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Net Zero Retrofits: It's All About the Building Envelope Part Two

Updated: Mar 26

The building envelope acts as a protective barrier that separates the inside of your home from the outside environment. It's made up of four crucial control layers: water, air, thermal, and vapor. These control layers ensure that your home is comfortable, durable, and energy-efficient.

In the first part of this blog post, we discussed the weather and air barriers. Now, let's take a closer look at the remaining two critical control layers – the thermal and vapor barriers. We'll explore their roles and significance and how they are related to the approach towards achieving a Net Zero home.


A smiling women sat on a sofa in a cosy home

Maintaining Comfort: The Thermal Barrier


A comfortable indoor temperature is essential for any home, and maintaining it requires a well-designed thermal barrier. The thermal barrier has two important functions - it keeps the heat inside during the winter and the cool air inside during the summer.


There are several key elements to creating an effective thermal barrier, one of these is thermal bridging. In wood-frame construction, insulation within stud cavities can lead to thermal bridging issues, which is where weak points in the building envelope allow heat to pass through more easily. Wrapping the home in continuous insulation is a great solution to mitigate thermal bridges, it works like placing a tea cozy over your house to keep the heat where it should be!

Another important aspect of the thermal barrier is the type of insulation used. Insulation materials come in various forms, such as rigid foam, batt insulation, foam, rock wool, wood fiber, and more. The materials range from oil-based foam products to plant-based straw bales with many options in between.

When selecting insulation you need to consider the R-value of the material you want to use. The R-value of a material indicates it's thermal performance, with higher values indicating better performance. In addition to choosing the right thermal performance, it's essential to consider environmental and health factors when selecting insulation to ensure that you choose the best option for your needs.


Embodied Carbon


Insulation plays a crucial role in reducing energy consumption in our homes, but it's important to be mindful of the environmental impact of insulation materials. This is where embodied carbon comes in. Embodied carbon, or upfront carbon, refers to the amount of greenhouse gases emitted during the extraction, manufacturing, and transportation of a product.

Foam insulation has a high level of embodied carbon and the emissions produced during manufacturing and transportation exceed the energy savings that the insulation can provide. Additionally, foam insulation can be hazardous to installers and those who live in the home due to the chemicals used in production.

When it comes to embodied carbon and net zero home retrofits, it's important to consider the amount of embodied, or upfront, carbon in the materials you choose. Take a look at the table below to see the comparison of various insulation materials and their embodied carbon.


A table that shows the comparison of insulation types and their embodied carbon levels

Managing Moisture: The Vapor Barrier


A home's building envelope isn't complete without an effective vapour barrier. When it comes to building a well-insulated and energy-efficient home, the vapor barrier, also known as a vapor retarder, plays a pivotal role in maintaining comfort and durability. It prevents the movement of water vapor between different parts of the structure, reducing the spread of moisture-laden air. It helps to maintain comfort and durability by guarding against issues like mold growth, rot and reduced insulation efficiency within the wall or ceiling cavities.


A young child holding an umbrella in the rain


To ensure effective moisture control, it is essential to choose the right type of vapour barrier based on specific building needs and local climates. Here are some common types:


Polyethylene Plastic Sheeting: Is an affordable and effective option that is available in rolls for wall and ceiling assembly. Proper installation can also turn it into an air barrier, but it may trap moisture in the wall, is prone to punctures, and is challenging to make continuous.


Membrane-Type Barriers: These specialized membranes made from materials like polyethylene, polypropylene, or bituminous materials are highly effective at preventing moisture penetration. They can also be vapor variable, allowing any moisture that may have gotten into a wall or roof to dry out in the right conditions.


Spray foam has been considered as a vapor barrier, but its potential for shrinkage over time limits its effectiveness. Plus, installation and of spray foam it raises both health and environmental concerns. Therefore, we alwys advise to consult with a professional to determine the best type of vapor barrier for your home's needs.



The Building Envelope: Control Layer Location



A cross section showing the assembly of a cold climate wall

When designing a Net Zero home, it is crucial to understand the four control layers of a building envelope to ensure that the house is well-insulated, energy-efficient, and comfortable. These layers work together to control water, air, heat, and moisture, maintaining the home's long-term durability and performance.


In a wall, these layers are arranged from the inside out in the following order: interior finish, structure, and exterior finish.


Each control layer has a specific location in the wall. For instance, the weather barrier is typically located outside the structure, while the air barrier can be anywhere between the interior and exterior finish. The majority of the insulation should be between the vapor barrier and the exterior finish. Finally, the vapor barrier should be on the conditioned side of the wall.


Understanding the location of these control layers is essential to create a well-insulated, energy-efficient, and comfortable Net Zero home.


A bright and comfortable home

Understanding and Managing Your Home’s Control Layers for A Net Zero Retrofit


When planning to renovate your home, it's important to pay attention to the control layers in the building envelope. These control layers can have a significant impact on your home's energy efficiency, indoor air quality, and overall comfort.


Each control layer in the building envelope plays a crucial role in the overall efficiency and sustainability of your home. To achieve a Net Zero home, it's essential to have a good understanding of these concepts and even better to work with a professional who does too. By incorporating these control layers into the design of your home, you can create a comfortable and energy-efficient space that will be a joy to live in for years to come.

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