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Old 04-18-2016, 11:23 AM
 
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Above 700 ft. or so, costs absolutely soar. So you will generally only see towers higher than that level for vanity purposes (often corporate HQ), or in a very limited number of extreme high-end markets (say Manhattan and Hong Kong).

The issue, in part, is that above that level elevator space is taking up an increasingly high proportion of the floorspace. It becomes uneconomical unless you have extreme demand from residents/office tenants or if your end user is not primarily concerned with controlling costs.
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Old 04-18-2016, 05:17 PM
 
Location: New York NY
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For high rises, building costs per sq ft are a parabola. It costs a higher amount per sq foot for the first two or three floors, but a little less per sq ft for each higher floor until you reach a point where you've minimized yr cost per sq ft. Then that cost starts to rise again because of the additional structural costs needed for a taller building. The cost per sq ft of the 80th floor is much higher than, say, the 40th floor.

The optimal height, from a cost perspective, will differ depending on local construction costs, building codes. labor costs , etc. But developers look to find that sweet spot at the bottom of the curve unless, as has been said, they are in an area where space and land are so scarce that they figure they can make their nut from rent/sales on the highest floors. It's why many new residential high-rises often try to unload the penthouses before they sell the lower floors.
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Old 04-18-2016, 07:58 PM
 
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This ^^^ plus depth to bedrock is a significant factor in the high rise equation due to heights at which caissons need to be poured for foundational work. The AIA book Nybbler refers to will have all the factors involved. Generally, a thick concrete pad can get you a certain load bearing level that can enable about 35-45 floors (depending on materials, ceiling heights, building code etc). Once you exceed that height (~500 feet depending on depth to bedrock) it becomes much more costly to build up, and due to many design imperatives for aesthetics and light - most buildings naturally will taper which leads to less useable floor plate efficiency as the service core (elevators / stairs / plumbing / hvac) and circulation becomes a greater percentage.

Last edited by ciceropolo; 04-18-2016 at 08:00 PM.. Reason: clarity
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Old 04-19-2016, 11:17 AM
 
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Quote:
Originally Posted by citylove101 View Post
For high rises, building costs per sq ft are a parabola. It costs a higher amount per sq foot for the first two or three floors, but a little less per sq ft for each higher floor until you reach a point where you've minimized yr cost per sq ft. Then that cost starts to rise again because of the additional structural costs needed for a taller building. The cost per sq ft of the 80th floor is much higher than, say, the 40th floor.

The optimal height, from a cost perspective, will differ depending on local construction costs, building codes. labor costs , etc. But developers look to find that sweet spot at the bottom of the curve unless, as has been said, they are in an area where space and land are so scarce that they figure they can make their nut from rent/sales on the highest floors. It's why many new residential high-rises often try to unload the penthouses before they sell the lower floors.
This "optimal height" issue is a huge problem in downtown San Jose. Because of the airport and the associated FAA regulations for height above MSL (See page 33 of the linked PDF), some swaths of very valuable land (ie, Diridon station area) are stuck below 10 stories, whereas most of downtown proper is limited to 27-28 stories. Local developers would love to build to 40-50 stories but they simply aren't allowed to by the FAA, making it that much harder for local projects to pencil out.
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