Roof Domes & Windows
Velux dominates pitched roof windows. Other manufacturers include Fakro and Keylite. Each compete with windows of the same principle, which are glazed windows that fit between the rafters and can open for draughts. A top-hung window is a window that opens outwards. These will be able to be open without fear of rain coming in. There are also the centre-pivot windows which iaginate and rotate around a cenetr axis which makes it easier to clean from inside.How much you can fit is dependent on your rafter spacing. Common rafter centers are suited to standard widths so you’re probably looking at 550mm, 780mm, or 940mm wide units. Getting the width correct means you can fit between the rafters without them needing to be cut or trimmed, simplifying the structural work. Length is more variable – you can choose a window that is short or tall depending on your preference of how much light you want to let in the room and the room configuration.
Installation must be done carefully or you will get leaks. The flashing kit that goes around the window needs to be compatible with your roof covering, as there are different flashing options available for tiles, slate, and corrugated sheets. Getting overlap in the right direction so that water goes over the flashing instead of under it is key. Most roof windows come with detailed fitting instructions, and it’s one of those tasks where the instructions should be followed to the letter.
It is worth thinking about electric windows if they are going to be out of easy reach. Windows can be wired to a switch or a remote control. Some even come with rain sensors so they will close automatically if it starts to rain. There are even some solar powered windows to save you from having to run electricity to the windows if you are doing a retrofitting.
With the recent Building Regulations on thermal performance, triple glazing has become more popular. The extra pane certainly helps with heat loss, but it does add weight and cost to the window. For loft conversions where insulation is a challenge, a better U-value does help meet the regulations without having to put extra insulation around the window frame.
Domes and Flat Roof Windows
These are different from other windows as they sit on a kerb above the roof surface instead of being set back into the slope like other windows. Rooflights with double-skinned polycarbonate domes have been around for a long time on commercial builds. They even let in a lot of light. They are not very stylish and they can look pretty dated on residential homes.
Firm rooflights are the most frequent. The fact that they don’t open helps keep the design simpler while remaining weathertight. You would typically have other windows that open for ventilation, or even an opening rooflight. Some companies provide opening rooflights, and they can be manual with a pole for higher ones or electric ones with remotes.
Roof lanterns are usually the most expensive option. They are considered to be a glassed pyramid or ridge structure that sits on top of a flat roof. They provide light from various angles and replace the lights in the centre of the room. The older timber-framed lanterns have been mostly replaced by aluminium systems which are healthier for the environment and are also more cost-efficient. They also provide a better look to open planned designs in the kitchen and living areas, even though they are not as affordable.
The kerb that the rooflight will go is built from the structural deck, usually with some timber framing which is then insulated and clad over. Getting the upstand height right is important – too low and you risk pooling water, too high and it looks odd from the interior. As is standard, most manufacturers specify a min of 150mm upstand, which is usually right for standard flat roof build-ups.
Installation here is more complex than with a pitched roof window. You are cutting a flat roof and perimeter kerbing, tie in seams for the weatherproofing, and secure the unit level and sealed. Not ’DIY’ unless you really know what you are doing. Wrongs can get very right for leaks and flat roof leaks are damaging, before you even notice.