How The Right Control Layers Make an Efficient Home?

This week in our series on building sciences and home anatomy we’re going to be talking about control layers and how they can affect your indoor environment and home’s permeability. Control layers are an important part of your home’s system; depending on the age and what construction techniques were used during building, your home may have all, some, or no types of control layers. There are four main control layers we’re going to talk about today: the water control layer, thermal control layer, vapour control layer, and air control layer.

Control Layers

The main purpose of a control layer is to control the movement or flow of heat, moisture, vapour, or air throughout your home. If you’ve been following along in our series, you may already recognize how some of our previous topics, like Building Code Requirements for Insulation or How can Insulation Prevent Heat Loss? relate to control layers. There are two common areas where control layers are installed in your home - above grade or below grade.

Some common materials used in control layers are:

• Foundation dampproofing
• Moisture barrier
• Polyethylene
• Rigid insulation
• Drywall
• Framing

The Water Control Layer

This control layer is more frequently referred to as the weather barrier - above grade protects the exterior parts of your home’s walls from the effects of wind, water, snow, and other weather conditions. Below grade, the water control layer - helps to mitigate the infiltration of moisture into your basement from exterior walls and flooring.

Above and below grade moisture tries to enter your home through a number of mechanisms, such as gravity, pressure differences, diffusion, and capillary action. The water control layer is designed to prevent the moisture from making its way in, and also to help it dry out when it does get wet.

Above grade water control needs to be:

• Installed towards the exterior
• Able to shed rain and snow
• Be durable against wind and weather

Below grade water control needs to be:

• Installed towards the interior
• Resistant to moisture
• Can allow air flow

What About Dampproofing?

Dampproofing is when an exterior foundation wall is coated with an emulsion made of plastic, bitumen, or cement that helps to prevent moisture in the soil from moving through the basement walls into your home. It can be an excellent way of adding another layer of protection to your foundation wall.

The Thermal Control Layer

This control layer is the one that helps to prevent temperature movement and heat flow through your home - as you might already expect, insulation plays a huge role in the thermal control layer! The purpose of this layer is to keep in heat during the colder months and to keep it out during the summer.

Heat loss occurs in your home through a number of different places: walls, floors, and ceilings are the obvious places, but windows, doors, and areas where unheated and heated spaces meet - like around an attached garage - also require thermal layers to help reduce heat transfer.

Thermal control layers need to be:

• Resistant to heat flow
• Installed within cavities or onto the exterior or interior surfaces

For a more in-depth look at the kind of materials we recommend for thermal control layers, check out our blog Which Type of Insulation is Best For Your Home? to learn more about what we recommend.

Insulating thermal control layers should be installed in the:

• Attic and roof
• Overhangs and exposed flooring
• Headers
• Above and below grade walls
• Slab and foundation

The Vapour Control Layer

This key control layer in your home prevents and reduce moisture from permeating your building envelope, helping to keep the different components of your home dry and preventing damage caused by moisture.

Vapour control layers need to be:

• Installed on the interior, or warm, side of insulation
• Cover as much surface area as possible
• Be impermeable to vapour diffusion
• Can allow air flow

Some common materials used in vapour control layers are polyethylene, aluminum foil, vapour retardant paints, some insulation materials, and metal or glass. Placement of these materials, like anything in home building, is crucial to their efficacy.

Vapour control layers should be placed in:

• The roof or ceiling
• Exterior walls above and below grade
• The slab and foundation

The Air Control Layer

The last control layer we’re going to talk about today is the air control layer, the barrier that helps stop interior air from escaping through your building envelope - or exterior air getting in! This layer is a critical part of your home in part because air is one of the primary ways that both heat and moisture travel.

The air control layer works by stopping air from entering or exiting your home, which allows you greater control over your indoor environment and less wear and tear on your furnace or air conditioning.

Air control layers need to be:

• Absolutely impermeable to air flow
• Continuous, with no breaks, open seams, gaps or holes
• Strong enough to withstand differences in air pressure

Materials that we see commonly used in air control layers are polyethylenes, house wraps, wood, concrete, drywall, and rigid foam boards. Each of these materials requires specialized tapes, sealants, gaskets, or caulking to ensure their impermeability. All air control layers can be installed in either the interior or exterior of the entire building envelope.

Air Barrier Vs. Vapour Barrier

You may be thinking that air and vapour control layers are very similar - what are the primary differences? To start, an air barrier can be installed anywhere in the building envelope, while vapour barriers should be installed to the warm side of the insulation. Additionally, the vapour barrier should cover as much surface as possible, but isn’t required to be continuous in the same way an air control layer must be.

What’s Next?

Now that you’re aware of the different control layers present in your home, you can be better prepared to understand where they need to go to provide optimum performance. Next month we’ll be going into the basic approach for layering your air, moisture, and thermal control barriers to make a more efficient building - so stay tuned!

Control layers are a key part of your home’s efficiency and longevity, so having an understanding of all these different parts is the first step in addressing any problems or renovations. At EcoStar Insulation, we’re here to help untangle the complexities of building science and ensure your home is running as it should be. If you have any questions about control layers and what your home may be missing, give us a call at (647) 799-3106.