Air Sealing and Insulation PDF Print E-mail

Sealing and Insulation

We need to use a whole-house systems approach

Before developing an air sealing strategy, you should also consider the interaction between any air sealing materials and techniques with other building components, including the following, Insulation, Moisture control, Ventilation. insulation, moisture control andvVentilation.

Note that air sealing alone can't replace the need for proper insulation throughout your home, which is needed to reduce heat flow.



The exterior of your home is called the "envelope" or shell. The insulation, outer walls, ceiling, doors, windows, and floors all work together to control airflow in and out of the structure, repel moisture, and prevent heat from being lost or gained inside your home.

Always air seal before adding insulation, then seal up holes, weather strip doors, caulk pipes and wires, insulate attic floors, basements, and crawl space walls. Any air sealing efforts will complement your insulation efforts, and vice versa. Proper moisture control and ventilation strategies will improve the effectiveness of air sealing and insulation, and vice versa. Moldy and dusty air can enter a leaky house through such areas as attics or foundations. This air in the house could cause health problems.

The recommended strategy in both new and old homes is to reduce air leakage as much as possible and to provide controlled ventilation as needed.

Air leakage, or infiltration, occurs when outside air enters a house uncontrollably through cracks and openings. Properly air sealing such cracks and openings in your home can significantly reduce heating and cooling costs, improve building durability, and create a healthier indoor environment.

First, make a list of obvious air leaks (drafts). The potential energy savings from reducing drafts in a home may range from 5 to 30% per year, and the home is generally much more comfortable afterward.

Check for indoor air leaks, such as gaps along the baseboard or edge of the flooring and at junctures of the walls and ceiling. Check to see if air can flow through these places:

  • Electrical outlets
  • Switch plates
  • Window frames
  • Baseboards
  • Weather stripping around doors
  • Fireplace dampers
  • Attic hatches
  • Wall- or window-mounted air conditioners.

Also look for gaps around pipes and wires, electrical outlets, foundation seals, and mail slots. Check to see if the caulking and weather stripping are applied properly, leaving no gaps or cracks, and are in good condition.

Inspect windows and doors for air leaks. See if you can rattle them, since movement means possible air leaks. If you can see daylight around a door or window frame, then the door or window leaks. You can usually seal these leaks by caulking or weather stripping them. Check the storm windows to see if they fit and are not broken. You may also wish to consider replacing your old windows and doors with newer, high-performance ones. If new factory-made doors or windows are too costly, you can install low-cost plastic sheets over the windows.

If you are having difficulty locating leaks, you may want to conduct a basic building pressurization test:

  1. First, close all exterior doors, windows, and fireplace flues.
  2. Turn off all combustion appliances such as gas burning furnaces and water heaters.
  3. Then turn on all exhaust fans (generally located in the kitchen and bathrooms) or use a large window fan to suck the air out of the rooms.

This test increases infiltration through cracks and leaks, making them easier to detect. You can use incense sticks or your damp hand to locate these leaks. If you use incense sticks, moving air will cause the smoke to waver, and if you use your damp hand, any drafts will feel cool to your hand.

On the outside of your house, inspect all areas where two different building materials meet, including:

  • All exterior corners
  • Where siding and chimneys meet
  • Areas where the foundation and the bottom of exterior brick or siding meet.

You should plug and caulk holes or penetrations for faucets, pipes, electric outlets, and wiring. Look for cracks and holes in the mortar, foundation, and siding, and seal them with the appropriate material. Check the exterior caulking around doors and windows, and see whether exterior storm doors and primary doors seal tightly.

When sealing any home, you must always be aware of the danger of indoor air pollution and combustion appliance "backdrafts." Backdrafting is when the various combustion appliances and exhaust fans in the home compete for air. An exhaust fan may pull the combustion gases back into the living space. This can obviously create a very dangerous and unhealthy situation in the home.

In homes where a fuel is burned (i.e., natural gas, fuel oil, propane, or wood) for heating, be certain the appliance has an adequate air supply. Generally, one square inch of vent opening is required for each 1,000 Btu of appliance input heat. When in doubt, contact your local utility company, energy professional, or ventilation contractor.

Detecting Air Leaks

You may already know where some air leakage occurs in your home, such as an under-the-door draft, but you'll need to find the less obvious gaps to properly air seal your home.

For a thorough and accurate measurement of air leakage in your home, hire a qualified technician to conduct an energy audit, particularly a blower door test. A blower door test, which depressurizes a home, can reveal the location of many leaks. A complete energy audit will also help determine areas in your home that need more insulation.

Without a blower door test, there are ways to find some air leaks yourself. First, look at areas where different materials meet, such as between brick and wood siding, between foundation and walls, and between the chimney and siding. Also inspect around the following areas for any cracks and gaps that could cause air leaks:

  • Door and window frames
  • Mail chutes
  • Electrical and gas service entrances
  • Cable TV and phone lines
  • Outdoor water faucets
  • Where dryer vents pass through walls
  • Bricks, siding, stucco, and foundation
  • Air conditioners
  • Vents and fans.

You can also try these steps to depressurize your home to help detect leaks:

  1. Turn off your furnace on a cool, very windy day.
  2. Shut all windows and doors.
  3. Turn on all exhaust fans that blow air outside, such as bathroom fans or stove vents.
  4. Light an incense stick and pass it around the edges of common leak sites. Wherever the smoke is sucked out of or blown into the room, there's a draft.

If you don't want to turn off your furnace, you can just turn on all your exhaust fans to depressurize your home.

Other air-leak detection methods include the following:

Shining flashlight at night over all potential gaps while a partner observes the house from outside. Large cracks will show up as rays of light. Not a good way to detect small cracks.
Shutting a door or window on a piece of paper. If you can pull the paper out without tearing it, you're losing energy.

“Sealing up Your Home’s Leaks” by John Krigger from Home Energy magazine An article that explains how air circulates in a house and where it might leak.

DOE Energy Efficiency and Renewable Energy (EERE) site also explains how to find leaks.
Air Sealing



A proper balance between all of these elements will also result in a more comfortable, healthier home environment.

Air sealing

Insulation and Air Sealing

Air Sealing an Existing Home

Air Sealing for New Home Construction

Air sealing is an important factor when constructing an energy-efficient home. These are some air sealing techniques and materials:

ENERGY STAR has a Home Sealing site: They also have a 22 page booklet on Sealing air leaks and adding attic insulating at


CAULKING Caulking is easy and one of the most cost-effective energy efficiency improvements you can make. Anywhere different building materials meet or wires enter your home, there are gaps which collectively contribute to a significant loss of heat or cooling. Check for gaps inside and out when you paint or at least every 5 or 6 years. Check your attic and all accessible exterior walls in your basement or unfinished rooms to make sure they are well insulated.

Caulk and weather-strip all leaky windows, baseboards and doors.
Caulk all exterior openings for plumbing, and electrical service and look for other openings that need to be sealed.
Make sure all attic vents and ducts are properly sealed. Sealing your ducts can save money and help you consistently heat every room.
Especially if you can't replace windows with more energy-efficient ones, then caulk and weather strip them.

Caulking -Selecting the Types and applications

Weather stripping - Types and Application

The Rocky Mountain Institute has a Home Resource Efficiency site that includes nine Home Energy Briefs, Number 1 is on the Building Envelope , including information on insulation and sealing air leaks at


Adding new insulation can bring dramatic savings, especially in homes built before 1970.

Simply upgrading the insulation in your attic to R-30 or R-38 can save as much as 25% on cooling and heating costs. Attic: increase attic insulation to R-50 in cold climates, R-38 in milder climates, and R-30 plus a radiant barrier in hot climates.

Heat loss through the ceiling and walls in your home could be very large if the insulation levels are less than the recommended minimum. When your house was built, the builder likely installed the amount of insulation recommended at that time.

If the attic hatch is located above a conditioned space, check to see if it is at least as heavily insulated as the attic, is weather stripped, and closes tightly. In the attic, determine whether openings for items such as pipes, ductwork, and chimneys are sealed. Seal any gaps with an expanding foam caulk or some other permanent sealant.

While you are inspecting the attic, check to see if there is a vapor barrier under the attic insulation. The vapor barrier might be tarpaper, Kraft paper attached to fiberglass batts, or a plastic sheet. If there does not appear to be a vapor barrier, you might consider painting the interior ceilings with vapor barrier paint. This reduces the amount of water vapor that can pass through the ceiling. Large amounts of moisture can reduce the effectiveness of insulation and promote structural damage.

Make sure that the attic vents are not blocked by insulation. You also should seal any electrical boxes in the ceiling with flexible caulk (from the living room side or attic side) and cover the entire attic floor with at least the current recommended amount of insulation.

Checking a wall's insulation level is more difficult. Select an exterior wall and turn off the circuit breaker or unscrew the fuse for any outlets in the wall. Be sure to test the outlets to make certain that they are not "hot." Check the outlet by plugging in a functioning lamp or portable radio. Once you are sure your outlets are not getting any electricity, remove the cover plate from one of the outlets and gently probe into the wall with a thin, long stick or screwdriver. If you encounter a slight resistance, you have some insulation there. You could also make a small hole in a closet, behind a couch, or in some other unobtrusive place to see what, if anything, the wall cavity is filled with. Ideally, the wall cavity should be totally filled with some form of insulation material. Unfortunately, this method cannot tell you if the entire wall is insulated, or if the insulation has settled. Only a thermographic inspection can do this.

If your basement is unheated, determine whether there is insulation under the living area flooring. In most areas of the country, an R-value of 25 is the recommended minimum level of insulation. The insulation at the top of the foundation wall and first floor perimeter should have an R-value of 19 or greater. If the basement is heated, the foundation walls should be insulated to at least R-19. Your water heater, hot water pipes, and furnace ducts should all be insulated. For more information, see our insulation section.

Insulation and Air Sealing at EERE- Energy Efficiency and Renewable Energy-

They also have further information at these sites:

How Insulation Works
Adding Insulation to an Existing House
Selecting Insulation for New Home Construction
Where to Insulate
Types of Insulation

The R-Value of Insulation

An R-value indicates an insulation's resistance to heat flow. The higher the R-value, the greater the insulating effectiveness.

The R-value depends on the type of insulation and includes its material, thickness, and density. When calculating the R-value of a multilayered installation, add the R-values of the individual layers. Installing more insulation in your home increases the R-value and the resistance to heat flow.

The effectiveness of an insulation's resistance to heat flow also depends on how and where the insulation is installed. For example, insulation that is compressed will not provide its full rated R-value. The overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself because some heat flows around the insulation through the studs and joists. Therefore, it's important to properly install your insulation to achieve the maximum R-value.

The amount of insulation or R-value you'll need depends on your climate, type of heating and cooling system, and the section of the house you plan to insulate. For more information, see our information on adding insulation to an existing house or insulating a new house.

Insulation works best when air is not moving through or around it. Therefore, it is very important that air leaks be sealed to ensure that you get the full performance out of any insulation that is installed.

Insulation level are specified by R-Value. R-Value is a measure of insulation's ability to resist heat traveling through it. The higher the R-Value the better the thermal performance of the insulation. The Recommended Levels of Insulation is at This table can help you determine what is most cost-effective for your home. For more comprehensive information, review the Department of Energy's online Insulation Guide.

If you are concerned about how tight your home is, you can hire an energy specialist who can perform leakage tests using diagnostic tools, and make sure all combustion appliances are operating properly If a home is too tight, fresh air ventilation can be added.

To identify your old insulation.

If your house was insulated with vermiculite insulation it could contain asbestos. Take special precautions if your home has vermiculite insulation. Information and photos are at (

Duct Insulation

Properly insulating air ducts located in unconditioned spaces such as attics, crawl spaces, garages, or unfinished basements can help improve your home's energy efficiency.

Air ducts supply conditioned air from your space heating and cooling equipment to your living spaces. They also return an equal volume of air back to the equipment to be conditioned again.

Ducts are typically made out of thin metal materials that easily conduct heat. Therefore, uninsulated or poorly insulated ducts in unconditioned spaces can lose through conduction 10%–30% of the energy used to heat and cool your home. The heating and cooling equipment then has to compensate for the heat loss and gain by conditioning additional air. This added conditioning raises a homeowner's energy bills. In addition, when ducts lose heat through conduction, rooms served by long duct runs can experience "cold blow" during the winter because they usually have lower heating-supply temperatures.

Ducts in conditioned spaces experience minimal conductive losses and gains since they are exposed to indoor air temperatures. However, these ducts may also require some insulation to prevent condensation on duct walls and to ensure that conditioned air is delivered at the desired temperature.

Illustration of a person sealing ducts. The duct is being sealed along the joint with duct sealant. A cutout shows a close-up of the joint with the sealant around it.


HVAC contractors typically insulate ducts using rigid fiber board insulation. They have a table showing the recommended R-values by climate for duct insulation in unconditioned spaces.

Further suggestions
Install a radiant barrier in your attic if you live in the Sunbelt states.
It is also a good idea to add insulation to your floors and walls, but this can be difficult and it is best to consult a contractor.
Insulate Foundation: insulate inside rim joist and down the foundation wall to below frostline to
at least R-19 in cold climates and to R-11 or better in moderate climates. Remember to caulk first.
Insulate the first three feet of hot and inlet cold water pipes.
Seal and insulate warm-air heating (or cooling) ducts.
Make insulating shades for your windows, or add insulating storm windows (or, in a southern climate, shade sunny windows or add solar gain control films).
Basement: insulate the ceiling above crawlspaces or unheated basements to at least R-19 in cold climates. If your basement is heated, insulate the inside of basement walls instead to R-19 or more above grade and to R-11 or more below grade. Basement or foundation insulation is usually not needed in hot climates.
Walls: adding wall insulation is more difficult and expensive, but may be cost-effective if your house is uncomfortable.
Get a comprehensive energy audit, including a blower door test, to identify sources of air infiltration.

Investigate reflective insulation (a radiant barrier)
Reflective insulation (also called a radiant barrier) is a metallic foil material (usually aluminum) designed to block radiant heat transfer across open spaces. According to the Dept. of Energy's (DOE) Radiant Barrier Fact Sheet, reflective insulation can be effective at reducing cooling bills and, possibly, reducing heating bills in homes. DOE also states that the performance and long-term cost-effectiveness of the product depends on number of factors, including: where the product is installed, how the product is installed, and the amount of existing insulation currently in the home. DOE and the Florida Solar Energy Center (FSEC) have excellent and detailed web sites that explain how the product works, general guidance on the best way to install the product, which climates the product is most cost effective, and energy savings one could reasonably expect. Please read through these sites for more information on this product category:




Choosing the Right Ventilation Equipment

A good ventilation system involves getting an energy-efficient, quiet fan; designing and installing the ducts properly; and choosing appropriate accessories and controls for your system.

When creating an energy-efficient, airtight home through air sealing techniques, it's very important to consider ventilation. Unless properly ventilated, an airtight home can seal in indoor air pollutants. Ventilation also helps control moisture—another important consideration for a healthy, energy-efficient home.

Purpose of Ventilation

Your home needs ventilation—the exchange of indoor air with outdoor air—to reduce indoor pollutants, moisture, and odors. Contaminants such as formaldehyde, volatile organic compounds, and radon can accumulate in poorly ventilated homes, causing health problems. Excess moisture in a home can generate high humidity levels. High humidity levels can lead to mold growth and structural damage to your home.

To ensure adequate ventilation, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) says that a home's living area should be ventilated at a rate of 0.35 air changes per hour or 15 cubic feet per person, whichever is greater.

Ventilation Strategies
There are three basic ventilation strategies:

Natural ventilation

Uncontrolled air movement into a home through cracks, small holes, and vents, such as windows and doors. Not recommended for tightly sealed homes.
Whole-house ventilation
Controlled air movement using one or more fans and duct systems.
Spot ventilation
Controlled air movement using localized exhaust fans to quickly remove pollutants and moisture at their source. Typically used in conjunction with one of the other strategies.

See also No Regrets Remodeling at


Properly controlling moisture in your home will improve the effectiveness of your air sealing and insulation efforts, and vice versa. Thus, moisture control contributes to a home's overall energy efficiency.

The best strategy for controlling moisture in your home depends on your climate and how your home is constructed. Before deciding on a moisture control strategy for your home, you may first want to understand how moisture moves through a home.

Moisture control strategies typically include the following areas of a home:

In most U.S. climates, you can use vapor diffusion retarders in these areas of your home to control moisture.

Proper ventilation should also be part of a moisture control strategy.


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