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What’s with all these tower cutouts?

One question that was nagging me after seeing Hong Kong’s “typical” tower typology was: what’s with the cruciform tower plan and all these notches and cutouts? Wouldn’t it be far more efficient to square off the floor plates? I figured that it had to be in response to building regulations. I was going to mention that in this post on the typical “8-units-per-floor” tower plan, but I wanted to first understand what was going on. Thankfully a reader of this blog who is from Hong Kong was kind enough to send me a wonderfully detailed email outlining some of Hong Kong’s building regulations and how they impact the design of tall buildings.

It turns out that there are requirements for both “natural lighting and ventilation” and for “external air.” All rooms for habitation, as well as offices, bathrooms, and kitchens, are subject to these requirements. There are prescribed window areas for the “glass areas” and for the “openable areas”, both of which are a function of the room size. The glass area must equal the room area divided by 10. And the openable area must equal the room area divided by 16. I presume that these are minimum sizes because they don’t feel all that big.

For the “external air requirement”, the room must face a street no less than 4.5m in width or it must face an unobstructed space as delineated by “rectangular horizontal planes” and by “inclined planes.” The incline planes are drawn in section from the sill of the window and the angle depends on the type of room. The rectangular horizontal planes are drawn in plan and have a minimum area of 21 square meters (or ~225 square feet). If you would like to deep dive into more of the technical details you can do that here. But suffice to say that it is these requirements which are driving all of the tower notches and cutouts.

The result is tower floor plates that can look something like this:


And if we zoom into a unit (this one being a 3 bedroom apartment), you can see that both bathrooms have a window, as does the kitchen. From what I saw, there appears to be less interest in open concept floor plans. You may also finding it interesting to note some of the room dimensions (in mm) and the A/C platform sitting outside of the master bedroom. 


Finally, I should follow-up on my previous comment about tower separation distances and the ability for the above tower floor plates to be built directly adjacent to each other. Not surprisingly, this resulted in walls of towers being constructed. Ultimately this became known as the “wall effect.” So in 2011, the Sustainable Building Design (SBD) guidelines were put in place which stipulated that groups of buildings having a continuous facade length greater than 60m should comply with various separation and permeability guidelines.

So there you have it. Every market has its local nuances. The above post is a good example of that. I also love when this blog becomes a platform for two-way discussion. I learned something new today and hopefully you did too. Thank you Hiu Yeung for your emails and for providing me with all of this information.

Top image: Photo by me taken at Hong Kong’s Peak

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