Rooflights: where they work well and how to choose a system

In a deep room, windows in the walls may mainly light the zone near the façade. Light from the roof reaches the parts located further from it. This matters in a workshop, hall and agricultural building. The layout should correspond to workstations and obstacles inside. A large transparent area in a random location will not ensure a good effect.

Before choosing, it is worth establishing the hours of use of the facility and the type of activities performed. Uniform light is sometimes more important than strong sun at one point. Glare and summer heating must also be taken into account. A skylight can reduce the need to use lamps during the day, but it does not replace a lighting design or the lighting needed after dark.

A point skylight concentrates the daylighting in a selected place. It is mounted on a base connected to the roof layers. Its height and method of insulation must correspond to the building envelope. A light strip allows light to be distributed over a longer section. However, it requires a planned opening, support and flashings along the entire length of the junction with the covering.

There are also transparent elements matched to selected roof panel systems. A similar rib height is not enough. The profile shape, width, closure of chambers and method of making the laps must be consistent with the solution. A roof panel with a PIR core should not be replaced with a random polycarbonate sheet without checking load-bearing capacity and details.

Light transmittance and thermal transmittance describe different properties. A bright element may provide a lot of light but have different heat losses than the surrounding insulated sandwich panel. In a heated building, the area of all daylighting elements must be included in the envelope balance. The thickness of the transparent panel alone is not sufficient to assess its properties.

Check whether the given coefficient refers to the infill or to the complete skylight with base and frame. These values are not interchangeable. The insulation around the opening is also important. An uninsulated section of the base can become a place of moisture condensation. Correct selection combines the product parameters with the interior temperature and humidity and the method of ventilating the facility.

The connection must drain water on the outer side of the roof. Laps, seals and flashings are made in the order specified for the system. A skylight may change the required minimum slope of the covering. In some solutions, a roof without openings has a different approval than a roof with daylighting. The lowest value from the general panel data sheet must not be transferred without checking.

From the interior side, the continuity of the layer restricting the flow of moist air must be maintained. An airtightness failure at the frame can cause water condensation even without a rain leak. The detail should account for thermal movement of different materials. Rigidly clamping the transparent element can be as wrong as leaving a loose, incompletely closed joint.

The rooflight is subject to snow and wind loads. Its size and support should follow from the design. Fire requirements appropriate to the building are also needed. An ordinary rooflight, roof hatch and smoke vent do not mean the same thing. An element intended to admit light does not become a smoke vent simply by adding an opening capability.

Resistance to a person falling should not be assumed on the basis of material thickness. The properties of the entire assembly must be documented. During works, openings must be protected and a designated walking route provided. Snow can obscure the boundary of the rooflight. Its position should therefore be known to the team that will later inspect or clear snow from the roof.

The rooflight requires access for inspection of seals, fixings and water drainage. A safe method of cleaning without standing on the transparent surface should be provided for. Cleaning agents must be suitable for the material. Some solvents can damage it. Soiling is not the only reason for a reduction in the amount of light, so the condition of the infill is also assessed during inspection.

When ordering, it is worth gathering the connection drawing, the parameters of the complete set and the maintenance rules. This allows not only the element but also the base, flashings and access protection to be priced. The best rooflight is matched to the way the building operates. It does not have to occupy the largest possible part of the roof to clearly improve conditions inside.