I live in an area where there are a lot of multifamily apartments under construction. In the early stage of construction, the entire construction site seems to be made of reinforced concrete, except the elevator which is made of cinder blocks. Why isn’t that made of poured concrete too, and why do they seem to build the elevator shafts before everything else?
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Both CMUs (concrete masonry units, aka cement block) and poured concrete are commonly used for elevator shafts. But blocks are more versatile and “trendy” for interior walls (like elevator shafts) and poured walls are a little hardier for exterior walls.
CMUs are really popular, especially right now, because they’re very versatile and are considered visually appealing. Especially in modern multi-family apartments, the elevator shaft is often a visible part of the structure — people like the look of cement block. It’s an aesthetic 🙂
Poured walls are stronger laterally and easier to waterproof, so they’re preferable in spots that might be exposed to water and soil.
So basically — my guess is that your sample is skewed by the fact that it’s mostly modern, multi family apartment buildings. There’s probably a building company around you that likes to utilize exposed block from the elevator shafts in the overall building aesthetic design.
Fire control. The cinder blocks can’t burn and are pretty heat proof, so they make elevator shafts and stairways in lose rise buildings out of them so that there is a way to escape.
Are these low rise apartments where the cinder block elevator cores stick about 5 stories above the concrete podium? If so the final building is going to be timber or light gauge metal framing and they’re using concrete masonry shear walls around the elevators.
The advantage of CMU is it requires less equipment than concrete – concrete walls like these need formwork to form the walls, which is a whole operation and very expensive, out of proportion to the scale of these buildings.
So they use CMU walls as you have no formwork, no concrete pumping stations, no messing around with concrete truck delivery times, reduced inspection requirements, and can put the walls up much faster and more cheaply overall.
They have to build a scaffold to set the block up that high. They could set it inside the shaft, but that is much more difficult logistically (they would have a more difficult time getting the block and grout onto the scaffold in the shaft than outside). That would take more time and time is the most precious thing on a construction site. (safety, yes, but quickly please)
They have to put embeds (steel plates that the joists or beams sit on and are welded to) in the outside of the elevator shafts (and stairwells) to help support the upper floors. So they build the elevator shaft up and get the masons out of the way of the crane that will set the structural steel.
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