Building wall systems would work great, if it weren’t for all the holes we put in them.
One of the leading examples of these holes is caused by the packaged terminal air conditioner (PTAC), most common in hotels and multifamily buildings. PTACs are permanently installed, through-the-wall units designed to cool or heat individual rooms. Design and construction methods involving PTACs vary, but all too often, they allow water leakage into the building.
No matter what the causes of water may be, fundamental principles of wall waterproofing can be applied to PTAC installations to produce reliable and durable solutions.
Internal Water Management of PTACs
The condensate pan of the PTAC chassis can drain to the sill of the surrounding sleeve by either overtopping if condensate is excessive, or through a valve in the sill of the chassis that is activated by low temperature to prevent frost forming on coils. Water also enters the sleeve sill directly from water penetration through the louver.
Water in the sill of the sleeve is intended to drain by one of two methods: either through drain lines in the bottom of the sleeve that connect to conduits within the building that conduct the water out of the building at lower elevations, or through weep slots in the upturned front edge of the sleeve and out through the louver or louver framing system, depending on the methods of louver installation.
Inadequate Manufacturer Guidelines
Manufacturer’s instructions generally include written guidelines and schematic figures to guide installation of the wall sleeve and other PTAC components. In many cases , these instructions fail to show fundamental waterproofing components of the exterior walls and therefore fail to provide proper guidance for integrating the wall sleeve with the exterior wall waterproofing. Make sure there is proper detailing from the designer and coordination among the trades to ensure the system is effective.
A typical schematic figure (Figure 1) depicts a section through a brick veneer wall and shows, from exterior to interior: brick veneer, drainage cavity, wall sheathing, wall framing, and interior wallboard. The brick veneer above the PTAC sleeve penetration is supported by a steel lintel.
The sketch omits the water resistive barrier on the exterior sheathing, flashing on the steel lintel above the PTAC, as well as flashing beneath the PTAC – all elements that are required for reliable and durable water penetration resistance. The manufacturer’s recommended waterproofing consists solely of sealant at the perimeter of the PTAC sleeve penetration on the exterior and interior. Manufacturers generally require the wall sleeve to project beyond the outboard face of the wall from one-quarter to five-eighths of an inch. PTAC installations rely on the watertight construction of the wall sleeve to collect wind-driven rain that penetrates the exterior louver as well as condensate that drains from the condensate pan.
Some PTAC manufacturers require the wall sleeve to be pitched to the exterior; some require the wall sleeve to be installed level. Manufacturers call for flashing beneath the PTAC sleeve only where a sleeve extension is required for deep wall sections, which protects against leakage through the joint between the PTAC sleeve and sleeve extension. The flashing details typically show end dams but no upturned leg at the interior, and no slope toward the exterior.