Environmental Engineering Reference
In-Depth Information
Figure 6.7
Psychrometric chart.
Condensation can occur on any surface if its temperature is below the
dew point of the overlying air. The colder the surface, the more likely that
condensation and subsequent mold infestation will result (assuming the
surface has a sufficient nutrient base).
Condensation on interior building surfaces, within wall cavities, and
even within attic areas is relatively common in residential buildings in cli-
matic zones that require seasonal space heating. Condensation problems may
occur on or in exterior corners, at exterior wall/roof intersections, on thermal
bridges, inside wall cavities, in attic and ceiling areas, and on windows.
1. Exterior corners
Exterior corners are common locations for both condensation and mold
infestation. Exterior corners are colder than other surfaces because they are
subject to poor air circulation as well as to wind blowing through corner
assemblies (which, due to framing practices, are poorly insulated). They also
have a relatively large surface area for heat loss. Wind velocity increases as
it flows around corners. Interior surfaces will be cooled significantly if wind
enters the corner assembly and blows through it. This airflow is distinct
from infiltration.
2. Exterior wall and roof intersections
Cooler interior surfaces with the potential for condensation may occur where
exterior walls intersect roofs. There is often less ceiling insulation present,
and that which is there is often compressed, resulting in even greater heat
