Replacing box lintel on first floor load bearing wall

[jayc89]

Hit a bit of a snafu whilst replacing our windows. When removing the wood surround from one of the windows I noticed the internal cill was bowing downwards at one corner. Turns out;

 

1) The existing internal wooden lintel isn't long enough (only rests on the brick by approx 2" or 50mm)

2) 2 courses above the wooden lintel is the remains of the old timber sash frame

3) Between the two is a mix of nothing and rubble

4) And of course, there's no angled lintel on the external side of the wall either...

 

 

From speaking with Catnic, I know that I need to replace the lot with a solid wall lintel on the external side and a box lintel behind it (internal face), but I'm worried that the remains of the old timber sash frame is reaching the top of the external wall, probably only 3x courses from the wall plate. The wall is load bearing, 2x king post trusses rest on it. 

 

Structural opening is 1200mm x 1500mm (WxH, so 1500mm box lintels needed), room width is 4.3m and height is approx 2.5m.

 

Should I be trying to support the brickwork whilst replacing the lintel and building back up, or using acrows and some lengths of timber to support the ceiling whilst I do it? 

[markc]

I would be looking to support what’s above the wall, then as you pull stuff out and find the upper masonry isn’t sound it can be pulled out and replaced without having to re jig your supports.

[jayc89]

4 minutes ago, markc said:

I would be looking to support what’s above the wall, then as you pull stuff out and find the upper masonry isn’t sound it can be pulled out and replaced without having to re jig your supports.

So a couple of Acrows and a length of timber supporting the ceiling as close to the wall as possible? 

[markc]

9 minutes ago, jayc89 said:

So a couple of Acrows and a length of timber supporting the ceiling as close to the wall as possible? 

If the king post trusses sit above the bit you are taking out then you need to support those. If it’s only ceiling above the opening then yes a couple of props and spreaders top and bottom.

[jayc89]

Turns out there’s another lintel above the one I want to replace. I assume the one I’ve just discovered is the original as it’s much bigger, I plan to leave that one in place, fit my new box lintel and build up between the two. 

[jayc89]

All sorted.

 

With the old, wood, lintel, I was able to screw the window blinds directly into it. Now there's a chunk of steel there instead, which I plan to wrap 25mm PIR around, what's the best way to refit the blinds?