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Install a roof window

The installation of a roof window is a building site that requires a certain know-how, including strong knowledge of roofing. Here it is necessary to deposit certain elements of the cover without weakening the supporting structure. In addition, this site requires a declaration of work and sometimes even a building permit.


Difficulty level: To book for confirmed DIYers.

Tools and materials needed:

One meter,
A pencil,
A square of carpenter,
A mason rule,
A bubble level,
A handsaw, electric or manual,
A carpenter's hammer,
A rubber mallet,
A screwdriver,
A grinder and discs adapted to the materials,
A stepladder
Non-slip protective gloves,
Protective glasses,
A dust mask,
A roof window,
Fittings adapted to the cover,
Chevrons,
Carpenter's nails,
Galvanized flat heads,
Stainless screws.

Step 1: Determine the location of the roof window

To help determine the location of the roof window, start by looking at the installation height recommended by your supplier, on average 185 to 220 cm, to be able to maneuver the handle.

Delimit the opening of a roof window

In the lower part, the height of the lighter must be at least 90 cm for a security reason.

The notice also specifies the dimensions (H x l) of the opening (to be created according to the slope of the roof, the need for lighting and the material of the cover: slate, tile flat or relief.)

It may be necessary to make a trimmer if the spacing of the rafters is less than or greater than the width of the roof window.

Delimit the opening of a roof window

Finally, do not forget that your roof window must respect the distances fixed by the town planning rules concerning the joint ownership, namely: a front view of 1.90 m or higher, and a superior or equal side view. at 60 cm.

Step 2: Prepare

The dimensions of the hopper must correspond to the width of the frame and the height of the frame, plus the thickness of the two horizontal crosspieces of the header, plus 15 to 20 cm of margin (to ensure the seal between the window and the cover). However, the width of the roof window rarely corresponds to the size of the spacing between the rafters. It is therefore often essential to create a tailor-made trimming.

To do this, start by taking landmarks by placing the outline of the hopper in pencil on the rafters. Here you will use a meter, a ruler and a spirit level to make a perfectly square drawing.

If the attic is insulated, cut the backing panel and insulation with a saw, with a suitable blade, to access the chevron and trace the marks.

Then remove by hand, one after the other all the elements of the cover that are inside. Be careful not to cut the tiles below the future window.

Cut the saws, battens or battens by hand saw, making sure to cut them all at the same level. Then, saw the rafters of the roof trying to remove as few load-bearing elements as possible.

Here, avoid cutting a structural member. If this is not possible, contact a qualified professional.

Step 3: Make and install the trimmer

The laying of the trunk

In some recent dwellings, it may happen that a trimmer is already planned in the frame. In this case, go to the next step.

Start by cutting the pieces of the trimmer in woods of the same section as those of your frame.

Attach the trimmer elements, nailing or screwing them, checking the squareness.

Then, nail these ties on the ends of the cut rafters located at the top of the hopper and on the intact rafters located at the bottom.

You will also nail a reinforcing chevron that will rely on the ties and on the cut dices.

Step 4: Prepare the installation of the window

installation of the roof window

Using a screwdriver, carefully remove the shims and laths that may surround the window.

Place the window, placing it on wedges, and open it to separate the opening of the frame. To do this, unscrew the central articulation, after having unlocked the stops.

Attention, if a small window can be installed by only one person, to handle a model of medium or large format, it is better to be two.

Step 5: Mount the chassis

Mount the frame by inserting and screwing the brackets into the grooves provided for this purpose. Attention, according to the model of window, the fixation of the frame can be done differently, in this case follow the indications of your supplier.

installation of the roof window

Step 6: Install the chassis

Place the frame at the window hopper and install the frame fixing pastes against the header or, if necessary, on very close battens. Here simply hold the frame in place, partially screwing the brackets.

If necessary, do not hesitate to add the extra battens then balance the chassis so as to distribute the load on the window hopper.

Once this is done, check that the chassis is perfectly straight with the spirit level.

Position the frame of a roof window

Attention, the chassis must not be deformed, its two diagonals must be strictly equal.

Step 7: Install the opening

Start by lifting the opening of the window with both hands with its top up.

Then slide it sideways through the frame and straighten it to be able to engage its two pins in the chassis hinges.

Install the opening of a roof window

Once the pivots are properly engaged in the hinges, tilt the door in the normal position and lock its stops and make sure it works by opening it without forcing.

If the installation suits you, you can then finish the screwing of the brackets and if necessary add brackets provided for this purpose.

If the installation does not work properly, you will have to correct the assembly by modifying the squareness of the amounts of the frame.

Step 8: Connect the window to the roof

Untie the opening of the frame by unscrewing them.

Install the water return (the flap) and secure it by nailing it on both sides of the bottom of your chassis.

With the mallet, tap the bib to take the shape of your tiles.

Then nail the two sides of the seal kit so that it covers the top of the bib.

Make the external connections of a roof window

Finally, screw the profiles and the window cover.

Step 9: Exterior finishes

Replace all the elements of the roof and then the roof. If necessary, make tile cutouts on the grinder with a dimming disc. And re-fit the dormant in the chassis.

The interior cladding of a roof window

Step 10: Interior finishes

For the interior finishes of the roof windows, there are prefabricated claddings to be installed on the perimeter. If you do not find the right dimensions, then you will have to make yourself this wooden cladding.

Measure the depth and width of the different parts on which you will make the formwork.

Put them on 15 mm thick melamine boards and cut them with a jigsaw.

Screw the formwork on the frame then mask the connection of the different boards by adding moldings or other wood sticks.


Video Instruction: How to install a Velux roof window in a slate roof at standard height