined working part of the room, intended for study or administrative work, for example.

Variant 2 - with insulating double glazing, Dmin = 1.0 %, Dm = 3.4 %, Dmax = 10.7 %

Variant 2 - with insulating triple glazing, Dmin = 0.9 %, Dm = 3.0 %, Dmax = 9.3 %

Variant 3
The highest illumination and best uniformity of daylight occurs in Variant 3 with two roof windows and one vertical window. Such an illuminated room also meets the strict requirements for preschool facilities (children's day rooms, playrooms, offices), making it a suitable children's room.
In this case, it is advisable to equip the windows with external awnings or roller blinds, which will provide protection against excessive solar gains and limit overheating and glare in the room on sunny days.

Variant 3 - with insulating double glazing, Dmin = 2.2 %, Dm = 6.0 %, Dmax = 14.60 %

Variant 3 - with insulating triple glazing, Dmin = 1.9 %, Dm = 5.2 %, Dmax = 12.6 %

The assessment of daylight in the attic room was conducted using the WDLS computer program (Astra, Zlín). The daylight factor D in % was determined at points on the working plane at a height of 850 mm above the floor level in the assessed room with lighting openings proposed in three variants.
All variants were assessed for glazing of windows (including roof windows) with insulating clear double glazing, light transmission for double glazing 0.77 and triple glazing 0.67, window construction factor 0.75.

Please note
•    A façade window as the only source of daylight does not meet the standard requirement for deeper or wider attic rooms.
•    When using triple glazing, we must not forget about its lower light transmission and propose a larger glazed area.
•    Children's rooms require higher lighting values.

Requirements for daylight in buildings

According to ČSN 730580-1:2007+Z1:2011 Daylight in buildings. Part 1. Basic requirements
Daylight in the interior of buildings and their functionally defined parts is designed based on visual activities; for visual activity class IV (reading, writing, and similar visual activities), a minimum Dmin of 1.5% and an average Dm of 5% (for upper lighting openings) are required. This standard also defines a qualitative criterion for daylight in the form of daylight uniformity. Uniformity of daylight is required in interior spaces where only the minimum daylight factor value must be satisfied. The uniformity of daylight is determined as the ratio of the smallest to the largest daylight factor in control points and must not be less than 0.2 for visual activity classes I to IV.

According to ČSN 730580-2:2007 Daylight in buildings. Part 2. Daylight in residential buildings
In residential rooms with side lighting, the daylight factor must be at least 0.7% at two control points at half the depth of the room, located 1 m from the interior surfaces of the side walls, the furthest being 3 m from the window, and the average value from both of these points must be at least 0.9%. If windows are present in two adjacent walls, it suffices for this requirement to be met in at least one of the two pairs of these control points.

According to Decree 20/2012 Coll.
1) In newly designed buildings, the lighting design in accordance with normative values must address daylight, artificial lighting, and any combined lighting, and assess them together with heating, cooling, ventilation, noise protection, sunlight exposure, including the impact of surrounding buildings and conversely the impact of the proposed building on the existing development.
(2) Residential rooms must have secured daylight in accordance with normative values.

Daylight

Daylight has been used for centuries as the main source of light in interiors and has always been an implicit part of architecture since the existence of buildings. Not only does it replace electric lighting during the day and thus reduce energy consumption; it also impacts heating and cooling, making it a significant parameter in energy-efficient design. Recent research has also shown that daylight is a great benefit for health and comfort, making it crucial for the occupants of the building.
The evaluation was developed by the Faculty of Civil Engineering, CTU in Brno.