Weather seal at head / check reveal

[embra]

Seeking some advice, specifically on weather seal detail for replacement windows.  Our current units are fitted into a check reveal, with a fairly flimsy extension piece at the head to close the gap between the steel lintel and the window frame.

 

I’m trying to work out the best way to detail the weather seal at the head of our replacement units, since the current approach doesn’t seem to be effective (sealant has perished and I can see through to outside from inside at the head). I’m struggling with the best approach since setting the window frame into the check reveal means there is no solid sealing surface at the head / lintel.

 

For now I’m omitting other details to focus on the weather seal only.

 

Head

Current: Extension piece to close the gap between the steel lintel and the window frame, gunned sealant on external corner joint.

Proposal A: Bond a ~25 mm timber strip to lintel to form check at head, 20 mm wide Compriband sealing tape in same plane as jamb / reveal.

Proposal B: ~25 mm timber extension piece manufactured as part of window, 20 mm wide Compriband sealing tape in perpendicular plane as jamb / reveal (corners / transition from head to reveal may be tricky)

 

Reveal

Current: Window frame recessed into check, gunned sealant on external corner joint.

Proposal: Window frame recessed into check (25 mm overlap between frame and outer leaf), 20 mm wide Compriband sealing tape between inner face of external leaf and outer face of window frame.

 

Any advice here is greatly appreciated!

 

Sketches

 

 

Photo of existing detail