Seal the Deal: Boost Energy Efficiency with a Sealed and Insulated Attic and Basement
90% of homes in the United States are under-insulated, according to ENERGY STAR, the federal government's program for energy efficiency.
Our one step this week is Insulating 101: Sealing and Insulating Attics and Basements. Of all the areas in a building, sealing and insulating the basement and attic does the most good due to the “chimney effect.” Because gravity pulls down denser cold air, displacing warm air, the further a hole is below the neutral plane of a building, the faster cold air moves through it, and the higher a hole is above the neutral plane, the faster warm air moves through it. Sealing holes at the bottom and top of air columns keeps air from leaking in and out. Once holes are sealed to keep air in place, insulation can reduce the rate of heat gain or loss through walls and ceilings.
The One That Matters Most
To know how well you have sealed and insulated your attic and basement, this indicator matters most:
How much energy you use per year.
Sustainable Practice: Insulating 101
Sealing and Insulating Attics and Basements
Keep air from flowing through walls and ceilings by sealing holes in basements and attics. Add insulation after preventing airflow.
Equipment and Materials
Caulk
Caulk gun (optional)
Expanding foam (optional)
Foam backer rod (optional)
Smoke stick (optional)
Weatherstripping
Insulation
Steps
Inspect basements and attics for air gaps and insulation levels.
Fill in holes with caulk or foam.
Add insulation after sealing holes.
Install weatherstripping seals around any doors, including attic hatches.
Discussion
For buildings that are heated or cooled, creating an air-tight structure reduces the amount of energy required to maintain comfortable and healthy indoor temperatures and humidity levels. In summer, when air conditioning is in use, cool, dry air tends to leak out of holes near ground level, drawing in humid, warm air through holes near the roof. In winter, when heating is in use, cold, damp air tends to leak in through holes near ground level, forcing dry, warm air out through holes near the roof.
On a hot summer day when air conditioning is running, you can inspect the outside perimeter of your home to look and feel for cool breezes leaking out through gaps in your walls. You may find holes around pipes and conduits, which you can fill with caulk or expanding foam. Another area where air may leak is in casings around windows or doors that were not properly sealed and insulated during construction. For large gaps (bigger than a half inch), you can stuff in a foam backer rod and then caulk or foam around it. You can also use a smoke stick or smoke pencil inside your basement to find areas where cold air is being forced out. Smoke will be drawn to gaps where air is leaving the building.
On a cold winter day, when the heating is running, you can inspect the inside of your basement or the baseboard of your first floor. You can feel cold drafts with the back of your hand. You can use smoke sticks indoors to find places in or near the ceiling where warm air is being forced out of the building.
Remember, the direction of airflow reverses in summer and winter. In summer, if indoors is cooler than outdoors, cold air will leak out of your basement. In winter, if indoors is warmer than outdoors, cold air will leak into your basement.
Energy efficiency professionals can test how airtight a building is by using a fan to create a 50-pascal pressure differential between indoor and outdoor air. By measuring how many cubic feet per minute of air a fan must move to create this pressure differential, a blower door test can determine an air change per hour (ACH) rating. An ACH of 0.6 or below indicates that a building is very airtight.
If your home has an ACH of 4 or more, so much air is blowing through that the energy effect of insulation is relatively minor. If you don’t reduce airflow, adding more insulation won’t make much difference. Once ACH is below 4, then air stays inside for 15 minutes or more on average, long enough that insulation levels can help keep this air cool in the summer and warm in the winter.
Different insulating materials, such as cellulose, mineral wool, and foam boards, have different resistance to thermal energy flow (R-value). The more inches of insulation, the higher the R-value. ENERGY STAR, the United States federal government’s energy efficiency program, recommends that residential structures in warm southern climates have 13″ to 14″ of insulation (R-38) and in cold northern climates have 16″ to 18″ of insulation (R-49) in the attic.
Definitions
Air Changes per Hour (ACH) at 50 pascals: how many times per hour the total air volume is completely replaced when there is a differential pressure of 50 pascals between outside and inside
Conditioned air: indoor air that is heated or cooled
Insulation: material designed to reduce the rate of energy flow
Neutral plane: a horizontal layer of indoor air that has neutral buoyancy, being at the same pressure indoors and outdoors
R-value: thermal resistance per unit area
Troubleshooting
You are having a hard time finding air leaks:
Turn off your furnace and any other fuel-burning appliances.
Close all windows and doors.
Turn on all bathroom and kitchen fans to depressurize your house.
Use a smoke stick to find drafts around walls, windows, and doors.
You worry about using expanding foam around windows and doors:
Use low-expanding versions of this foam that are specially designed for windows and doors.
You don’t have a caulk gun:
Use caulk packaged in a tube similar to toothpaste that you can squeeze by hand without using a special tool.
Borrow a caulk gun from your local library of things.
You are worried about your ability to seal leaks yourself:
Check to see if your local area has volunteer programs that help homeowners with weatherization and home repair.
Hire a professional company that specializes in weatherization and insulation.
You insulated before doing air sealing and weatherstripping:
If you are insulated with spray foam, that provides both air sealing and insulation.
If you are insulated with fiberglass, you may want to remove it, do an air-sealing project, and then upgrade to cellulose insulation.
You are worried about indoor air quality if you make your home too airtight:
If you burn fuel in a furnace, water heater, stove, or other appliance, consult with a professional.
If you do not burn fuel indoors, making your home more airtight and installing fans to allow you to control ventilation will improve your indoor air quality.
Consider hiring a professional to do a blower door test to determine your home’s ACH before making any major investments in mechanical ventilation.
Strategies and Goals
Energy
Increase energy efficiency
Reduce airflow that wastes energy
Increase insulation that saves energy
Milestones
Decrease how much energy you buy
Measure: How much electricity and fuel you buy
Method: Energy bills
Time Period: Year
Limitations
Caulk and foam insulation are made from fossil hydrocarbons.
Older buildings are difficult to make air-tight and well-insulated.
If you burn fuel inside your building, reducing airflow can create health and safety hazards.
Opportunities
Electrification 101: Heat-pump Water Heaters
Eliminating fuel-burning water heaters makes it easier and safer to reduce wasteful air flow through your building
Electrification 102: Electric Induction Ranges
Eliminating fuel-burning kitchen appliances makes it easier and safer to reduce wasteful air flow through your building
Electrification 103: Heat-pump Space Heaters
Eliminating fuel-burning heating systems makes it easier and safer to reduce wasteful air flow through your building
References
Articles
Keywords
energy, efficiency, air sealing, weatherization, insulation, airflow, heating, cooling