Modern roof windows in pitched roofs meet high energy and visual standards. They provide more quality of living in attic apartments and serve as ventilation or as an exit beyond the natural lighting of the interiors. With daylight spots, natural lighting can also be achieved in indoor rooms.
The design of daylight openings in pitched roofs depends on the floor plan of the respective attic, but also on factors such as cardinal direction, location in the building and room function. East- or west-facing skylights are ideal: in the morning or evening, so much sunlight enters the apartment, while at the same time the sunlight on the window and thus the heat development in the room is less strong than with south-facing skylights. Pleated blinds are often sufficient as sun protection. Low-set windows optimally capture the incident light even when the sun is low.
South-facing windows have the greatest incidence of light and the room becomes pleasantly bright even in the dark winter months. However, good sun protection is essential here, e.g. through roller shutters or heat protection awnings, so that the room does not heat up too much in summer. For optimal brightness distribution, especially in larger attic spaces, it is recommended to combine roof windows oriented in different directions.
Design: Basic requirements for the necessary window sizes for sufficient lighting and ventilation of common rooms are contained in the respective state building code. As a rule, a shell dimension of the (buzzer of all) window openings of 1/8 to 1/10 of the net floor area of the room is required. In the state building codes, these windows are sometimes also referred to as necessary windows . As a technical rule, DIN 5034 contains further requirements and specifications for the supply of daylight to indoor spaces.
Roof pitch: A roof window must be suitable for the respective roof pitch. Otherwise, rainwater cannot run off unhindered and lead to moisture damage. With roof pitches < 15°, roof windows can usually only be installed with additional special measures.
If the upper edge of the windows is the same height, longer windows are required for flatter sloping roofs in order to achieve the same parapet height at the lower edge of the window. Also to ensure optimal light incidence, longer roof windows should be chosen for flatter roof pitches.
Installation height: DIN 5034-1 describes in the area of application how an acceptable line of sight to the outside and sufficient brightness with daylight can be achieved indoors. In order to ensure the best possible view of windows with sloping ceilings, the lower edge of the window should not be lower than 90 centimetres and the upper edge of the window should not be higher than approx. 200 cm . For windows that can be operated from below, the lower edge of the window should be approx. 120 cm for comfortable operation.
Flashing frame: Roof windows are particularly exposed to climatic influences. Every roof-integrated roof window must be framed with a flashing frame that seals the transition from the roof surface to the window and prevents water, snow or dust from penetrating the roof window and damaging the roof structure. The choice of the right flashing frame depends on the type of window and the roof covering. There are suitable flashing frames for every installation situation, e.g. as single or combination flashing frames, as stretcher frames, knee flashing frames, ridge or attic connections.
Inner lining: The inner lining establishes the connection between the roof window and the sloping roof on the inside. Simple finished linings are made of water-repellent and easy-care plastic, which counteracts staining caused by condensation or mould. Alternatively, cladding in dry construction with plasterboard is possible, for which the manufacturers offer installation sets tailored to the respective roof window as a substructure. Wooden cladding on this substructure is also possible.
Frames and glazing: The frames of roof windows are usually made of wood, plastic or aluminium. Roof windows are usually installed with double or triple glazing. A manufacturer has developed a PVC-U roof window with 5-fold glazing, certified by the Passive House Institute, which achieves a Uw value of 0.51 W/m²K especially for passive houses.
Sun protection: In order to counteract overheating of the attic rooms due to solar radiation, roof windows with the appropriate orientation should be equipped with external sun protection. This is offered by many manufacturers as a system component to match the respective window, e.g. in the form of roller blinds, awnings or roller shutters, some of which also take on a privacy protection or blackout function. Special sun protection glazing or internal shading are also available, but usually do not achieve the same effect as external sun protection.
If the light opening also serves as an NRA (natural smoke extraction system), it must be ensured that the shading control system is connected to the SHEV (smoke and heat extraction system) in the case of shading or blackout devices that are freely spanned above/below the light opening, so that the shading is retracted in the event of a fire in order to release the opening for the smoke vent. Not all systems are SHEV compatible.
Roof cut-out - opening dimensions: Roof windows are available in many standardised sizes, adapted to common rafter spacing. In terms of element size, there are hardly any differences between the individual manufacturers for commercially available roof windows for living spaces, but there are differences in the assortment sizes and special shapes. It is therefore advisable to find out about the exact manufacturer's range at an early stage in order to determine the exact opening sizes. The roof window dimensions are divided into:
To determine the required opening dimension, the manufacturer's specifications for the respective element must be taken into account: As a rule, the opening should be approx. 40 – 60 mm larger in width and approx. 45 mm larger in height than the nominal dimensions of the roof window.
Renovation or retrofitting: Old or defective roof windows can usually be replaced without any problems, even across manufacturers.
When installing special replacement/renovation windows, the old interior lining is retained and the cladding around the roof window is not damaged during replacement.
Especially in the course of a major roof renovation, it can also be a good idea to completely replace the roof window with new interior cladding, which leads to increased living comfort and better thermal insulation. The window dimensions can usually be slightly enlarged. For a quick replacement, it is advisable to match the size of the roof windows to the roof construction (rafter spacing), but larger windows can also be installed with correspondingly greater effort (installation of switches).
Chimney sweeping work: Pitched roof light openings can also be used as an exit for chimney sweeping work. DIN 18160-5 (Flue systems part 5: Equipment for chimney sweeping work) contains specific specifications in this regard. Openings in roof surfaces inclined up to 60° must have a clear width of ≥ 42 cm, in conjunction with a clear length (depending on the roof pitch and the design of the window sash) of ≥ 52 cm to ≥ 80 cm. In addition, DIN 18160-5 specifies further requirements, e.g. that no opening sashes may protrude into the traffic route and that a tread must be placed below the access opening.
System diversity: Roof windows can be combined in a variety of ways and there is a large selection of design variants and accessories, e.g.:
systemFire exposure from the outside: In residential buildings , roof windows, skylights and skylights are exempt from the requirements for hard roofing according to § 32 of the Model Building Code (MBO), unless the respective state building code stipulates otherwise. In all other cases where hard roofing is required, e.g. by the respective state building code or a special building ordinance, it must be checked whether the planned roof window is approved for installation in hard roofing and may be executed.
In any case, however, even in residential buildings, roof windows must be at least 1.25 m away from fire walls and from walls that are permissible in place of fire walls, if these walls are not at least 30 cm above the roof.
Further requirements can be found in the MBO (§ 32 Roofs) or the respective state building code.
Smoke extraction via roof windows: § 35 MBO prescribes the possibility of smoke extraction from necessary stairwells, "to support effective extinguishing work". To this end, either an openable window with a free cross-section ≥ 0.5 m² or an opening for smoke evacuation with a free cross-section ≥ 1 m² must be formed at the uppermost point on each above-ground floor. This opening for smoke evacuation, e.g. a skylight, must be able to be opened from the ground floor and from the top landing. In buildings of building class 5, the opening for smoke evacuation is generally mandatory, but in buildings of building classes 4 and 5, further measures may also be necessary to support the extinguishing work.
This opening for smoke evacuation is not a smoke extraction system in accordance with DIN 18232-2, but a smoke extraction system to support the extinguishing work, which is conclusively regulated by the respective state building code. In this case, the smoke extraction area is equal to the geometric opening area without a flow coefficient.
SHEV systems, which are required by special building regulations, for example, can also be implemented with the help of roof windows, which, however, require appropriate approval for this.
professional installation of the roof window is important, as incorrect installation can cause serious consequential damage as a result of leaks. Moisture penetrating the interior can lead to mold in the insulation, the window frame and the interior walls. Certified roofing or carpentry companies are often recommended by the respective manufacturers.
DIN 4108 Thermal insulation and energy saving in buildings
DIN 5034-6 Daylight indoors - Part 6: Simplified determination of appropriate dimensions of skylight openings in roof surfaces
DIN EN 14351-1 Product standard and performance characteristics
DIN 18160-5 Flue gas systems Part 5: Equipment for chimney sweeping
work DIN EN 12101-2 Smoke and heat control - Part 2: Provisions for natural smoke and heat exhaust ventilation devices
DIN EN 13984 Waterproofing membranes – Plastic and elastomer vapour barrier membranes
FVTR Fachverband Tageslicht und Rauchschutz e.V.
Source: bauwion
