Permanently tight roof windows

Procedure for permanently tight roof windows

This guide gathers our experience from years of development and cooperation with leading manufacturers of interior fittings for the permanently tight installation of roof windows using custom-fit adapter frames from The steps refer to the conventional installation of roof windows under normal conditions. In the case of special installation conditions, unusual dimensions or positions, it may be necessary to deviate from the procedure described. The graphics and special instructions in these instructions refer to installation in a vehicle based on a Mercedes Sprinter, but are valid for all panel vans. The instructions do not claim to be exhaustive and in the event of contradictions with instructions from the manufacturer of the roof window, the vehicle or legal framework conditions, please follow these or the manufacturer's instructions.

1. positioning:

With regard to the positioning of the skylight, various framework conditions must be observed, including the following:  

Legal regulations: The installation must be carried out in compliance with all legal requirements. Involve your TÜV/ Dekra inspector, who is to carry out the transfer as a motorhome, in the planning process at an early stage and observe the restrictions resulting from the specifications with regard to position, size, material, etc.

Roof window manufacturer's instructions: Follow the window manufacturer's instructions for installation to ensure safe installation.

Body guidelines: Observe the applicable installation guidelines for vehicles. The installation must comply with the requirements specified by the vehicle manufacturer. There are specific instructions and prohibitions, particularly in the event of modifications to the vehicle, such as changes to the crossbars

Roof structures: Take existing roof structures into account and ensure that the installation of the skylight does not cause any conflicts.

Crossbars: Pay attention to the position of the crossbars. In almost all cases, the positions we offer are selected so that it is not necessary to cut out the solid crossbars (marked in gray).

Possible installation positions for a 40x40 roof window in a Mercedes Sprinter

2. creating the framework conditions:

After you have received the frame, please first check whether the frame you have received corresponds to the desired position. Before you place the frame on the roof, we recommend that you clean it thoroughly in and around the desired installation position. Unfortunately, we cannot take back dirty frames if the position does not correspond to the desired position.

Due to their precise fit, the frames cannot be moved laterally or longitudinally in most cases. In a few cases, however, the frames can be positioned on the roof rotated by 180°, which may result in the cut-out not being positioned between the reinforcement bars. You should therefore also check the positioning against the product image or drawing. Also check whether the internal dimensions and especially the internal radii of the adapter frame match your roof window.

The adapter frame can then be used as an ideal guide for the roof cut-out. To do this, place the frame in the desired mounting position and mark the cut-out with a suitable pencil.

3. the roof cut-out

The next step is to make the cut-out in the roof of the vehicle. One important rule must be observed during installation - every chip that is not vacuumed or collected will later cause at least one rust spot. Careful and clean work pays off here. For this reason, opening the roof with an angle grinder should be avoided. It is better to use a jigsaw or a sheet metal nibbler. If you have a GRP high roof or similar, this is not a problem.

  1. Masking the roof: We recommend masking the roof next to the planned cut edge to protect the paintwork.
  2. Catch the chips: It is helpful to place a bag on the inside to catch the falling chips. This should not be temperature-sensitive, otherwise the chips will melt a hole in it. Thin bin liners are generally not sufficient here.
  3. Center hole: Start by drilling a center hole through the planned roof cut-out. Check again that it is positioned correctly and that there is sufficient clearance to the crossbars running inside.
  4. Drill holes in the corners: Drill sufficiently large holes in the respective corners to insert the separating tool. If the corners are not on a flat surface, select a different position along the marked cut-out.
  5. Carrying out the roof cut-out: Carry out the roof cut-out along the marked edges.
  6. Deburr the cut edges: The cut edges should be deburred after the cut-out.
  7. Preparation for screw holes: If the roof window requires additional holes for fastening with screws that go through the roof, pre-drill these and deburr them.
  8. Priming or painting: Prime or paint the cut edges to prevent rust.
  9. Drying the rust protection: Wait an appropriate amount of time to allow the applied rust protection to dry completely before proceeding to the next step.

4. permanently tight installation of the roof window with adapter frame

The next step is to install the adapter frame on the roof, followed by fixing the roof window to the adapter frame. The entire package is fixed in accordance with the roof window manufacturer's instructions. To ensure a permanently tight connection, all surfaces that come into contact with the sealant must be carefully cleaned. Ensure that all production residues and dirt are completely removed.

  1. Cleaning the contact surfaces: Thoroughly clean all surfaces that come into contact with the sealant , both on the roof and on the adapter frame. Remove any residue and dirt.
  2. Applying the sealant: Apply the sealant (we recommend Dekaseal 1512). For a 40x40cm skylight, we recommend applying roughly 1/3 of a cartridge between the roof and the adapter frame. For a 70×50 roof window, it is roughly 2/3 of a cartridge. Make sure to apply a roughly constant line of sealant in the middle.
  3. Attaching the adapter frame: Press the adapter frame onto the roof. The final pressing takes place when the window is attached.
  4. Installing the roof window: Repeat the same procedure for installing the roof window. For a 40x40cm window, approximately 1/3 of a cartridge of sealant is required; for a 70x50cm window, roughly 2/3 of a cartridge.

5. fixing the roof window

The roof window must always be fixed in accordance with the manufacturer's instructions. Simply gluing in the roof window without screwing it in is not permitted and should be avoided at all costs. Currently, two different systems have become established

  1. Fastening by clamping/screwing through the existing roof cut-out
  2. Screw connection through holes next to the actual roof cut-out

In both cases, a counter frame on the inside of the vehicle is recommended. You can also purchase this from us or make it yourself. For roof windows that exceed 50 cm in width, it is essential to use a counter frame that takes the curvature of the roof into account. If a solid frame is used in this case without taking the curvature of the roof into account, the roof, the external adapter frame and the roof window will be bent in the wrong direction by the counter frame and damage to the window or leaks will occur.

When the roof window is tightened, the generously applied sealant is partially pressed out of the sealing gap. This is desirable and can be dabbed off with itself due to the properties of the Dekaseal 1512 sealant. If sealant is squeezed out everywhere, it can be assumed that there is sufficient sealant in the entire sealing gap, thus ensuring long-term tightness.

When installing a roof window that is screwed in from the outside of the vehicle using screws, we recommend applying a generous amount of sealant to the pre-drilled holes before screwing the roof window to the inner frame using rust-proof screws of sufficient length. Observe the manufacturer's torque specifications or, if these are not specified, carefully screw the roof window to the inner frame.

6th degree

The roof window installation is completed by fitting the interior cladding in accordance with the roof window manufacturer's instructions.