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 Whole House Ventilation Strategies
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Comprehensive Whole-House Ventilation Strategy

Most of us are familiar with the air quality index system that predicts outdoor air quality ranging from good to hazardous. The system warns those with respiratory problems to avoid outdoor exertion on bad days.

However, the Environmental Protection Agency indicates that indoor air pollutants in office buildings, public areas and homes may be two to five times, and sometimes as much as 100 times, higher than outdoor levels. This is a special concern since most people spend 90 percent of their time indoors.

Poor indoor ventilation at home can have an adverse impact on occupant health and comfort, especially for those that have greater sensitivity, such as children, the elderly and those with respiratory problems such as asthma. Inadequate ventilation can also increase the chance of moisture problems if humidity is not expelled from within, or if humid air from outside is drawn in without adequate conditioning.

Manufactured homes are required to include ventilation systems capable of continuous operation, which is unique in the homebuilding industry. Most homes built on-site rely primarily on natural ventilation via leakage through the building envelope.

In order to develop improved ventilation strategies for manufactured homes, MHRA has undertaken a course of research that will formulate a baseline for evaluating whole house ventilation and make common-sense recommendations based on solid scientific evidence.

Needle in a Haystack

The impact of airflow on building performance has traditionally been one of the most difficult phenomenons to quantify and predict.

Indoor ventilation is affected hour to hour by a myriad of complex and dynamic factors both inside and outside the home. Amongst others, these factors include wind speed, temperature, humidity levels, and homeowner activities such as bathing, cooking, and the opening and closing of doors and windows. With all of these variables, the complexity of conducting conclusive research is challenging.

It is clear that meaningful solutions do not lie in a piecemeal approach. Instead, the engineering of a whole-house ventilation system will best spur significant and cost-effective improvements.

As a first step, the MHRA Whole House Ventilation Steering Committee conducted a review of existing research to investigate existing whole-house ventilation requirements and design strategies. This review helped the committee to describe optimal design characteristics and to develop a testing protocol for further research.

Additionally, the findings of MHRA's concurrent research on manufactured homes in hot and humid climates and on attic ventilation reinforced the need for development of a comprehensive whole-house ventilation strategy. As a result, these three research projects have been brought together under a single umbrella.

New Technology, New Techniques

In the past, infiltration, or the leakage of air in and out of the house through unintended gaps, has provided a large portion of the ventilation. However, with the advent of energy-efficient building technologies and materials, homes now have a tighter envelop that limits natural ventilation. Additionally, research has shown that under certain conditions, a home can experience air pressures that increase filtration of hot and moist air into a home's wall, attic and roof cavities.

In order to maintain acceptable air quality, modern ventilation systems must be designed to supply fresh air and exhaust stale air, either by natural or mechanical means. Additionally, other activities and materials that add to indoor air pollution or excessive water vapor must also be considered in determining an acceptable whole-house ventilation solution. For example, even normal activities such as cooking, bathing, breathing and maintaining house plants can introduce excessive levels of water vapor into the home.

Practical Research

Future research will seek to establish whole-house ventilation strategies, home designs, and construction and operational parameters that result in homes that reliably maintain internally balanced air pressures, a healthy air quality and that include a mechanism to dehumidify and condition fresh air.

Out of this research, design recommendations will be made for several ventilation systems that meet the performance targets established by the Department of Housing and Urban Development (HUD). The research on the performance of manufactured home ventilation systems will enable manufacturers to make better informed decisions on design and give consumers more satisfaction with their home.

 Attic Design Strategies for Manufactured Homes
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