More on Floor-to-Floor Height with Access Floors

The opportunity to reduce floor-to-floor height through the use of an access flooring system, as stated in the original article (EBN

Vol. 7, No. 1) but then refuted in the Editor’s Note in

Vol. 7, No. 3, is not exaggerated if you systematically think through the building. Take a six- story office building, for example. Typically, it would have a slab-on-steel structure with a 9’ ceiling, then 6” inches for lights and wiring, 2¹⁄₂” for cabling and sprinklers (with a fair amount of the sprinkler slope in the interstitial space), 14” for ducts, 19¹⁄₂” for steel, and finally 5¹⁄₂” for the slab. This gives a total floor-to-floor height of 12’ 11¹⁄₂”.

As an alternative, consider a 12” raised-floor system (for electrical, telecommunications and air distribution) with a 9’ 6” ceiling height (using suspended direct/indirect lighting), 5” for sprinklers and return air, and 10¹⁄₂” for a post-tensioned concrete structure. This system results in a total floor-to-floor height of 11’ 9¹⁄₂”. A concrete structure becomes practical with access flooring, because you no longer have to worry about poke-throughs for wiring, and no one is walking directly on the slab, so sound transmission is no longer a concern. The conventional approach would result in a building of around 77’ 9” that would be subject to high-rise building codes. The latter would produce a building around 70’ 9”, which may not trigger the high-rise code requirements —resulting in a fair amount of savings.

William Browning

Rocky Mountain Institute

Snowmass, Colorado