Small red building blocks

[CeeJay]

I would like to make a very small extension to my shower room which is over the entrance staircase. Still keeping the headroom over the staircase I can extend the room by about 1 metre.

The extension would mean putting the joists into the outside wall one side and going into an existing wall the other side which is built with hollow red blocks size 4cmx20cmx40 and would be about 2 high. My joists would be 4" x 2" and my query is if these red hollow blocks would be able to take the weight of the joists albeit the new extension would be only 1metre x 1metre, and would require about 3 joists.

[cabman]

Sounds like your blocks are red terra cotta.

Some are load-bearing, some are not, depends on the thickness and the quantity of the webbing.

Would it be possible to add a trimmer joist and fix into the adjacent substrates?

Difficult to picture it from your description.

[Piprob]

No. Hollow 'terra-cuit' blocks are not regarded as load bearing, and certainly not blocks of that size. Normally, to make them carry a load, metal reinforcing rods are dropped down the voids in the blocks, then packed out with wet concrete. But with blocks of that size there would be insifficient void space to accomodate it.

A wall of those blocks might 'carry' a light-weight plasterboard ceiling hung on an aluminium frame, say, but not much more.