America's Insulation Experts


How Does Insulation Work?

Insulation creates resistance against heat that moves by way of conduction-moving from molecule to molecule through solid materials. The resistance comes from billions and billions of microscopic air pockets. Molecules in air pockets are farther apart than in solid materials, so the transfer is slowed.

Where should insulation be installed?

Insulation is part of the thermal barrier around the area of a home that is heated and cooled. Usually, that’s the exterior walls around the living space, any knee walls in an attic, and the attic or ceiling above the upper living area.

How can the exterior walls of homes be reinsulated without removing the interior walls?

Products like injection foam can be inserted into wall cavities through the exterior of most homes. The exact method will vary with different types of siding. Occasionally, it is advantageous or necessary to inject through interior walls.

Should a garage ceiling be insulated?

Not unless the garage is heated. Insulation is used to keep heat from either leaving or entering a conditioned space. If a garage is not heated, insulating its walls and ceiling will not make the garage any warmer.

How much insulation should there be in an attic?

The U.S. Department of Energy recommends a minimum resistance rating of R-49 for our climate zone. That amounts to approximately 18 inches of blown-in fiberglass insulation.

Which is better to use in an attic-blown-in insulation or fiberglass batts?

Blown-in insulation goes everywhere, fills every space easily, and creates an even and continuous blanket of resistance. The primary problem with batts is that almost no one installs them correctly because they aren’t aware of the proper method. Also, installing batts correctly is very labor intensive, and few people are willing to spend the extra time.

What’s the difference between insulating and air-sealing?

Insulation creates resistance against conductive heat transfer, while air-sealing stops air that is moving by way of convection (moving air). Think of insulation as the wool sweater you put on to keep warm indoors, and air-sealing as the windbreaker you put on to keep warm outdoors.

Why is air-sealing a ceiling so important?

Air-sealing is regarded as one of the most cost-effective ways of improving the comfort and energy efficiency of a home. Stopping air leakage in a ceiling is crucial for three reasons: (1) It’s one of the easiest areas of existing home to access; (2) It reduces the “stack effect” of air flow through the home; (3) It improves the efficiency of the insulation.

What other areas of a home should be air-sealed?

The greatest amount of air leakage in a home actually occurs in the basement, around the rim or band joist. Unfortunately, if a ceiling is installed in a basement, it is impossible to access the rim joist without removing the drywall.

Why are rooms over a garage cold?

Most garages are not heated. Cold air from the unheated area gets into the cavities between the garage ceiling and the subfloor of the rooms above. Often these cavities have been filled with a type of insulation (like fiberglass) which is designed to stop conductive heat loss rather than convective air movement. Consequently, the cold air moves right through the insulation. The subfloor can either be air-sealed with spray foam, or the floor cavities filled with injection foam to prevent the cold air from circulating.

How should attics be ventilated?

Ventilation requires two elements-air intake and air exhaust. Air intake is the most important, and it should come from the soffit area. The exhaust vents should be at or near the highest point of the roof, in the form of individual openings or a ridge vent.

Why are baffles important for proper ventilation?

Baffles create space between the roof deck and the insulation in the attic, allowing air from the soffit to flow along the bottom of the roof deck and out through the roof vents. Baffles also help prevent wind from eroding insulation over the ceiling around the perimeter of the home.

What is “wind erosion” in an attic?

Wind erosion occurs when air flow from soffit openings pushes loose insulation away from the top plate of the exterior wall and the ceiling around the perimeter of the home. This may contribute to icicles on gutters or ice dams. Wind erosion can be corrected quite easily.

How many baffles should there be in an attic with soffits?

Since air intake is the most important aspect of ventilation, we want to maximize the amount coming from the soffits. This is best accomplished by installing baffles in all the rafter cavities that connect to an open soffit.

Why are powered roof fans a bad idea?

Unless the ceiling area of a home has been thoroughly air-sealed, electrically-powered fans can literally suck the air out of a house. Avoid these types of roof vents!

What causes frost in an attic?

Frost develops in an attic when moisture-laden air gets into the area. When the moist air comes in contact with the cold roofing nails and roof deck, it condenses in the form of frost.

What problems can result from frost in an attic?

Frost itself doesn’t do any damage, but once it melts, damage can occur. Melting frost can lead to water stains on the ceilings, wet insulation, mold and a deteriorated roof deck. Obviously, none of this is good, which is why you do not want frost in your attic.

What are the sources of the moisture that leads to frost?

The more humidity a house produces, the more frost there will be in the attic. Homes with the worst frost problems almost always have a whole-house humidifier attached to the furnace. Extra humidity can also come from hot showers, aquariums, cooking, washing clothes, and even from having a lot of houseplants

How does moisture get into an attic?

Moist air usually gets comes from air leaks, or attic bypasses, between the attic and the living space below. The ceiling of a home is supposed to be an air barrier between the attic and the living area. Unfortunately, virtually every home is built with hundreds of areas of leakage, both large and small. Having HVAC ducts in the attic-combined with a humidifier on the furnace-can lead to major frost problems.

What can be done to reduce frost in attics?

Sometimes it’s as simple as reducing the excess humidity by turning off a humidifier. However, it’s also a good idea to have the ceiling air-sealed, not only to stop the flow of moist air, but also to improve the overall efficiency of the home.

What is a knee wall in an attic?

A knee wall is any interior wall that backs up to attic space. It is the equivalent of an exterior wall, which means it must be both insulated and sealed properly. Almost all knee walls in homes more than 10 years old are neither insulated nor sealed correctly.

How should knee walls be insulated and sealed?

The insulation in the knee walls cavities must be in contact with the drywall, and there should be an air barrier covering the cavities on the attic side of the wall. The easiest way of insulating and sealing a knee wall is by applying a 2-3 inch layer of closed-cell spray foam.

Why are most basements cold?

There are various reasons why basements are cold: (1) It’s the level where the coldest air in the home settles, because it’s also the heaviest and densest air; (2) Heated air delivered to a basement-which is lighter and less dense than colder air-is delivered at the ceiling level, where it stays; (3) Concrete floors and walls can wick moisture from the surrounding soil, making the walls and floor feel colder; (4) Unlike other areas of the home, the basement never benefits from solar heat gain; (5) The rim joist area can leak a lot of cold air, especially in the winter.

Should basement walls be insulated?

The portion of the basement wall that is above grade is about the only area that really needs insulation. For the walls that are below grade, insulation can help make the walls “feel” warmer, but that’s more of a psychological benefit than anything else.

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