Attic Air Sealing

A good deal of heat loss in homes is through air leakage. Sealing Air Leaks is often more cost effective than adding wall insulation. 

Prevent Stack Effect

Prevent Wind Effect

Reduce Mechanical Combustion Exhaust Backdraft

What is air sealing, and why does my attic need it more than insulation? Air leakage is sometimes called infiltration, which is the unintentional or accidental  introduction of outside air into a building, typically through cracks in the building envelope  and through use of doors for passage. Source BECP Building Energy Code Program. A leaking conditioned space is drafty. A leaking conditioned space creates unintentional heat escape in winter to the outside and creates the potential for mold growth. When retrofitting existing homes, an air sealed attic floor is the first step to a clean healthy interior. Only then can we focus on active ventilation and additional insulation. 

Weatherization or weatherproofing,  air sealing,  fire-stopping; the goal is clear. Improvements make a house or building resistant to cold weather by adding insulation, weather strips, sealants, or gaskets to seams such as windows, doors, and gaps of dis-similar materials. 

Why Attic Air Seal?  By Definition : Insulation slows the rate of heat transfer in or out of the house. Typically framing cavities ( space between studs ) are insulated with fiberglass, chemical foam, cellulose or mineral wool insulation to trap air. Air is a very good insulator. Picture the air gap between beverage thermos materials; one layer is to hold the beverage, with an air gap between the outer layer does not have contact with the inner layer creating an incredible resistance to heat escape or heat intrusion. 

 Loose fill / batt insulation is designed to trap air between layers but it is not a pressure barrier. A good insulation material will trap air, and keep the air still ( such as closed cell spray foam or rigid foam board.)  

Attic Air Seal highlights and benefits to existing homes. 

1. reduce drafts at the lower levels of the home by stopping heat escape in the winter to the attic

2. reduce heating and cooling bills by eliminating leaks and unintentional air escape from the conditioned space

3. stop the dust ( dead skin and hair ) from clogging the trim covering the gap between the drywall and floor 

4. prevent a mold food source ( condensation / evaporation cycle) 

5. prevent unintentional air exchanges in the conditioned space

On sidewalls of the home, there may be gaps between framing members. 

Green Attic Insulation
A proper air seal of the bypass shown using one part spray foam to air seal the attic floor.

Why is my Home Drafty Downstairs in Winter? 

Heat escapes from the conditioned living space pressure barrier.

Existing Insulation Evidence :  find a perfect black line corresponding with the seam between the drywall and framing called the bypass. This seam is accompanying the gap between the trim / baseboard / drywall / floor of the living space below. This is a direct result of skin dust and hair which is pulled up through stack effect to the attic from temperature differences between the attic and the living space.  The black lines of the photo are not mold ( commonly confused and misdiagnosed) it is skin dust and hair from the living space. The fiberglass insulation does not stop air movement. No loose fill insulation stops air movement. 

To verify this process of finding skin dust and hair in the attic, shake out your blanket in the morning with a bright light and notice the dust that fills the air. This dust is pulled between gaps in the room up and out to the attic. This is the same air that leaks and escapes from the heated bedroom resulting in unintentional air exchanges, a drafty lower level, higher bills, mold food in the form of condensation, premature snow melt, icicles, ice dams and more. 

Air Sealing Attic Floor
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BEFORE air sealing, the discovery of perfect black lines corresponding with seams of the floor and wall from the living space below.

we flip over the existing fiberglass

The Seam Between The Trim / Wall and Floor

Air sealing the attic floor is the solution to the problem. Air sealing the attic floor prevents air movement upward to the attic by pressurizing the living space. Air sealing is a simple concept, but performing attic air sealing requires working in difficult / uncomfortable body positions under temperature stress with itchy old fiberglass in contact with unprotected skin. 

Create an air tight pressure barrier for the conditioned living space.

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Lights fixtures, electrical outlets, plumbing, ductwork vents,  chimneys all create (swiss-cheese) holes in your bedroom ceiling…These are unintentional breaks in your pressure ( air) barrier.

Any unintentional gap /hole in your ceiling creates air movement, air exchanges, is unintentional thermal transfer. Meaning your home is loosing heat in winter, and gaining heat in summer.

  • Seal the Gaps. Mind the Gaps.
  • Sealing the exterior building envelope properly which requires re-caulking every few years in the Chicago area due to extreme heat and extreme cold
  • Air seal the entire attic floor at all seams and penetrations
  • You will see an immediate  considerable improvement in comfort and efficiency.
  • Lower your Air Exchanges per Hour.
  • Lower your unintentional leakage. We spray foam around most of these, including around light fixtures, bathroom fans, open wall cavities, and plumbing stacks.
  • Other items like chimneys and recessed lights require special materials.
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can lights leaking
Can Lights leak Heat into home in the summer and are a major source of heat escape in the winter.

A complete pressure barrier (winter cap)  of the homes top floor is essential to preventing heat escape. 

The can lights puncture the drywall and create ( open windows ) for heat to push its way through and reach the attic vents and go straight to the exterior.  

The can lights box trim  have little holes where heat passes through. 

This causes you to literally heat the outside in winter with your paid gas from your furnace. 

  1. This wasted heat ( wasted energy) raises the cost of heating, but that is often the smallest concern. 
  2. Bigger concerns are the moisture and humidity created in the attic leading to mold
  3. Creates a drafty home by allowing heat escape at the top of the home and air intake at the bottom of the home.  Stack effect will create a cold downstairs with cold air intake around seams regardless of wind or not. 

Air Sealing Can Lights can be performed with a few different sealants, drywall, rockwool, mineral wool covers and or course retrofitting existing bulbs with  Recessed Lighting Trims that stop air leaks. 

DIY Can light covers are challenging in two ways, one is maintaining a true tight seal around the light so it no longer leaks, and the other is accessibility of the can lights. 

Green Attic uses drywall to created air tight fireproof boxes around existing can lights to stop air leaks from the conditioned living space. Air sealing the attic floor is the first step in fixing problems around the home created by stack effect from leaking pressure barrier of the conditioned space. 

Older can lights require a minimum distance around the light housing to prevent a fire. Lights should be replaced with cooler burning bulbs ( older bulbs run around 200-250 degrees Fahrenheit, while new bulbs run much cooler around 100-125 degress Fahrenheit. 

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Can light covers made from drywall and seams sealed with one part fire stop spray foam.
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Can light covers are placed over each can light using drywall and one part spray foam around the seams to create a perfect air seal and prevent heat escape in winter to the attic and outside.

Can light covers are placed over each can light using drywall and one part spray foam around the seams to create a perfect air seal and prevent heat escape in winter to the attic and outside. 

Each can light must be properly sealed to prevent heat escape ( heat rising from the conditioned space). 

The combination of sealed plumbing, hvac, chimney, bypass, and electrical penetrations with sealed can lights creates a properly sealed attic floor. Now we can focus on fresh air balanced intake and exhaust ( ventilation.) 

Can light covers are placed over each existing can light on the top floor of the home which is in direct contact with the attic using drywall and one part spray foam around the seams to create a perfect air seal and prevent heat escape in winter to the attic and outside.

Do I need to air seal my basement?

Yes. There are dissimilar materials that may cause unintentional leakage in the basement, and since it is accessible in most homes, it is a priority for us secondary to attic air sealing. Any work you have done inside your home could be less efficient if your basement is not properly sealed. Air sealing is supplemental to insulation. A free energy assessment where we use our thermal cameras to track heat movement will clear up any questions.

What about the exterior walls?

While wall insulation may be effective, it is installed between stud cavities, so that does not prevent air movement, air infiltration, and unintentional air leakage around the seams of the framing such as the top plates and bottom plates. Air Sealing is done on framing in new construction with energy efficient standards. in existing homes, there are methods to improve the building envelope to prevent drafty homes. Call us for a longer conversation specific to your home.

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Air sealing is one of the most critical features of an energy-efficient home. To add insulation without air sealing first is dereliction of duty. 

To prevent air leakage, it is best to seal the building envelope during construction prior to the installation of the drywall.

A “blower door” test is a good way to identify air leakage paths so that they can be sealed using an appropriate material.

This is the bypass of the hallway and bedrooms. These gaps allow paid conditioned air escape creating a list of preventable problems.

Preventable problems include

  • condensation
  • drafty rooms 
  • mold growth as result of condensation
  • constantly cycling furnace and air conditioner
  • higher than usual energy bills 
  • dusty rooms 
  • reduced air quality 
air seal bypass gap between drywall and framing on attic floor air seal spray foam insulation
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Air Sealing leaks around penetrations in the home is the first and most cost effective step to reducing drafty homes. 

Draftiness can be measured in air exchanges in the conditioned space. 

Keeping the house snug and tight is commonly referred to as weatherproofing your home. This includes blocking drafts around windows, doors, and plugging cracks and gaps created by pipes, hoses, and exhausts. 

Once the home is protected from drafty wind pressure from the exterior, you can begin to focus on air quality and air exchange improvements from the interior. 

Shielding the home from wind pressure is essential to reducing “cold walls” in winter, air exchanges of heated ( paid for conditioned air.) Even if insulation is between studs, draftiness can still occur from wind pressure forcing cold outside air into the walls of through exterior seams. Once the air is in the walls, it move by path of least resistance to the first available opening such as an outlet or seam where the floor and walls meet. 

It is essential to start by sealing the gaps around the outside of the home, this will return your time and material investment many times over. 


A costly error is referred to in the real estate industry as ” topping off insulation.” When the home inspector finds mold typically the process. is to treat the mold and not the CAUSE of the mold. 

We often find mold growing on the sheathing of well insulated attics, because loose fill fiberglass does not stop air movement or heat escape from the living space. Without air sealing the attic floor, the heat will still rise and meet cold winter air from passive ventilation leaving food for mold growth in the form of warm air turning to condensation. The solution is air seal attic floor, baffles and vapor barrier around attic parameter, proper ventilation, and adequate insulation. 

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It if vital to include attic air sealing in any attic insulation project to prevent heat loss, mold, condensation and draftiness in the home. 

conduit electrical penetrations create air pathways for heat escape
Meticulous air sealing is a hard work due to attic temperatures, existing itchy fiberglass, nails on the sheathing and a significant drop to floors below.

Air Sealing the attic floor with one part spray foam is the first step to a comfortable energy efficient home where draftiness is eliminated by stopping heat escape from the heated living in winter.


THIS OLD HOUSE – Pressurized Coagulation Method New Construction 

Air sealing do it yourself video links .

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  1. Wind Effect
  2. Stack Effect
  3. Combustion and Ventilation 

Three types of air exchanges occur within your homes ( conditioned ) space.  The first two are the secret to a comfortable home. The this is the secret to a healthy home. 

Why Do You Need To Air Seal?

Condensation can lead to mold and mildew problems. In hot, humid climates, moisture can enter into wall cavities through exterior cracks and result in costly damage to framing and insulation. In cold climates, gaps in the interior walls allow moisture from warm indoor air to enter wall cavities and attics. This moisture can condense on cold surfaces and lead to structural damage. 
By significantly reducing air leakage, you can reduce or eliminate these problems

A tighter building envelope reduces the amount of unconditioned air, drafts, noise, and moisture that enter your home. Proper air sealing will also minimize temperature differences between rooms. As a result, tight envelopes can maintain a more consistent level of comfort throughout a house. 

This is the main reason to air seal your home. A house works a lot like a smoke stack. Hot air rises through the house until it exits in the attic. If you seal off a   smoke  stack  at the top, the bottom, or both, you don’t have a smoke  stack. In air-sealing a house we are trying to stop the stack effect as much as we can.

An unzipped winter coat doesn’t work very well because it allows air around your body, which makes you cold. An insulated house can also perform poorly if air can get in. There is not a consensus, but nearly half of the energy leakage in a house can be caused by air leakage – that costs a lot of money!

Air leakage accounts for 25 percent to 40 percent of the energy used for heating and cooling and also reduces the effectiveness of other energy efficiency measures such as increased insulation and high-performance windows. By investing a little more money into the improvement of your home, you will effectively be putting more money back into your pocket for years to come.

Do it yourself (DIY) air sealing / weatherization tips for your home.

Keeping the house snug and tight making it more comfortable includes attic air sealing and exterior weather sealing. A few dollars spent and an afternoon of sealing will pay dividends for years. 

  1. Keep your window seams clean. When the windows collect dirt it combines with condensation and hardens making it impossible to get a clean tight seal, the weatherstrip functionality is compromised and air can leak in from “wind pressure” 
  2. Ensure weatherstripping around doors is correct and the door is not loose when pushed with pressure from your hand  it should remain unmovable. If the door can move then there is an unintentional gap and air infiltration. Adjust the strike plate / latch to ensure the door is closed snug compressing the intended weather strip.  
  3. Seal the seam between the foundation and siding to prevent air infiltration to the interior walls which comes out the path of least resistance such as baseboard and electrical outlets. 
Green Insulation Experts

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Comfortable Doesn't Have to be Costly

Attic insulation can reduce heating bills by up to 50%. Get a free estimate from our team of insulation experts.

  • No more drafty rooms
  • Better air quality
  • Pay less on your heating & cooling bills
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