Mmm, waffles. They are a tasty way to build thin and strong concrete slabs that use a lot less material. They are more expensive to form than conventional flat slabs, but because of their depth, architects can design longer spans. Now Spanish architects Alarcon+Asociados have modified a waffle slab to fill it with holes so that services can be run within the depth of the slab, reducing the floor to floor height and getting some of that extra cost back. They call it Holedeck.
Waffle slabs have been around for a while; John B Parkin's brilliant and beautiful Toronto International Airport Terminal 1 was built from them. Unfortunately they are also difficult to repair; when salt got into the steel the whole thing started disintegrating. They don't have that problem in Spain.
By putting holes through the web of the waffle, the services are integrated into the depth of the slab. This permits a reduction of exterior facade per floor of 10% to 20%; the use of waffles in the first place reduces the number of columns or load bearing walls by 10-20%. It adds up to greater efficiency and energy savings. Because waffle slabs look good and break up sound reflections, you can also save on suspended ceilings.
Looking at the construction sequence in this short video, it is clear that this is not going to be cheap; there is a lot of formwork and the installation of reinforcing steel looks complicated.
Pieces are assembled progressively, alternating with the steel reinforcement setup. Once the casting molds have been laid out, the lower steel bars are assembled, followed by the windows and, finally, the upper steel bars; just as it would be done with a conventional two-way system. As for the lattice slab (with vertical borings), the upper lids of the casting molds are last placed. The assembling process is quite similar to that of any two-way voided waffle slab, with a comparable calculation and consumption of steel reinforcement.
It's an interesting idea that might make waffle slabs popular again. I am no fan of concrete as a building material, but this is a technology that uses it a lot more efficiently. More at Holedeck. Found on Dezeen.