What is air sealing?

Air sealing is the act of using a material to stop air from passing between two spaces. 

When we look at homes, we want to create a continuous thermal envelope. What this means is that we want to separate conditioned spaces from unconditioned spaces. Your attic that has insulation in it (or should have insulation) is what we call an unconditioned space. Here, you are not living in the attic. You are not heating it, nor are you cooling it. Therefore we want this to be separated as best as possible from the living space. Do you want hot air from the attic to come into your bedroom in the summer while you're trying to live in air conditioning? No! To prevent that, you need a continuous thermal envelope.

Now that thermal envelope we were talking about. If you are upstairs in your home, in a living space, and you look up, you should see a drywall ceiling. Drywall is a material that air seals. The drywall prevents air from passing between your nice, conditioned home and the unconditioned attic. Below is an example of a drywall ceiling with an attic hatch. 

What we are looking at is part of the thermal boundary. The attic hatch leads to the attic. We want to keep the two spaces separated. But what happened? The builders created an access to the attic and did not seal it off properly. They cut a hole in your drywall barrier. As soon as holes go in your drywall barrier, air can now pass between those spaces. Look at the the thermal image, air is passing between those two spaces. The solution is to air seal the attic hatch to prevent air from passing between the two spaces. 

Below is another example of what happens when you have a break in your thermal boundary. The drywall ceiling remains all one temperature, indicated as yellow in the picture below, but by installing a vent there are now air changes occurring between the two spaces. 

Air sealing can be performed in a variety of spaces in the home. They include attic spaces, knee walls, crawl spaces, basements, garage attics, exterior doors, recessed lights, and others. 

By blocking air from moving between a conditioned space and unconditioned space, the home will be more comfortable and efficient. 

The problem is that you want to make sure the air sealing work is performed properly, targeted in the areas that need it, and that you do not seal up the home too much. 

Stay tuned for the next blog post where we discuss the dangers of air sealing.

What is a knee wall?

A knee wall is probably the LEAST COMFORTABLE and most ENERGY INEFFICIENT part of your home. 

A knee wall is an area you've seen hundreds of times and may have no idea what it is till now. 

A knee wall is also an area that do-it-yourselfers normally 'fix' wrongly. 

Physically, a knee wall is an area of a home that would normally be a full attic space. Instead of a full attic, a room is built in that space. The room is typically conditioned (heated and/or cooled) and is drywalled off. 

Now what does a knee wall look like? A few key indicators that you have a knee wall:

• Low sloping ceiling with attic or roof space above that leads down to a wall. The blue wall in the picture below is the knee wall. 
• An attic access that is perpendicular to the floor

From the inside of the attic, a knee wall looks like the image to the left. The wall on the left with yellow insulation is the same wall as the blue wall in the image above. As you can see in the image below, the joists run perpendicular to the wall, which means the joists run below the floor of the living space. As insulation does not stop air flow, cold air in the winter can pass under your floor as well as hot air in the summer. As a side note to this image, the insulation on the knee wall floor was installed upside down. About half of the Do-It-Yourselfers install insulation incorrectly.

From the outside, what does a knee look like? Below is a picture of the same house. The orange represents the walls that form the conditioned space in the bedroom. This is the livable space shown in the first image of this blog post. 

Then you can see the ventilation where air enters into the knee wall space. Unwanted air will travel under the floor, causing discomfort and a severe lack of energy efficiency. 

Now, what are the solutions?

We want to air seal any penetrations or top plates, as we do in all attic spaces. But then for the knee wall, it's important to air seal the wall with Tyvek or foamboard. This will help reduce the wind damage on the insulation to keep it in good shape as well as increase its effectiveness. Then, we bay block the cavities to create a continuous thermal boundary, and block air from passing under the floor. 

Knee walls are tight, complicated areas. Our recommendation is to get an energy audit to first determine your home's air leakage. The recommended solutions all stop air from entering or leaving the house. Not knowing your Building Airflow Standard nor your blower door number can be severely dangerous as you air seal. Air seal too much, and you can create moisture and health problems - bad for both the inhabitants and the home. 

Our recommendation is to get an Energy Audit and have those knee walls air sealed and insulated properly.