Air sealing is like putting a windbreaker around your building and insulation is the sweater under it to keep warm when the temperature drops. Insulation works by slowing down the indoor air that you spend money to heat or cool as it travels to the outdoors. Properly insulating your building may not only reduce heating and cooling costs, it may also improve comfort. Insulation's effectiveness typically depends on the material used, how much of it is in place, where it is installed, and if the building has been properly air sealed. For example, fluffy insulation may work great where there is no air flow, but do little if the area is drafty or unsealed. Insulation that is settled in wall cavities can leave spaces for cold air and moisture to flow, while properly installed insulation usually fills these gaps.
Insulation’s ability to reduce heat transfer is rated in terms of its “resistance,” or R-value. Although Vermont’s Building Energy Standards require certain insulation levels for newly constructed buildings, some existing Vermont buildings have very little or even no insulation in walls, ceilings and basements. More information on the Vermont Building Energy Standards is available on the Department of Public Service website.
For optimal energy efficiency, it is usually recommended that the entire building envelope be air-sealed and insulated from top to bottom, including attics, cathedral ceilings, all wall cavities, rim joists, basement walls, and crawl space walls. For spots that are harder to access, it may be more cost effective to stage upgrades until another improvement project opens those areas of the building. Types of insulation materials vary, and their characteristics typically determine their best use. Common insulation materials include:
- Fiberglass: Glass spun into long fibers and woven. Sold as big rolls or batts and comes with or without vapor retarder (a material that reduces the rate at which water vapor can move through a material) facings, such as Kraft paper, foil-Kraft paper, or vinyl. Often installed in the cavities between wall or floor joists.
- Cellulose: Recycled newsprint that is finely shredded and chemically treated to resist fire, corrosion, fungal growth, and vermin. Often sprayed into wall cavities and attics.
Foam board: Made from a variety of petroleum products and formed into stiff sheets, with or without foil vapor retarders. Installed both indoors and out.
Spray foam: Made from a variety of petroleum products that change from liquid under pressure to solid when applied. Isocyanates, a main ingredient in many spray foams, can cause asthma, sensitization, lung damage, skin and eye irritation and respiratory and breathing problems. Exposure can occur through contact with vapors, aerosols, and dust created during and after application. California has banned spray foams with unreacted methylene diphenyl diisocyanates (MDI). Spray foams are available that contain safer chemicals than MDI. Look for spray foams that do not list MDI or other isocyanates in the ingredients, or other materials listed above. If spray foam containing MDI or other isocyanates must be used, make sure to hire a trained spray foam applicator, such as a Spray Polyurethane Foam Alliance certified applicator.
Learn more about health risks from spray foam and tips about how to install it safely at the EPA Safer Choice webpage.
Some Benefits of Insulation
Reduced energy demand – Effective insulation typically means that it takes less heating and cooling to make your building comfortable and reduces heating and cooling demand, regardless of what fuel(s) you use to heat and cool your building.
Increased comfort – Insulation projects typically make rooms warmer in the winter and cooler in the summer. Increased insulation levels may also reduce outside noise, making your building quieter.
Sound investment – Insulation projects may provide cost savings for decades.
Health and safety issues (e.g., old wiring, mold, etc.) should be addressed before insulation is removed or added
Insulation is typically most effective when done after air sealing
It’s important to choose the material that is most appropriate for each part of the building
Rebates or tax credits for insulation work fluctuate and may only be available for a limited time or limited time each year. (Consult your accountant or tax professional about your specific tax situation.)
Some Next Steps
Consulting with a trained energy auditor is typically the best way to determine what insulation materials will work best in your building, as well as to discuss indoor moisture or other health and safety concerns. Like all your energy decisions, whether to add insulation will depend on your budget, building improvement goals, and how much you are likely to save over time.
Visit the ENERGY STAR® website to learn more about sealing and insulating.
The EPA's Rule Your Attic! page has an entire section on insulation, including information about how to check if your insulation measures up.
Visit the pages below to learn more about Weatherization: