The roof window is an integral part of the roof; it must be tightly connected to it and insulated. Therefore, it is important that the moisture and thermal insulation is properly installed around the frame.
Replacing roof windows is a big undertaking. You need to know which roof windows to choose and how to take care of their proper installation. What should I do if I want to change the dimensions of my windows during replacement? What criteria should be followed when choosing new roof windows? We suggest how to install the window in the roof well, how to make proper insulation and how to finish the window niche properly.
Renovation of a usable attic is an ideal opportunity to add a few roof windows where it is currently a little too dark. Later, when the attic is finished, the grief will destroy them to make holes in the slope. Thanks to a wide range of roof windows, the attics can be seen and at the same time warm in winter and cool in summer.
The choice of window model and its dimensions is important. It is good that the width of the new windows should not be larger than the distance from rafters to rafters. When planning the location of frames, remember that their lower edge should be no higher than 120 cm above the floor, while the upper one, for the convenience of a standing person, should be no lower than 205 cm.
When the roof windows are located out of reach of our hands, it is worth to equip them with an electric drive controlled by a button, remote control or smartphone.
It is also worth remembering that two, even smaller roof windows will light up the room better than one large one.
Which new roof windows to choose?
When choosing a roof window, make sure that its heat transfer coefficient Uw is not higher than 1.3 W/(m2∙K), as this is required by current regulations. In the most energy-efficient models, it is even 0.51 W/(m2∙K).
For wet rooms, such as bathrooms, let’s choose plastic or wooden roof windows, but coated with a plastic layer. They better withstand frequent contact with water than wooden frame windows.
If you want both light and more contact with the environment, think about choosing a balcony window. It is a big investment, but it is worth considering. Such a window creates a kind of a small balcony – standing by an open window; we are outside the room and have a better view of the surroundings.
Replacing roof windows
If we plan to replace roof windows or install them in a roof that we have been operating for many years, it is very important to check the condition of its structure. In case of replacing windows in the roof, there is always a risk that it will be damaged during the work and we will be doomed to its local or major renovation. Also important is the condition of the insulation and formwork of the roof slope. We can do the preliminary research ourselves, but it is worthwhile for the roof to be looked at by a professional: a construction company, building inspector or constructor. When planning to change the place of windows or increase their number, let’s try to find construction plans for the roof truss.
If the roof needs to be renovated, it is a good idea to replace or install windows until it is done. This solution will be cheaper and will give the most possibilities to change the location of the windows.
Installation of a roof window without problems
The selected team should remove the old roof window or roofing in the designated place and cut a hole in the roof structure. Then the installation battens are screwed on, keeping the distances indicated in the manual. It is worth remembering that for the installation of roof windows, you need a flashing as well as other insulation materials.
From the windows, we start the whole attic modernization. From the outside of the roof, we remove fragments of the covering. This is easiest to do when there are tiles on the roof. You can remove them by leaning out of the room.
From the inside, we rip off the finishing and insulation materials in order to get to the rafter framing in predetermined places. Also, cut out a piece of stiff sheathing with the roofing felt, or roofing foil stretched on rafters.
The hole should be wider than the roof window frame to accommodate the thermal insulation. The windows should be fixed between the adjacent rafters at a predetermined height.
After the sash is removed from the frame, mounting angles are screwed to it in the indicated places. The roof window frame should be placed in a previously prepared hole in the roof, resting the brackets on the mounting battens. Only one screw is screwed in each corner to enable subsequent levelling of the frame. Only then the sash is installed in the frame, and then the vertical gaps between the sash and the frame are checked for parallelism along the entire length. The horizontal gaps must be checked in a similar way. If the width of the gaps is correct and they are equal, the window frame is screwed on permanently. Once again, the sash is disassembled from the frame for the time of performing the machining around the window.
Is it possible to insert a larger roof window during attic renovation?
It is, of course, possible to insert a larger window than the current one during the renovation. The difficulties depend on the rafter spacing in relation to the width of the new window. Inserting a higher window, as soon as there is enough space, is much easier. For example, inserting a 78×160 window instead of 78×118 – all you have to do is cut out the battens, enlarge the mounting hole and make a new slat. If we want to insert a wider window, e.g. 114×118 instead of 78×118, the scope of work will be much larger because we have to modify the roof structure. If the new window does not fit between the rafters, so-called “replacements” should be used. It is worth to replace the window with a new one, bigger because it will provide much more natural light to our room.
Insulation of the roof window
A roof window, like any other, requires thermal and moisture insulation. For this purpose, there are special insulation products offered by the manufacturer (moisture-resistant films, insulating frames made of foamed polyethene or insulations made of polypropylene or even sheep wool) or standard insulation materials available on the market (mineral wool, vapour barrier films).
Roof windows are sealed all around so that no thermal bridge is formed along the perimeter. Another way is to insert the thermal insulation frame into the hole. The window is also connected with the external roof insulation (roofing felt, roof membrane) and with the vapour-barrier foil, fixed after the whole attic is insulated. An insulation kit is used for this purpose, which is docked to each window. From the attic side, it is a vapour-barrier flashing, and from the outside, a vapour-permeable membrane is laid and covers the window’s contact with the aluminium flashing covering.
Above the window, a drainage gutter should be installed to additionally protect it from being flooded with water coming from the roof covering leakage, condensation or melting snow.
The last stage of window insulation is the installation of the flashing. Its type is selected according to the size of the window and type of roofing. All elements of the flashing and window cladding are marked so as to facilitate the installation of individual elements.
The cavity around the roof window is usually finished with plasterboards. A properly prepared window niche should be parallel to the floor at the top and perpendicular to the floor under the window, which allows maximum illumination of the attic rooms. A window niche prepared in this way also guarantees proper circulation of warm air – if the radiator, according to the rules, is installed directly under the window. Prepared slats made of waterproof laminated panels can also be used to finish the window niche.
Replacing a roof window with a larger one
If we want to change the dimensions of roof windows during the replacement, the technical documentation of the roof structure will be extremely useful. If we do not have it, it will be necessary to examine the structure at the window and where we want to extend or extend it. It is worth remembering that in old houses, the distances between rafters and their widths can be different and very unusual.
The new roof window will be slightly longer – check under and above the window for any structural beams. Existing replacements must be replaced by new ones by installing a longer window.
The new roof window will be slightly wider – if the distance between the rafters is too short, you need to cut out sections of the rafters and insert replacements connecting the adjacent ends of the cut rafters.
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