Q: In an insulated masonry bearing wall with parapets, the masonry walls of the backup extend above the roof. Since the rigid insulation on the roof deck stops at the parapet, the masonry on the roof side of the parapet continues from the interior to the exterior without a thermal break.
This would seem to cause problems with condensation since the concrete masonry exposed to the exterior will be cold in northern climates during the winter. How can a thermal break be created in the parapet?
A: Although this does create a thermal bridge, it generally is not a problem in buildings that are not humidified during cold weather, such as warehouses and many office buildings. However, many warehouses are heated using direct-fired mechanical units. Since the combustion of natural gas in direct fired mechanical units induces water vapor into the air, the air in these buildings will be humidified.
Depending on the height of the parapet, the masonry at the beam or joist pockets can become cold enough to permit condensation. If conditions are right, the condensation will generally form just below the roof deck since that area will be coldest, as shown in Figure 1.
It is very difficult to create a thermal break in the masonry. However, one relatively simple solution is to insulate the exposed face and even the top of the parapet. This places the masonry backup wall on the warm side of the insulation, as shown in Figure 2.
If the roofing goes to the underside of the coping, it is fairly easy to add insulation between the roof membrane on the roof side of the parapet and the masonry wall. By wrapping the insulation up and over the concrete masonry backup, the concrete masonry at the parapet will approach the interior temperature and condensation should not typically be a problem.