Ventilation is a key aspect of any insulation installation. The more air tight an area becomes the less fresh air is circulated. A completely sealed new construction home will typically have an air to air exchanger bringing fresh air into the system from an exterior source. Current building codes require this but most existing dwellings are grandfathered and do not have such an exchanger. In these existing homes the air which comes in through air leaks around windows and openings under the siding of the home deliver sufficient fresh air.

Ventilation in attics is especially important due to the heat of attics in summer. Insulation on the attic floor is always a good idea while insulation on the walls or ceiling may only trap moisture and heat, and have a negative effect. In existing homes I recommend an inspection by a Building Performance Institute expert to assure that insulation leaves sufficient fresh air ventilation..

Insulation Materials

Insulation is measured in R value which vary from R1-R49. The higher the R value, the better your walls and roof will contain heat. Rolls and batts are made from fiberglass and rock wool and come available in sizing for standard spacing of wall studs.

Go green with old bluejeans. Global Keepers pick! This option for insulation has a value of R-30 for attic insulation 8” thick, according to Green Depot in Brooklyn, who will deliver it for $20. It does not need protective gear for installation and comes in batts sized for standard joist openings.

Cotton insulation is treated with the same fire retardant as cellulose insulation yet is 85% recycled material. One product uses recycled blue jean material. The remaining 15% is a plastic material. Cotton insulation is non toxic, according to the US Department of Energy and can be installed without skin or respiratory protective equipment. The product uses minimal energy to manufacture since it is made of recycled material yet costs 15-20% more than alternatives. While the material costs more than alternatives it can be installed by a homeowner. The R value is 3.4 per inch, according to the US Department of Energy*.

Fiberglass has been associated with health threats as during installation small particles may be released. Care should be taken during installation. Fiberglass is commonly used because it comes readily available in widths spaced for studs and can be purchased locally at reasonable cost. Fiberglass insulation is an air barrier. The R value ranges from R2-R3.75 depending on the density of the material.

Rock Wool is a man made material consisting of natural minerals. It contains an average of 75% post-industrial recycled content. It does not require chemicals to be fire resistant and comes in batts and rolls. Insulation capacity can be as high as 3.7 per inch, according to the Department of Energy*.

*US Department of Energy

Cellulose insulation is a type of loose fill insulation made from recycled wood fiber, primarily newsprint. It provides thermal resistance of R3.6- R3.8 per inch according to the US Department of Energy*. Chemicals are added to the material to make it fire and insect resistant. This insulation is usually installed with a hose and is not typically a do it yourself project.

Foam Insulation is a more expensive alternative to fiber but is very effective in buildings with space limitations and has an advantage in that it does not hold moisture. It is also an air barrier as well as a thermal barrier.

Insulation value may be in the R9 range per inch after installation but settlement within the first two years may reduce it to R-7 per inch*, according to the Department of Energy. The foam expands into the space and is easy to blow into small crevices. In addition, it does not hold moisture. The material contains a low conductivity gas (usually hydrochlorofluorocarbons or HCFC). There are other types of foam insulation beside polyurethane which are currently being researched for this site.

Outlets, high hats and sill plates are typical areas fro air infiltration. Use foam in such places to lower air infiltration if you have an air leaky house.

Local architects and a Building Performance Institute contractor expressed strong preference for cellulose and foam insulation as opposed to fiberglass, and positive results from use of cotton.

Air Barriers and Thermal Barriers

Foam insulation has the advantage of being an air barrier as well as a thermal barrier. This means it keeps cool air from coming in as well as preventing heat loss. Fibrous insulation is only a thermal barrier, not an air barrier.

Vapor Barriers

Moisture from the warm air in the home can permeate floors and ceilings and reach the exterior envelope of the home. If this happens, condensation will occur where the moisture meets the cold surface exterior and the cold vapor can freeze, causing peeling of paint and damage to insulation.

This can be prevented by the use of vapor barriers installed on the warm side of the insulation. The barrier should be, therefore, on the inside in a basement and on the downward side in an unfinished attic floor. In the course of engineering inspections in the sale of real estate, I have seen numerous instances where the insulation was installed with the vapor barrier on the wrong side. Various types of insulation come with the vapor barrier affixed.

For more information on Insulation also see the Department of Energy site