Lava Rock / Concrete walls for house

[Rob Tucker]

Just don't neglect the rebar and remember that lava rock is very fragile structurally. Also, heavy masonry as you describe has a high thermal mass effect which may not serve you well here depending on the altitude of your location. Upper elevations better. Lower elevations worse. I would also be careful about the heights of the walls and their lateral design. Earthquakes are serious things and the buildings structural design needs to be correct.

Best wishes.