lintel over 9 inch brick wall

[brianivor]

I have a semi-integral garage, the walls within the house being two thicknesses of standard house bricks.
I would like to make a door of standard width through this wall from the hallway to the garage.
This brick wall stops at ceiling height and there are wooden joists for the first floor resting on top at right angles to the wall.
Resting on top of the joists is a 4 inch breeze block wall offset over one of the two thicknesses of bricks of the lower wall and this presumably supports the roof beams (although these are parallel to the breeze block wall.

I plan to use two 100 x 100 x 1 metre concrete lintels side by side for ease of installation and it crossed my mind that if I was to install one side at a time - that is, cut a slot of one brick thickness at a time and fully install one 100 x 100 lintel, I may not need to use external means to support the wall above the lintel, as the other "half" wall would still be supporting the joists untill the first lintel took over the job.

Do you think this would be a safe means of carrying out the work?

 

[noseall]

Do you think this would be a safe means of carrying out the work?

For a standard sized door - no problem.

It may be wise to introduce a prop for the floor joists (a length of 4" x 2" and a plank) but i can not see a great deal of downward thrust occurring unless there is a 60 stone bloke taking a bath in a jacuzzi above.