Some studies of damp buildings have shown a relationship between extent of water/mold damage and symptoms. This study compared long duration air samples for glucan and ergosterol to extent of visible mold in houses measuring also the nature of the glucans present. Both measures were highly correlated to extent of visible mold damage in the houses; ergosterol was somewhat superior. Spore counts or prevalence of Asp/Pen in Air-O-Cell samples was not related to extent of visible mold damage but the observation of hyphal fragments was more likely when mold damage was present. This indicates that rigorous assessment of mold damage is a useful measure.

Fifty‐nine houses in the small Canadian community of Wallaceburg, 39 with high levels of biologically active contaminants and 20 with low levels, were subjected to detailed field inspections: testing to determine house‐operating parameters; monitoring of indoor environmental conditions; and simulating to predict the condensation formation potential under winter conditions. It was found that low air leakage and natural ventilation were not associated with higher levels of mold growth, as measured by ergosterol concentrations and airborne viable particulates. Analyses showed that moisture sources in the houses were a more significant factor in mold levels and dust mite antigen levels than relative humidity. Mold areas visible during inspection were not a good predictor of ergosterol concentrations in dust, indicating that much of the mold growth was in hidden locations.

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Purpose The purpose of this paper is to propose a methodology for evaluating the hygrothermal performance of framed wall assemblies based on design limits. This methodology allows designers to evaluate wall assemblies based on their absolute performance rather than relative performance which is typically done for most hygrothermal analysis. Design/methodology/approach The approach in developing this methodology was to evaluate wall assemblies against three typical design loads (e.g. air leakage, construction moisture, rain penetration) and determine limits in minimum insulation ratio, maximum indoor humidity and maximum rain penetration rates. This analysis was performed at both the field area of the wall and at framing junctions such as window sills. Findings The findings in this paper shows example design limits for various wall assemblies in heating-dominated climates in North America. Design limits for wall assemblies with moisture membranes of different vapour permeance are provided for both the field area of the wall and at window sills. Discussions about the importance of 2D hygrothermal simulation and performance of vapour permeable sub-sill membranes are also provided. Originality/value This framework of hygrothermal analysis will enable designers to make better decisions when designing framed wall assemblies suitable to the local climate and interior specifications for their projects. It will also enable the development of a design tool that will allow designers to visually see the implications of certain design decisions and filter out designs that do not meet their design conditions.

Indoor relative humidity (RH) is commonly used to characterize the indoor environment for heat-air-moisture (HAM) simulations, chamber studies, analysis of monitoring data, or test hut studies of buildings without recognition that indoor RH and condensation potential depend on concurrent outdoor temperature and RH. This can lead to the use of unrealistic boundary conditions for HAM simulations and test programs, which may result in misleading conclusions. In buildings operating without mechanical dehumidification, the indoor air moisture level (vapor pressure) is directly related to the outdoor vapor pressure, moisture sources in the space, and the level of ventilation. Mathematics suggests that one can expect buildings with similar operation, occupancy, and construction, but affected by different weather conditions, to have a similar difference between indoor and outdoor vapor pressures. This paper provides a foundation for selecting appropriate and realistic boundary conditions for the design of residential buildings that are based on vapor pressure difference with the aim to eliminate any significant bias for a particular climate. The paper will present the following: (1) Discussion of current standards that provide some guidance to selecting appropriate indoor moisture levels based on vapor pressure difference; (2) Moisture balance equations will be used to show the impact of ventilation and moisture generation rates on the vapor pressure difference; (3) Monitoring data for six multi-unit residential buildings in two Canadian climates (Toronto and Vancouver) showing the relationship between the outdoor temperatures and vapor pressure difference; (4) Analysis of seasonal indoor moisture conditions and their impact on HAM modeling based on assumed indoor RH and conditions derived by a constant vapor pressure difference; and (5) Exploration of the concept that vapor pressure difference and indoor RH are limited by moisture removal on windows.