Making the frame watertight
Remove the sash
Remove the sash once more to continue with the installation. Remember to push in the locking pin on each hinge. Support the weight of the sash underneath whilst dislocating the hinges and carefully place back inside roof.
Cut the waterproof membrane
It is important to ensure the water tightness of a roof window against the elements. It is therefore recommended that a collar of waterproof membrane is placed around the frame. First cut the four strips that will surround the frame.
Loosen (or de-nail) the batten underneath the frame to allow for the positioning of the new collar.
Attaching the membrane
Starting with the bottom piece, slide under the batten and staple/tack to the underside of the frame.
Fixing the membrane around battens
When fixing the side pieces, make sure you cut and tightly secure around roof battens.
Fixing the top of the membrane
Fix the top piece of membrane underneath the existing roof membrane. If the roof is counter-battened, it may be necessary to remove a small section of batten in order to slide the cover piece into place.
Cut existing membrane
Cut the existing membrane over the rafter to allow the top collar piece to be slid underneath.
Overlap the membranes
Lift up the cut piece and fix the top collar piece underneath and to the frame. Replace the existing piece and fix.