Feather edge over window frames, how to?

[88v8]

Outhousd, clad in 7" feather edge. Built 25 years ago.
The windows were set back flush with the 1" batten, then the feather edge lapped onto the window side and nailed to the batten, the open ends sealed onto the window frame with a non-setting paintable mastic. Which is still sticky in places.

To the north, this arrangement has survived quite well. To the west, less so, and to the south it had failed completely. The sills had rotted where they met the feather edge, also the bottom of the frame uprights.
The sun is a great destroyer.

I had thought to repeat the arrangement with the new accoya windows, but with Sikaflex 291 paintable polyurethane marine adhesive/bedding, plus the appropriate primer. As far as I can see, the wood was previously unprimed.

2" silicon bronze ship nails.

What do we think?

 

[Notch7]

Usually featheredge finishes to the outer edge of the windowframe.

Then the window has side cheeks fitted to close off the ends of the featheredge.

 

[88v8]

Ahhh, and the head?

I could bring the whole frame forward an inch, the sill would protrude 4" but never mind. I can attach it to the frame with stainless brackets and screws.
Then, thinking about it, I could put Compriband between the frame sides and the battens.
And between the frame side and the ends of the feather edge. 10mm 3/7 would do it. A separate length for each board.
And stick the feather edge to the batten with the Sikaflex, as well as the nails.

In fact, the head is near enough to the gutter that it doesn't really matter what I do there, it's not going to get wet.
But what does one usually do about the head?
And how are the side cheeks fastened to the window? Do they sit alongside the frame, or affix to the front of it?

So many ways to mess things up.

 

[Notch7]

Ahhh, and the head?

I could bring the whole frame forward an inch, the sill would protrude 4" but never mind. I can attach it to the frame with stainless brackets and screws.
Then, thinking about it, I could put Compriband between the frame sides and the battens.
And between the frame side and the ends of the feather edge. 10mm 3/7 would do it. A separate length for each board.
And stick the feather edge to the batten with the Sikaflex, as well as the nails.

In fact, the head is near enough to the gutter that it doesn't really matter what I do there, it's not going to get wet.
But what does one usually do about the head?
And how are the side cheeks fastened to the window? Do they sit alongside the frame, or affix to the front of it?

So many ways to mess things up.

Head: generally the cladding sits down a bit and the space between frame head and back of cladding trimmed out.

Side cheeks can sit alongside but usually the outer edge of the cheek is about in line with the outer edge of frame.

Typically the cladding would have vertical battens behind and the cheeks can be screwed to the battens. It depends where the window sits really.