Can a hot tub be added to the rooftop of a townhome?

Question: Can a hot tub be added to the rooftop of a townhome? What is weight/square feet limit of these roofs.

– Water density is around 8lbs/ gallon. 
– Typical hot tub holds around 400 gallon.
– Weight of water in typical hot tub = 8 x 400 = 3200 lbs.

32000 lbs (or even 2000 lbs) is a lot of weight, and with hot tub this will a pointed weight – concentrated at one place, and for long time. Townhomes roofs are designed and constructed to act more as a roof, and not to hold so much weight.  

If a hot tub is installed, then immediately the roof won’t break but roof leak issues will start developing over time as roof membrane will start breaking. Sagging of roof will also happen with time, and edges will also start breaking causing leakage.

Looking this from weight/square feet perspective can be misleading, because the limit can vary with base area and the time for which the weight is put. 

It is difficult to say how much load roof will be able to hold as townhomes’ load bearing capacity can vary a lot and a few companies are coming up with design to hold a lot more weight with additional framing and support. A structural engineer can give exact information about a particular home you have in mind, however typical hot tub will likely have problems, and installing one on the roof isn’t a good idea. 

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