IWI, how to insulate timber above casement window?

[whatsthenews]

(Now added photos on my third post).So my next question is the best way to "deal with" a piece of timber infill above a window, immediately below the joists
The window is flush (casement?),so currently no sill/reveals.
There was a UPVC window/door unit in situ when we bought the house and when we started pulling the 70's wood panelling of the ceiling it became clear that the fitters had just covered the gap (presumably where there was once a course of bricks ) with interior/exterior PVC trim, with nothing but fresh air between the 2.
Our joists run parallel to the window and there certainly wasn't room for a soldier course, just the continuation of the brick course at either end.

We've recently had the window and door replaced and the installer filled the gap with rockwool and timber on the interior and PVC trim on the outside.
With the PIR boards between the joists above the window/door the timber is vertically proud of the front of the frame and interior brickwork at either end by about 25 mm
It's also horizontally proud by about 42 mm.
We'll be putting up insulated PB 62.5mm across the joists, but what's the best way to deal with this bit of timber?
Thought was that we could notch out the insulated PB so it fits around the bit of timber. This way the vertical face will have insulation across it, but the horizontal face will be left uninsulated and about 20 mm up behind the ins' PB and will be impossible to do anything with surely?
I know that when we put the wall insulation on(50mm between 75 battens,then 50mm insulated PB over the battens) we're going to create side reveals and a sill which we'll then put insulated PB on, but cannot work out how to deal with this bit of proud timber immediately above the window.

 

[oldbutnotdead]

A picture or 2 would be handy.
And one big question- what is supporting the brickwork above your window inside and out (assuming full brick or cavity walls)?

 

[whatsthenews]

Hi, there is no brickwork above the window or door. It's in a utility room at the back of the garage which is single brick with a flat roof. There's the gap which is filled with the wood and rockwool. Above this is the edge of the flat roof. The joists run parallel to the window and are let into the bricks on the perpendicular walls.
Assume that the top course of brick that's at either side used to go across the top of the window, but was removed (fell out) when they took the original wood window out 15 yrs ago ish.
Will get a photo.

 

[whatsthenews]

Photos.
Not that easy to see, but the timber is covered with the black damp proof tape which hasn't stuck properly and needs to come off anyway. Hopefully you can see that its proud of the window frame and therefore walls at either side.
Maybe before we put the insulated pb on the ceiling, we need to bury the timber in some PIR ,hence making it project further vertically and horizontally,then cut the cut out the ceiling pb around it. We've got 25 mm and 50 mm PIR boards and 37.5mm and 62.5mm insulated pb.
Obviously there's a limit to how far we can come down because of the height of the door. The finished depth of the wall at either side will be 112.5 mm, and the ceiling will be at 62.5 mm below where it is now.

 

[oldbutnotdead]

That window will look very odd once the ceiling boards are up- there'll be virtually no frame visible. Yes notch the insulation so the pb sits flush with the window- or are you battening the walls before doing the ceiling?
Or sack the wood off & replace it with more rockwool or PIR or even exp foam it it isn't doing anything structural.

 

[whatsthenews]

That window will look very odd once the ceiling boards are up- there'll be virtually no frame visible. Yes notch the insulation so the pb sits flush with the window- or are you battening the walls before doing the ceiling?
Or sack the wood off & replace it with more rockwool or PIR or even exp foam it it isn't doing anything structural.

Thanks oldbutnotdead. We were planning on putting ceiling pb up before starting the walls.
The finished ceiling will come down 20 mm below the timber. The vapour barrier level is about 42 mm above the level of the piece of timber.
We tried to "sack the wood off" before starting the roof insulation and it's well and truly wedged in the 'ole, so sadly that's not an option.

 

[oldbutnotdead]

Thanks oldbutnotdead. We were planning on putting ceiling pb up before starting the walls.
The finished ceiling will come down 20 mm below the timber. The vapour barrier level is about 42 mm above the level of the piece of timber.
We tried to "sack the wood off" before starting the roof insulation and it's well and truly wedged in the 'ole, so sadly that's not an option.

If you're fixing your wall battens to the wall your plan is fine- a head plate fixed through insulation might wobble about a bit.
Wonder what is wedging it in-rockwool wouldn't resist that much. Matey might have fixed it in i suppose, if it is solid it'll be a good anchor for that pvc frame top

 

[whatsthenews]

If you're fixing your wall battens to the wall your plan is fine- a head plate fixed through insulation might wobble about a bit.
Wonder what is wedging it in-rockwool wouldn't resist that much. Matey might have fixed it in i suppose, if it is solid it'll be a good anchor for that pvc frame top

I think it's just wedged between the top of the frame and the underside of a noggins/last joist. I didn't see him put it in. It's got a couple of screws in but even with them out it wasn't for shifting. Not sure how deep it is.Could be that he screwed the frame through it into the noggins.