Wall Assembly Modeling
Because wall and roof assemblies are becoming more complex and less tolerant to moisture, the behavior and interaction of the assembly requires close examination. This analysis requires a technical knowledge of hygrothermal processes, vapor diffusion and heat transfer – skills that typical architects aren’t trained in.
We closely examine the assembly layer by layer, providing insight into the potential condensation problems inside the wall.
Modern walls are much more hollow than those of a century ago. Newer materials, such as batt insulation and gypsum wallboard, are used. They are economical and function well, until they are faced with wetting.
Building scientists study the individual components comprising an exterior wall and their assembled interaction. If the correct materials are used, walls function as designed – they keep rain out and keep outdoor air from getting in. But when walls don’t function correctly, condensation can form within the wall. The repeated wetting of surfaces rapidly deteriorates the wall assembly and fosters mold growth.
This internal wall cavity condensation is a complicated issue--the dew point temperature inside of walls is often much greater than outdoor air dew point temperature. The sun radiates heat to wall surfaces, making them hotter than the outdoor air, and the walls absorb water from rain, creating a reservoir of moisture. This combination makes for a localized weather condition inside walls that can be drastically different and more severe than outdoor conditions.
Making matters worse, cold air from an air conditioning supply diffuser that is directed at a wall can increase the likely hood of condensation. By making the inside surface of the wall cold, the chances of condensation occurring inside the wall are greatly increased.
Qualified building envelope consultants are able to dissect a wall (or roof) assembly to determine if it was designed and constructed correctly – they even employ psychrometrics to determine whether condensation will form.
The impact of HVAC systems on the building envelope must also be considered by these consultants. If everything is properly constructed and taken into account, then your building will function optimally.
This article has mentioned several technical concepts that are more clearly defined on Psychrometrics Page 5.
| Psychrometrics Page 1 - Introduction Page 2 - Indoor Comfort Page 3 - HVAC Systems Page 4 - Building Enclosures Page 5 - Definition of Terms |