The phrase House as a System, or HAAS, refers to a building science concept that takes a holistic approach to home design and performance. This concept is often referred to as a whole-house systems approach and is a way to improve home energy performance.
This concept's general idea is that one component compliments another to create an energy-efficient building system that is comfortable for its occupants. This approach is all about balance; each building component impacts the others. By understanding how your house works as a series of parts, you can be better equipped to optimize your home's performance. Projects that implement the HAAS approach at the beginning of the project will be most successful.
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By Maria Saxton, Rise Writer
Mar 19, 2025 · 5 min read
Each of these components needs to function optimally for the other elements to work favorably as well.
There are many benefits to designing, building, and occupying a home with a systems approach. The interior air quality will be improved, giving homeowners a healthy home. With a substantial building envelope and well-designed mechanical systems, a home will be more affordable to operate. In addition, your home will be more durable and have more equity. Most importantly, this approach can lower your home's environmental impact by creating a symbiotic system between the working components.
Now, let's dive into the four In a House as a System approach.
Mechanical systems consist of heating, ventilation, air conditioning, plumbing, and electrical systems. These systems regulate the indoor temperature, overall air movement, and indoor moisture levels. Heating and cooling systems should be appropriately sized for the home, and ventilation should be sufficient to protect the building and systems from moisture issues.
The environment includes the impact of conditions beyond the house, such as the house's orientation to the sun and the region's general climate. Homeowners can rarely change this component after home construction is complete, but they can influence it. For example, planting trees (increasing shade) or removing trees (increasing sun exposure) can help regulate the home's temperature without modifying the house itself.
Occupants include both the number of occupants in the home as well as their behaviors and habits that impact the home. These can include activities that increase moisture (e.g., bath/shower frequency and length) and impact temperature (e.g., preferred climate, leaving windows open, and choice in lighting). Homeowners and industry professionals can often overlook occupant behavior, yet, it is a significant energy consumption indicator, according to multiple recent studies.
Creating a tight building envelope is a significant step in improving your home's energy efficiency. You will lose less heat through the building envelope by sealing air leaks in places like your attic and around windows. To seal air leaks with a HAAS approach, you must consider ventilation. If there is a mismatch between the building envelope and ventilation systems, moisture could accumulate inside the home. This moisture can cause mold growth, condensation on windows, and insufficient air circulation.
We all know the importance of insulation to keep a home warm in the winter and cool in the summer. Rather than merely installing insulation, a HAAS approach would look at sealing the entire building envelope to optimize the insulation's performance. This approach will prevent moisture from entering the home and damaging the insulation.
An ideal heating system runs efficiently and creates a comfortable indoor environment for its occupants. However, a HAAS approach would first look at sealing the building envelope. This sealing will ensure that the specified heating system will not be oversized and thus more expensive to operate. An insulated attic or other thermal envelope failures could make the heating (and cooling) systems work harder.
Before the 1990s, asbestos was common in many household building materials, including insulation, stucco, and vinyl. Asbestos can be harmful to your health if disturbed. So always ensure you are working with an asbestos surveyor or qualified testing company when identifying and removing building materials that may contain asbestos.
Carbon monoxide is another primary consideration. This colorless, odorless gas can be produced from household appliances. It can cause health issues and even death in extreme conditions. Homes with combustion systems should always have an appropriate number of carbon monoxide detectors installed.
Mold needs to be considered with home retrofits. Mold is commonly found in any home and should be removed by a qualified professional during home retrofits.
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By understanding and emphasizing the importance of the HAAS approach throughout your entire retrofit or new construction project, each part of your home can work together to ensure ideal energy performance.
Rise Writer
Expert. Practical. Sustainable.
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Located in Roanoke, Virginia, Maria Saxton holds a Ph.D. in Environmental Design and Planning from Virginia Tech. She works as an Environmental Planner and Housing Researcher for a local firm specializing in Community Planning, Architecture, Landscape Architecture, and Historic Preservation. Her dissertation explored the environmental impacts of small-scale homes. She serves as a volunteer board member for the Tiny Home Industry Association.
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A systems approach to housing does not merely look at the building alone. Instead, it considers four main components:
The building envelope consists of the roof, walls, floors, windows, doors, insulation, and foundation. It provides a significant barrier that protects the mechanical systems and occupants. It is generally the first component considered because an effective building envelope allows for better (and often cheaper) mechanical systems and can increase their efficiency.
No, it is not! You can take a HAAS approach for well-planned home renovations to ensure the long-term success of renovation projects. The most important thing to remember is that when you retrofit one part of the home, the whole house system can be impacted.
There are three primary considerations when retrofitting a home with a HAAS approach: asbestos, carbon monoxide and combustion spillage, and mold. An ideal home retrofit balances the need to address existing issues and design to mitigate future problems.
Whether renovating or building a new home, it is essential to think of the House as a System (HAAS). The HAAS approach encourages homeowners to consider the intended or unintended consequences of building design, including energy performance, air quality, and moisture levels. This approach views the home as a series of interdependent components; every component has the potential to interact with any other.
