Raised floor building, Florida

A residential building in the hot, humid, coastal climate of Florida was constructed with a common raised bottom floor to keep it above the flood plain. Unfortunately, a combination of items makes this building a case study in the creation of moisture problems and poor pressurization.

The construction process required numerous penetrations of the raised floor to run mechanical, electrical, and structural items. This included rain leaders, chilled water, condensate, electrical, sprinklers, water and sewer. As it turned out the HVAC and envelope people did not talk to each other so no coordination was undertaken.

When completed, the air conditioned building was under negative pressure and had insulation that was problematic. It became apparent that the interior walls throughout were becoming wet and the condition was worse on lower parts indicating that this was not from roof leaks. On further investigation it was determined that warm, humid air was being pulled into the interior walls from the compromised floor beneath. That outdoor air was then condensing on the inside (cavity side) of the wallboard that was cool from exposure to the air conditioning on the other side. It didn’t take long for the partitions to begin growing mold and deteriorate the wall board to the point where vinyl wall covering was literally falling off of the walls.

Direct repair costs were very high since the problem was across the entire building. Further, there were considerable legal costs incurred to determine who was at fault and who would be paying for damages and undertaking repairs. The clear lesson learned was not to forget the bottom of the enclosure and assure that mechanical and electrical systems are integrated with the enclosure design. In particular, the critical importance of continuity of barriers including sealing of all penetrations is evident along with the need for engineers, architects, and contractors to communicate and understand the issues.

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