I have a similar project to the one in this thread, but in my case, a hole needs to be made for a hatch to a space under a terrace. The terrace is an extension connected to the house with a cast floor approximately 10-15 cm thick on a wall of leca with a thickness of 20 cm. The space under the terrace has a crawl height of about 80-90 cm, and we need access for pipe installation. There are no walls or other constructions on top of the floor along the wall. The wall for the intended hatch placement is along the terrace floor's and house's gable, about 100 cm from the house foundation. I can look inside through a vent opening (see image) and see that there likely was an opening at the intended location for the hatch since it seems lecablocks were added after the wall was made. The outside is plastered, so this is not visible from the outside. I was thinking of opening the hole along the old vertical joints. The masonry was done a bit oddly, so I'm considering opening directly under the floor slab to prevent the top (white) block from falling. I am thinking of making an opening 60-70 cm wide with a height corresponding to three courses plus the white block. Should I add flat steel or support it in another way? I can only work from the outside.
