How to install a Velux window on a sandwich panel roof

When starting a renovation or construction project, bringing in natural light is often a priority. However, the idea of cutting into a new roof sometimes raises concerns about potential heat loss or the risk of leaks. Rest assured: tile-effect sandwich panels are perfectly compatible with the installation of Velux-style roof windows.

By combining the exceptional insulation of polyurethane with the lightweight nature of steel, Isotuiles panels allow for an aesthetically pleasing and completely watertight integration. Discover how professionals successfully carry out this installation according to best practices.

The essential tools for a clean cut

Working with a sandwich panel requires a certain level of precision to avoid deforming the outer coating or damaging the insulating foam. To ensure a clean and fast cut, the choice of equipment is decisive.

Step 1: Marking and cutting the panel

Everything begins with meticulous preparation of the opening. It involves defining the exact location of the Velux, taking into account the spacing of your purlins and the layout of your sandwich panels. Once the ideal area is identified, the dimensions of the window's inner frame are marked directly onto the outer face of the panel. Always include the margin of error recommended by the manufacturer (usually 2 to 5 cm) to facilitate fitting and the installation of peripheral insulation.

To perform the cut, the safest technique is to drill each corner of the layout using your drill. These starter holes allow for easy insertion of the jigsaw blade. The cutting must be done smoothly, without jerking, to preserve the integrity of the polyurethane insulation. Immediately after this operation, a rigorous cleanup of metal shavings is required to prevent any future oxidation on your roof.

Step 2: Creating the reinforcement trimmer

Creating an opening in the roof structure requires compensating for the section of purlins or rafters that you may have cut. This is where the trimmer comes in. It is a custom-built wooden structural frame that surrounds and reinforces the opening.

In practical terms, horizontal crossbars are securely attached to connect the cut wooden components. Vertical studs are then used to close the frame. This trimmer must be perfectly level and extremely rigid, as it will support the weight of the Velux window and absorb mechanical stresses (wind, snow) transmitted through it.

Step 3: Installing and securing the roof window

Once the wooden support is finished, the actual installation can begin. The frame (the outer part of the window) is inserted into the trimmer. Before final fixation, using a spirit level is essential to check for horizontal and vertical plumb. A slight misalignment could indeed prevent the window from closing properly later on.

The frame is then securely screwed into the trimmer using the provided metal mounting brackets. All that remains is to fit the sash (the mobile glazed part) into its hinges, following the manufacturer's instructions.

Step 4: Watertightness, the key to the structure's longevity

Integrating a Velux window into Isotuiles panels requires rigorous attention to waterproofing. The exterior flashing kit (including side flashings, malleable apron, and covers) is designed to create a perfect transition between the woodwork and the relief of the metal tiles.

It is crucial to follow the direction of water flow: the panels located upstream (above the Velux) must overlap the flashing, while the lower apron of the Velux must conform to the profile of the panels located downstream. To secure the assembly, especially in the corners, adding an adhesive bituminous sealing strip between the frame and the metal sheet is a practice strongly recommended by roofing experts.