How replace window Catnic lintel with something much bigger

[oly]

As a part of a new orangery, I will be taking out the corner of an exisiting single-story lean-to extension, including a lintel over a 1600 window. I'm hoping to do it myself and create as little mess in the existing building as possible.

I'll prop the ceiling joists before starting anything of course.

So I want a way of taking away the old Catnic lintel and then walls without disturbing ceilings etc too much.

The existing roof joists are cross-nailed into a timber plate resting on top of some low blocks, in turn sitting on the Catnic lintel. How is best way to deal with that – if I can get to them what about cutting through the nails with a diamond blade between joists and timber plate?

The other side of corner the joists run a parallel so not so much of an issue.

Then I have to get a couple of big beams in to support the corner of the wall. Is it usually best to get them in place before taking walls away?

 

[theprinceofdarkness]

If the joists are carrying weight, as you try to cut through the nails,they will collapse and pinch the disc. Why do you want to remove the wall plate, the ends of the joist will drift about with out it. I would knock out holes every 3' in the blocks over the catnic, then put a bit of 4" X2" through each hole and use accroyd props at each end of the wood (its called an "eye"), to hold the eye and wallplate and joists up. You can see why I think the wall plate should be left in.
The slot for the new lintel must be made before its installed and the wall under the slot is only getting in the way.
Frank

 

[noseall]

Why do you want to remove the wall plate...................I think the wall plate should be left in.

Exactly what I was wondering unless the lintel is taller and clashes with the existing wall plate perhaps....?

 

[oly]

Why do you want to remove the wall plate...................I think the wall plate should be left in.

Exactly what I was wondering unless the lintel is taller and clashes with the existing wall plate perhaps....?

Yes I'm afraid the space between the window frame and the ceiling is only 130mm or so, the cavity part of the lintel goes right up to that I think.

I was also thinking to set the new beam up in the ceiling so everything finishes completely flush. I would re-consider this though if it means so much more work. I've been looking at pics of finished projects and maybe it isn't essential.