lintel type / prop from one side

[SJRSJR]

Hello

In a small shower room on the first floor of the house I currently have a tiny wood framed window (brick and a half width) that doesn't open. There's no lintel above it and it's a 300mm exterior brick cavity wall.

I'd like to put in a proper window and am told 450 is the minimum width I should aim for, which is fine. From what I've read here, 450 isn't a massive opening so I'm hoping it's not going to be too difficult,

I've had two people look at it - one says two concrete lintels on the inner an outer skin, another says a catnic lintel, so thought I'd ask here to get an idea of what's involved.

The gable end of the house is above the opening (converted loft overhead). Access from the outside is difficult because there's a pitched roof below. Inside is a timber floor.

Should it be concrete or catnic ?

And I'd like to understand how you would prop from one side? Would it be acrows and strong boys? The Strongboy website says the XL is suitable for cavity walls up to 300mm depth and 340kg workload. How do you assess the workload weight?

Appreciate any pointers. Thanks

 

[cdbe]

Post a few pictures. You wouldn't generally use a concrete on the outer skin unless it's covered with render or similar.

For that sized opening you'd probably get away without propping unless there's something bearing directly above it.

 

[SJRSJR]

Thanks. Forgot to mention that the exterior wall is rendered and I’m getting repair work done

Sorry for poor photos, scaffolding is currently in the way. The window is to the left of the bigger bedroom window and below the upstairs attic door.

I can see the external staircase is bolted nearby so I’m guessing that would limit how far a lintel would go but I think it’s well within what’s needed - 750 for a 450 opening?

Thanks

 

[cdbe]

600 for a 450 opening and this will fit in the space created by removing 3 bricks across.

 

[SJRSJR]

So is concrete just as suitable as catnic? And how would it be propped up? Thanks

 

[cdbe]

I wouldn't bother for that sized opening. If you're getting someone to do it they'll assess it but generally you could safely remove 3 bricks across without propping.

 

[^woody^]

It depends on how good your builders are.

Concrete lintels are fine, and cheaper. The bearings can be cut with a saw for minimum disruption of the wall, and no propping
The internal could if need be, be supported by a timber bolted across the face of the wall.