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Construction Phase Guidelines

Underfloor air distribution (UFAD) systems require good coordination between all building trades throughout the design and construction process. Shute (1995) provides an excellent list of recommendations for the design and construction of underfloor air distribution systems. McCarry (1995) also describes some guidelines based on his experiences with UFAD system installation. More recently, Bauman (2003) discusses guidelines for a well-coordinated construction sequence.  Shown below is a partial list of recommendations for design and construction.

  • It is essential that the implications of the raised access floor be considered early in the design process.
  • The concrete slab surface must be sealed to reduce dust, and the underfloor plenum and floor panels must be thoroughly cleaned both during installation of the access floor and again before occupancy.
  • The height of the access floor and the placement of the 0.6 m x 0.6 m (2 ft x 2 ft) raised floor pedestal grid is critical with respect to locating all underfloor service installations.
  • It is important to lay out underfloor equipment requiring regular maintenance to be located in accessible areas, such as corridors, not underneath furniture and partitions.
  • In partitioned office spaces, offset the partition grid from the floor grid so that partitions do not cover joints between floor panels, thereby preventing access to the underfloor plenum on both sides of the partition.
  • Consider dead load allowance and seismic bracing of the access floor.
  • Determine areas in the building with no access floor and allow for transitions to areas with access flooring.
  • In pressurized underfloor air distribution systems, greater care must be taken during construction to seal the underfloor plenum to prevent uncontrolled air leakage.
  • Designers must consider that fan rooms or access for HVAC distribution will be required at more frequent intervals than with conventional air distribution systems.
  • If called for, return air shafts must be designed between the ceiling and the underfloor plenum, usually around columns or other permanent building elements.
  • The main structural slab, the traditional working platform, will not be available continuously during construction, and therefore a well coordinated construction sequence is necessary (see Shute 1995).


Bauman, F. 2003. Underfloor air distribution (UFAD) design guide.  Atlanta: ASHRAE, Inc.

McCarry, B.T. 1995. Underfloor air distribution systems: Benefits and when to use the system in building design. ASHRAE Transactions 101 (pt. 2).

Shute, R.W. 1995. Integrated access floor HVAC: Lessons learned. ASHRAE Transactions 101 (pt. 2).

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