Roof windows winter usage

ROOF WINDOWS WINTER USAGE

Winter conditions pose the severest test of a building’s thermal efficiency and its roof in particular. In addition to snow, driving rain, frost and the thawing process pose real challenges for roof windows. So, what can be done to limit problems such as condensation to ensure that roof windows give optimum performance in these extreme conditions?

Condensation Condensation arises from excessive humidity, inadequate ventilation and temperature variation inside and outside the building. As more heat passes to through the glazing of a roof window than through other elements of the roof, windows are particularly susceptible to it., irrespective of their manufacturer. It has therefore long been accepted that roof window manufacturers should use glazing units with a minimum U-value of 1.1 W/m2K. FAKRO windows also incorporate TGI warm spacers to reduce heat loss and thermal bridging around the glazing edge. In windows

where steel spacers are used, heat loss is considerably higher and in rooms with high humidity this may lead to heavy condensation. In extreme cases ice may even form. In winter, low temperatures also discourage home owners from providing sufficient

Ramka TGI w oknach FAKRO

Roof window performance in the winter

ventilation. With windows tightly closed, natural ventilation is often inadequate so humidity levels increase.

Methods to protect windows against formation of condensation and ice Installation Use of windows with high thermal insulation will not prevent condensation if the roof window, flashing or key components are not installed correctly. Gaps in insulation cause formation of thermal bridges as well as cold areas in and around the window.

FAKRO manufactures special installation accessories such as the XDP insulation set and Thermo flashing for improved thermal efficiency. The XDP insulation set is quick to install and highly effective, the insulation material being made from specially impregnated sheep’s wool. Its combination of density and high elasticity enables adjustment of the material to be made to suit the space being filled. A vapour permeable collar is also used to fit around the window to provide a perfect fit with the roofing underlay, protecting the insulation against moisture. The new, universal EHT-AT Thermo flashing provides additional insulation and is the ideal way to guarantee air tightness and a “warm” connection between the window and roof covering. The Thermo is applied over battens.

Another crucial factor is lininginstallation which improves insulation around the window, enhances availability of natural light and provides a consistent air flow around the window. Such linings work particularly well where a radiator is mounted beneath a window.

FAKRO roof windows can be installed at three different depths. For deeply profiled tiles the level can be raised by 3cm (N level) and a Thermo flashing used. The upper surface is then 10cm above the level of battens. Windows mounted higher than standard installation depth function better during adverse weather conditions in areas with heavy snowfalls.

+10cm

J V N

Proper ventilation Effective ventilation to remove stale, damp air will do much to protect against formation of condensation on glazing units and other surfaces.

To provide good air circulation, roof windows with an air inlet should be used. In conditions where greater levels of water vapour are generated, e.g. wet rooms additional means of ventilation and air extraction may be required.

Installation of radiators beneath a roof window Installation of radiators beneath a window is important because the flow of warm air prevents condensation on the window surface. Effectiveness of a radiator may, however, be impaired by incorrectly mounted linings or sills.

Then, circulation around the window will not be sufficient.

Cross-section of the window mounted with Thermo flashing at N depth

Proper installation of the lining and radiator under the roof window minimises risk of condensation.

Properly working natural ventilation.

Protection against accumulation of snow and ice on roof windows Roof windows are exposed to frequent changes in weather conditions.

Heavy snowfall may lead to accumulation of snow on the roof. This may be subject to changes in ambient temperature, rain, partial melting followed by re-freezing and formation of ice. To prevent ice formation, snow must regularly be removed from the roof. The lower the pitch, the greater the effects of the problem.

To ensure proper functionality of roof windows in winter care must be taken before using them. It is recommended

that leaves and all dirt should be cleaned away from the flashing at least once a year, preferably in the autumn, to ensure proper flow for rainwater.

During winter, snow and ice must be removed if possible to prevent subsequent problems as snow melts.

During winter season snow on south and west facing windows will melt naturally but on north and east facing roofs it may be present over longer periods. In such cases snow should be removed, if necessary using a specialist roofing contractor.

Fakro reserves the right to change specifications and technical parameters of products without prior notice.

K/GB/03.2015/G70A

www.fakro.com