To continue installation, remove the sash from the frame once more. Don't forget to push the locking pin on each hinge. When releasing the hinges, support the sash from below, and then carefully put it aside in the attic.
It is important to ensure that the roof window is waterproof against precipitation. For this purpose, we recommended to fix a waterproof membrane collar around the frame.
Loosen the batten below the frame (or pull the nails out of it) to push the membrane layer underneath.
Starting from the bottom strip, slide the membrane under the laths and fasten / nail it to the bottom of the frame
When attaching the side strips of the membrane, check that it is well cut and tightly attached around the battens.
It is important to slide the top of the collar under the existing roof membrane and attach it in this way. If there are counter battens on the roof, you may need to remove a small section of the batten to slide the cover into place.
Cut the existing membrane above the batten to be able to slide the upper collar strip under it.
Lift the cut part of the membrane and attach the upper flange strap underneath it and to the frame. Put the existing membrane back in place and fasten it.