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 construction techniques used, your home may have all, some, or no types of control layers. There are four main control layers we’ll discuss today: the water control layer, thermal control layer, vapor control layer, and air control layer.
Control Layers
The primary purpose of a control layer is to manage the movement or flow of heat, moisture, vapor, or air throughout your home. If you’ve been following along in our series, you may already recognize how some of our previous topics, such as Building Code Requirements for Insulation or How can Insulation Prevent Heat Loss?, relate to control layers. Control layers are commonly installed above grade or below grade in your home.
Some common materials used in control layers are:
- Foundation waterproofing
- Air barrier membranes
- Plastic sheeting
- Rigid insulation
- Drywall
- Framing
The Water Control Layer
This control layer, often referred to as the weather barrier, 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 mitigate the infiltration of moisture into your basement from exterior walls and flooring.
Both above and below grade, moisture tries to enter your home through mechanisms such as gravity, pressure differences, diffusion, and capillary action. The water control layer is designed to prevent moisture from entering and to facilitate drying when it does get wet.
Above grade water control needs to:
- Be installed on the exterior side
- Shed rain and snow
- Be durable against wind and weather
Below grade water control needs to:
- Be installed on the interior side
- Be resistant to moisture
- Allow for air flow
What About Waterproofing?
Waterproofing involves coating an exterior foundation wall with an emulsion made of plastic, bitumen, or cement to prevent moisture in the soil from penetrating the basement walls. It provides an additional layer of protection to your foundation wall.
The Thermal Control Layer
This control layer helps prevent temperature movement and heat flow through your home. Insulation plays a significant role in the thermal control layer. The purpose of this layer is to retain heat during colder months and keep it out during the summer.
Heat loss can occur through various areas in your home, including walls, floors, and ceilings. Additionally, windows, doors, and areas where heated and unheated spaces meet, such as around an attached garage, require thermal control layers to reduce heat transfer.
Thermal control layers need to:
- Be resistant to heat flow
- Be installed within cavities or onto exterior or interior surfaces
For a more in-depth look at the types of materials recommended for thermal control layers, check out our blog “Which Type of Insulation is Best For Your Home?” to learn more.
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 Vapor Control Layer
This essential control layer prevents and reduces moisture permeation through your building envelope, keeping different components of your home dry and preventing damage caused by moisture.
Vapor control layers need to:
- Be installed on the interior, or warm, side of insulation
- Cover as much surface area as possible
- Be impermeable to vapor diffusion
- Allow for air flow
Common materials used in vapor control layers include polyethylene, aluminum foil, vapor retardant paints, some insulation materials, and metal or glass. Proper placement of these materials is crucial for their effectiveness.
Vapor 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 air control layer acts as a barrier that prevents interior air from escaping through your building envelope and exterior air from entering. This layer is critical because air is one of the primary ways that heat and moisture travel.
The air control layer works by stopping air from entering or exiting your home, giving you greater control over your indoor environment and reducing strain on your furnace or air conditioning.
Air control layers need to:
- Be completely impermeable to air flow
- Be continuous without breaks, open seams, gaps, or holes
- Be strong enough to withstand differences in air pressure
Materials commonly used in air control layers include polyethylene, house wraps, wood, concrete, drywall, and rigid foam boards. Each of these materials requires specialized tapes, sealants, gaskets, or caulking to ensure their impermeability. Air control layers can be installed on either the interior or exterior of the entire building envelope.
Air Barrier Vs. Vapor Barrier
You may be thinking that air and vapor control layers are very similar – what are the primary differences? An air barrier can be installed anywhere in the building envelope, while a vapor barrier should be installed on the warm side of the insulation. Additionally, a vapor barrier should cover as much surface area as possible but doesn’t need 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 better understand where they need to be installed for optimum performance. In our next installment, we’ll discuss the basic approach to layering air, moisture, and thermal control barriers to create a more efficient building – so stay tuned!
Control layers are crucial for your home’s efficiency and longevity, so understanding these different components is the first step in addressing any problems or planning renovations. At EcoStar Insulation, we’re here to help you navigate the complexities of building science and ensure your home is functioning as it should. If you have any questions about control layers and what your home may be lacking, give us a call at 646-809-1007 or 917-900-1155.
