Building Envelope

The building envelope is the physical barrier that separates the house's indoor environment from the exterior environment. Well-designed envelopes provide comfort, maintain consistent temperatures, enhance energy efficiency, and improve the home’s durability by preventing heat loss and damage from external elements like wind, rain, snow, and water. 

‍

A tight builing envelope also improves your indoor air quality and prevents the spread of flames by minimizing air leaks that would allow smoke and pollutants to infiltrate your home, resulting in a safer and healthier living environment.

Elements of the Building Envelope

• Walls
• Windows
• Roofs 
• Doors
• Floors

‍

Weatherization

‍

This is the process of increasing a home’s energy efficiency, comfortability, and safety by taking actions to protect it from the outside elements. Weatherization strengthens the building envelope by improving insulation, air seals, air quality, and energy efficiency to save money and mitigate the effects of wildfires on your home.

‍

‍

The Elements of Weatherization

1. Air Sealing/Barrier
2. Insulation
3. Ventilation
4. Moisture Control
5. Doors and Windows

‍

Thermal Bridging

Thermal bridging is one of the primary sources of heat loss in a home. A thermal bridge refers to the weak points in a building’s envelope that allow heat to transfer to surrounding materials with a higher thermal conductivity. This results in major heat losses. It is critical to minimize thermal bridging in design and construction to avoid future inefficiencies.

‍

Common Problem Areas

1. Attics
2. Crawlspaces
3. Ducts
4. Windows
5. Thermal bridges

‍

The elements of weatherization must be viewed as an integrated system where altering one element will impact all of the others, particularly in terms of condensation. 

‍

Air Sealing and Insulation

‍

Air Sealing 

Many buildings have unsealed cracks and gaps that allow air to flow out. This can greatly impact the building's comfort and energy required to regulate a home's temperature. Improving your home's air seals will decrease your home's uncontrolled airflow and reduce your energy bill.

‍

Air sealing is critical to boosting your home's performance and lowering carbon emissions. But as air seals improve, homes can't rely on natural leakage for fresh air. To combat this, implement a controlled mechanical ventilation system to maintain healthy indoor air quality. Refer to the Indoor Air Lesson for more information on improving your air quality. 

‍

Insulation

Properly insulated homes play a crucial role in maintaining consistent indoor temperatures by slowing the transfer of heat between hot and cold areas, preventing warm air from escaping in the winter, and keeping hot air out in the summer. Insulation significantly reduces your home’s reliance on HVAC systems and can lead to lower energy bills and reduced greenhouse gas emissions.

‍

Insulation efficacy is measured by an R-factor or R-value, which measures a material's resistance to heat flow. Higher values indicate better insulation properties, while lower values flag inefficiencies. 

‍

Choose insulation materials wisely and ensure a high level of continuous insulation to remove gaps and weaknesses in the building’s envelope. While spray foam can be an effective insulator and help reduce air infiltration, its high embodied carbon content should be weighed against its operational benefits. Additionally, with regular seismic activity in the area, spray foam can crack over time due to its rigidity and become less effective. Below are durable, sustainable alternatives.

‍

Sustainable Alternatives to Spray Foam: 

• Sheep’s Wool 
• Mineral Wool (made of recycled material)
• Rock Wool (made of recycled material)
• Soybean-Based Spray Foam 
• Cotton Denim Insulation

‍

An air and vapor barrier must be installed in tandem with any of the above sustainable insulation alternatives to mitigate condensation potential. Insulation is complex, and the ideal solution is often a combination of a few types to find a balance between appropriate R-factor, health, and sustainability.

‍

Cold Roof

A cold roof is a double roof with an air barrier between an internal roof and the external roof to allow for airflow. This ventilation can prevent ice dams, minimize heat loss, and prevent uneven snow melt by keeping the roof cool.

Benefits:

• energy saving in cooler climates
• prevention of ice damming, which can lead to roof leaks 
• reduction in humidity, condensation, and moisture-related problems

‍

When using any of the above sustainable insulation options, it's important to remember that the best solution is often a combination of different strategies. This is to support a balance between the right R-factor, health, and sustainability. Note that installing an air and vapor barrier is crucial to mitigating condensation potential.

Not Sure Where to Start?

Start by getting an energy audit like  Northwestern Energy’s HomeCheck. This on-site assessment will identify drafty, hot, or cold spots, and moisture issues in your home. Address these problems before moving on to home electrification.

‍

What Audit Should You Get?

What audit should you get?

When it comes to audits, it's important to consider the bigger picture. Utility-sponsored energy audits often focus on quick, low-cost measures and may not provide a comprehensive home performance assessment. If your budget allows, a more thorough energy audit can give you a comprehensive understanding of your home's energy efficiency. See our contractor list for home energy auditors that service Big Sky.

‍

Rather than relying on utility programs, find qualified, independent energy auditors through certifying bodies like the Building Performance Institute, rather than relying on utility programs. These audits often include blower door tests, which provide useful empirical data on a home's air leakage rate and are a key factor in predicting energy use and determining the right size of an HVAC system.

‍

Want to Learn More?

If you're eager to expand your knowledge, Montana State University's Weatherization Training Center offers a wealth of resources. Their virtual classes can teach you how to increase your home's energy efficiency and understand temperature control mechanisms, empowering you to make informed decisions about your home's energy use.

‍

More Resources

• Building Science Corporation: internationally recognized for its expertise in moisture dynamics, indoor air quality, and sustainable building practices.‍
• Green Building Advisor: a comprehensive source for building, designing, and remodeling green homes