From your energy audit, you have identified your home's air leaks. Tackle air sealing around your home first. As you get started, keep the phrase“Build it tight and ventilate right”in mind. As part of the wall system, improve your insulation and make sure your home ventilates properly at this time. When tightening the building envelope, it is critical to test the combustion safety of any natural gas appliances, water heaters and furnaces!

When done correctly, the walls of your home should be designed to dry to the outside. This means that moisture that inevitably enters your wall through diffusion should dry through the exterior face of the wall and not the other way around to prevent mold growth and moisture damage.

Our homes require air exchange provide adequate ventilation and maintain healthy indoor air quality, and to naturally ventilate combustion appliances like gas stoves and hot water heaters as well as to remove moisture and pollutants. There are two ways fresh air enters our homes - infiltration (uncontrolled air leakage of unknown origin which is bad) and ventilation (intentional ventilation of known origin which is preferred.) Air leaks or infiltration allow moisture and pollutants through your walls, as well as resulting in higher energy demands to heat and cool your home.  This can account for anywhere from 5 to 40% of a home's heating costs. Proper air sealing and ventilation controls the movement of air and air vapor, and is typically relies on mechanical ventilation to ensure enough fresh air. Bath and kitchen fans may provide enough fresh air, or you may consider heat or energy recovery ventilators (HRV or ERV) which provide greater energy efficiency.


Air Sealing

Air sealing must be done in conjunction with moisture management and insulation improvements in mind. Air sealing, moisture management, and insulating work together to create a more comfortable indoor environment.

  • Moisture management prevents water vapor in the air from condensing when it goes from warm to cold (destroying insulation) as it passes through air leaks in and out of your wall.
  • Air sealing stops the air movement and condensation.
  • Proper insulation creates a thermal envelope to efficiently manage your heating and mechanical ventilation.

A significant portion of the air leakage in existing homes is through small cracks or spaces around doors and windows or other penetrations through the walls of a home. Because these leaks result in additional heating costs, air sealing is exceptionally cost-effective. Typically, a few tubes of caulk, some weatherstripping, and a couple of Saturday afternoons can make a difference in your home’s comfort and your heating bills.

Ice dams are a common problem to many Midwest homeowners. Ice dams occur when snow melts from heat escaping through the roof because of improper air sealing, and ice builds up on the edge of your roof preventing melted ice from draining off. Learn more, including how to resolve problems.

Sealing Bypasses

A bypass is an area that allows conditioned air to pass into an unconditioned area of your home. Most commonly, this occurs at walls and ceilings adjacent to unheated garages, attics, floor cavities, and porches. Attic bypasses in particular can be difficult to identify as they are often covered with insulation. They can be found where conditioned space meets an unconditioned space such as areas where the exterior wall framing meets the floor of the attic, and where vents, chimneys, can-light housings and other objects penetrate the floor of your attic.

Bypasses can be identified through your home energy audit. Since heat rises, warm air quickly passes through and around these penetrations. This is why it's important make sealing attic bypasses a priority. Insulation alone will not do the trick; you'll need something solid, an air barrier, to stop the air passage through these openings. Your ceiling assembly of drywall or plywood is intended to act as an air barrier and is integral component of sealing bypasses. If your home has a tiled drop-ceiling, the air barrier must be created by something seamless like a plastic air barrier. To seal bypasses, first perform minor air sealing by caulking any cracks and penetrations; use weather stripping and rigid insulation to insulate around the edges of attic hatches. Next, you'll need to flash around heated penetrations such as chimneys and flues to build a safe fire barrier between the chimney/flue and attic insulation.

Recessed can lights are often be a source of air leakage into the attic; this is often visible by discoloration or dust collection on the ceiling around the light.  Consider replacing your fixtures and look for new recessed lighting products that are IC-rated and have been tested to ASTM E-283 standards. This means that the fixture does not exceed established maximum air leakage rates. If you’re not ready to replace your fixtures, construct an airtight box with at least 3” clearance around the entire fixture using fire-rated materials to allow insulation to surround the fixture without creating a fire hazard. Learn more about how to seal other attic conditions and penetrations.  Once air sealing is complete, you can insulate the attic floor.

When creating a new building envelope, the latest building science calls for a vaporbarrier behind drywall and an exterior air barrier on the outside surface of walls behind the siding. These minimize bypasses. Explore adding vapor barriers during a remodel if you are replacing drywall or creating a new interior space and air barriers during exterior siding renovations. Insulate and seal around outlets, windows, and any other penetrations.  In existing homes, bypasses at walls, floors, and roof attachments are handled similarly to attic bypasses.  Depending on the type of insulation you have, the vapor barrier is often a layer of plastic that can be attached to your studs, covering insulation.  Some rigid insulation products have air sealing properties built in.  Seal and insulate vertical surfaces as you would an attic to improve your home’s efficiency. 

Be aware that most newer basements have a vapor barrier underneath the slab to prevent ground moisture from penetrating the foundation.  Basement walls should have neither an exterior nor interior vapor barrier. Many new foundation walls have an exterior-applied dampproofing to resist groundwater penetration. Unlike the rest of the building envelope, basement walls should promote inward drying.  Learn more about basement wall assemblies from the Building Science Digest document.


Once you've determined your construction project, you'll need to find the right type of insulation product for the task at hand. 

Proper installation is critical to insulation performing properly. It's best to work with a building scientist or home performance contractor to determine the type of insulation, R-value to achieve, and how to install it with proper air sealing. A building scientist can also help improve durability by confirming the insulation is installed properly with a blower door test and infrared scan.

If your project is:

New construction of an addition, with unfinished or open wall cavities / floor / ceiling, use:
Bio-based spray foam, Natural fiber batt, Natural fiber loose fill, Expanded Polystyrene (EPS) Rigid Board insulation

Insulating existing enclosed wall cavities, use:

Bio-Based spray foam, Natural Fiber Loose Fill

Attic insulation, use:

Bio-based spray foam, Natural fiber batt, Natural fiber loose fill

Interior foundation (basement) insulation, use:

EPS Rigid Board insulation

Learn more about what types of insulation to use where through the Energy Savers - Types of Insulation.

Petroleum-based rigid board insulation that uses HCFCs.

Products that are non-recyclable or made from raw materials.

Insulation types vary greatly in cost. Certain types of insulation require higher installation costs but may yield a better lifetime performance or higher R-value, providing a better payback via energy savings. Using more of a lower-cost insulation to increase R-value is a feasible option but may require increasing wall thickness, which can add construction costs.

Environmental Impacts

Whenever possible, look for products with recycled or bio-based content and compare the lifetime performance and environmental impact of different products. Learn more

Choosing Insulation

Choosing Insulation for a Project Not all insulation products work equally well in all scenarios. 
For some recommendations on which products tend to fit which uses. 

Learn more


With any home improvement project, research reputable installers before hiring a contractor. Learn more

Additional Resources:

Drainage Planes, Flashing, vapor barriers, & moisture management

Drainage Planes

Establishing a proper drainage plane on the exterior of your home will help avoid mold and moisture. This prolongs the life of building materials substantially and contributes to a healthier indoor environment. Moisture inevitably gets behind your siding or exterior finish. Drainage planes are created by lapping the surfaces of exterior building materials so that water drains down and away from the interior of the wall. Typically, they are made using a combination of house-wrap, building felt, or paper and flashing around widows, doors, and other openings. In our climate, all building wraps should be vapor permeable in order to promote outward drying of any moisture that may enter the wall cavity. Building wraps help reduce warm air from leaking out of your home during heating seasons, and they also reduce hot outside air from entering your home in summer months. This can help reduce cooling needs in the summer and contributes to an overall more air-tight home.

Additional Resources:


Windows, doors, vents, or any other type of opening or wall penetration are opportunities for moisture and air to get in or out of your home. This does not mean that we should build our homes to be dark, windowless boxes. The solution is to properly flash around all openings so air flow and moisture can't get in to walls and do damage. Flashing is an integral part to maintaining an effective drainage plane. It must be installed so that layers of material overlap to send water away from the interior of the wall and let it run off the outside harmlessly. Flashing around window heads, jambs, and sills should be done with self-adhering elastomeric products, metal, or plastic flashing components. Avoid glues & tapes as these products tend to fail over time. Talk to your installer about what type of flashing products they use.

Vapor Barriers/ Vapor Diffusion Retarders (VDR)

A vapor barrier, or more accurately, a vapor diffusion retarder (VDR), is material that slows the rate of which water can move through a material. By diffusion and air movement, water vapor can move through walls and roofs. This is why it is important to have both an air barrier (ie. housewrap) on the exterior of your home, and a VDR on the interior of your home. This promotes outward drying of any moisture that may enter your wall cavities. VDRs should be installed on the interior of a wall, behind drywall or another finish surface. If you're replacing wall paneling or drywall during your remodel, now is the time to install a VDR! Some materials, like polyethelene sheeting, act as both an air barrier and VDR. Other products, like paper-faced batt insulation, or even paints and wall coatings offer built-in VDR capabilities. While these membranes are typically thinner than a sheet applied product, the most important thing to having an effective VDR is continuity. A seamless membrane on the warm side of the wall will offer better VDR performance.

Learn more about installing vapor diffusion retarders.