Case study: Community and recreation facility

A swimming pool roof at a recreation facility required dehumidification. The facility in question was built in a town located approximately 125 miles north of Toronto, Ontario, circa 2012-2013

By Chander Thusu September 7, 2022
Courtesy: IRC Building Sciences Group, a Rimkus Co.

The insulated roofing system forming the swimming pool roof comprises of the following:

  • Tongue-and-groove structural wood deck.
  • Plywood sheathing.
  • Electrical plastic junction boxes penetrating the roof structure.
  • 6 mil polyethylene vapor retarder, laps sealed with the butyl tape.
  • Two layers of polyisocyanurate insulation boards mechanically secured to roof deck.
  • Tapered crickets, as specified.
  • 60-mil thick thermoplastic polyolefin membrane mechanically secured along the spliced laps between consecutive sheets of TPO membrane.

As previously mentioned, the mechanical system responsible for the dehumidification of the high-humidity/high-temperature enclosures must be efficient, and the pool enclosure should be slightly at a negative pressure compared to the exterior air pressure. In the above referenced project, failure in the mechanical dehumidification system facilitated the egression of hot, moist air from the interior to exterior, through the roof deck and eventually to the underside of the TPO roofing membrane, where it got trapped.

Air/vapor pressure buildup underneath the TPO roofing membrane due to escaped hot, moist air resulted in the substantial billowing of the membrane, partial condensation of egressed hot, moist air and the formation of ice under sub-zero (< 0°C) temperatures. The ice, which was formed underneath the TPO membrane, was exhibiting crackling noise during walking on the membrane in the selected locations where billowing was very minimal.

Author Bio: Chander Thusu is an engineer with more than 32 years of experience. He serves as Building Sciences Practice Leader with IRC Building Sciences Group, A Rimkus Company.