One of the "low-hanging fruits" (i.e., easy and relatively inexpensive with
a high return for the investment) is installing insulation. Homes built before 1978
are unlikely to have insulation in the walls or underfloor area (if present). Insulation
installed in attics 25 or 30 years ago may have settled, been crushed or displaced by
workers, or even contaminated by animal intrusion. Older homes may not even have
any attic insulation.

Installing insulation in the attic is usually easy. The insulation can either be installed on
the "floor" of the attic, or even on the underside of the roof.

Insulating walls is more involved unless done in the course of a remodel, where walls are
opened up or interior repainting or a new exterior is involved. Usually, we drill small holes
(about the size of a quarter) and blow in insulation through each hole. Because of the structure,
we have to drill a lot of holes. If the walls are opened up, a number of options and materials are

There are many different kinds of insulation and ways of installing it.

Here are some typical insulation types and characteristics:

R value/inch Cost/sq. ft. Method of Application
Cellulose 3.0 - 3.8 Low to medium Loose, Dense-Pack, Spray, Encapsulated
Fiberglass 3.1 - 4.3 Low to medium Batt, Loose, Dense-Pack, Encapsulated
Open-cell SPF 3.6 Medium Spray
Closed-cell SPF 5.5 - 6.5 High Spray
Cotton 3.7 Medium Batts
Expanded Polystyrene 3.7 - 4.0 Medium Rigid Board
Extruded Polystyrene 3.6 - 5.0 Medium Rigid Board
Polyisocyanurate 5.5 - 6.8 Medium Rigid Board
Cementicious Foam 2.0 - 3.9 High Spray
Tripolymer Foam 5.1 High Spray

These R-values measure the degree of heat transmission through the material. They do not account for effects of air infiltration, which can increase heating and air conditioning costs as much as 40% (!!). That is why we ALWAYS recommend air sealing in conjunction with insulating.

Another consideration, especially in walls, is thermal bridging. This reduces the effectiveness, and overall insulative value, of a wall because wooden (or steel) structural members surrounding the insulation conduct heat relatively well (R-value for wood is about 1). A continuous layer of insulation board on the outside of a wall will give better overall insulation than a slightly higher R-value insulation between wooden studs 16" apart.


Fiberglass batt insulation is the most common type of insulation because it is one of the cheapest. It has usually been installed poorly or improperly. Defects in its installation can significantly reduce its effectiveness. Worse, fiberglass batts that are faced with kraft paper and installed in the attic with the paper side up can create a potential fire hazard. The 2008 California Energy Code (effective January 1, 2010) requires proper installation, perhaps even inspected carefully and signed off on.

Insulation contractors are in a competitive business, and their low bids do not allow for the significant amount of labor required for proper installation. Batts must be in contact with the air barrier and the surfaces on all six sides (five if on the attic floor or knee walls) to work properly. If there are any pipes or wires in the space the insulation has to occupy, the batt must be cut and installed around the obstruction to maintain that contact. This is a lot of work. The bats have to be cut to size for the (usually) many off-standard size cavities they have to fill completely, maintaining the five-or-six sided contact. A one-inch gap is much too much. More work. RESNET (Residential Energy Services Network) estimates that R-38 batts with 2% voids is only as effective as R-22. Manufacturer Owens-Corning found that double R-19 batts (R-38) laid in their laboratory attic with standard truss construction measured only R-25.6. Presumably, these were well-installed.

Fiberglass batts do not offer any resistance to airflow, if there is no air barrier or a less-than-fully-effective one. And in those cases, fiberglass particles could enter the breathing air of the house.

Fiberglass batts only work well in airtight walls when 99.5% properly installed. Attics have to be similarly air-sealed with 99.5% proper installation for good performance. Although there may be a lower initial cost, the total cost over the complete life cycle may be higher when you include the additional heating and air conditioning costs.


Loose fiberglass fibers can be sprayed into a wall or into an attic. They can be applied at different densities. Installation quality can be much better in attics because it flows around and over obstructions, insuring contact with all sides. In new construction, a net is installed over the studs in the open wall, and the fiberglass is sprayed in through a hole in the netting. Dense-packed fiberglass can provide some restriction of airflow, and a newer product (Johns-Manville "Spider") claims to airseal better than cellulose. Sprayed fiberglass (usually dampened with a binder) attenuates sound better than batts, and performs better due to inherently better installation quality. Of course, it is more expensive than batts

Still, to be effective, a good air barrier is necessary. Without it (and possibly, even with it) some fiberglass fibers can get into the breathing air.


Cellulose is a versatile product that can be installed in attics or walls. It is made from recycled newspapers with a fire retardant, and is unfriendly to insects and rodents. Its performance has been improved considerably from an inferior product in years past to one of the better products, preferred in many applications. It also is efficient to manufacture, with a low "embodied energy" of 600 BTU/sq. ft. of R-20 (compared to 4,500 BTU/sq. ft. for fiberglass and around 14,000 BTU/sq. ft. for spray foam and EPS). This makes it a particularly "green" material, along with its use of recycled material and non-toxic chemicals.

In attics, it can be blown in to different depths, and goes around obstructions to achieve the required contact with all adjacent surfaces. The cellulose packs to a certain (controllable) extent to provide some air sealing. It also settles over time, which should be taken into account by the installer to provide a written guarantee of settled depth.

Cellulose can be installed in walls in existing houses. This requires drilling a hole about the size of a quarter in either the interior or exterior wall (or removal of some of the exterior siding if possible), through which a tube is inserted to blow in the cellulose. The holes are sealed, and the wall is repainted or otherwise repaired. In new construction, a damp cellulose mixture with a binder can be sprayed into the open stud bays, and when it dries, the excess is cut off flush with the studs (and recycled). This gives excellent results when done properly. For dry applications, a polyethylene material is applied over the studs, and the material blown in through a hole in the film. This technique provides a vapor barrier as well as allowing confirmation of void-free installation.


Batts of recycled cotton materials (mostly denim), usually pre-consumer manufacturing wastes, have become available and popular recently. The batts are available in R-13 (for 2x4 walls) and R-19 (for 2x6 walls or attic floors), and some other thicknesses. Many contractors find that the batts are difficult to cut in order to fill in gaps; care must be taken to make sure that this does not result in poor installation.


These foams are made from equal quatities of two parts, which are mixed in a spraying nozzle in the process of applying them; they react chemically to expand and quickly set. One material is a polymeric isocyanate (a petroleum derivative), and the other is a mixture of a catalyst. surfactants that determine whether the material develops closed or open cells, fire retardants, blowing agents to create the foam bubbles, and polyols (chemicals that can be either petroleum based or derived from soy). Only 5% to 15% comes from soy or recycled plastics; that is the extent of the "green" in the claims of the "green" foams.

Although these foams have some excellent characteristics that make them quite useful, worker protection is necessary during the installation of the foams, as toxic materials are released--but they quickly dissipate. Some experts (not most) are doubtful about the long-term safety/toxicity of these materials. The formulations are complex and proprietary.

SPFs can be either open-cell or closed cell.


The open-cell sprayed polyurethane foams have a low density, about 1/2 pound per cubic foot. When they are sprayed on, they expand to 100 times their liquid volume. The structure is a maze of tiny bubbles, and the still air within the structure creates the insulative value (same as fiberglass). Since the foam expands to fill the cavity and adheres to the adjacent structural members, it is more effective as an air barrier than conventional blown cellulose or fiberglass. Open-cell foams are soft when they cure. It is not a good vapor barrier; moisture can pass through.


The closed-cell SPFs are medium-density foams, about 2 pounds per cubic foot. The ingredients expand to about 20 to 30 times their liquid volume, and cure to a hard material. The tiny bubbles that form in the foam are closed, separate from each other. The R-value depends on the blowing agent (the gas that is trapped in the bubbles); these are proprietary among the various manufacturers. The cured foam is rigid and strong, adding to structural values, and it is relatively impermeable to vapor. It is excellent for both airsealing and insulating at the same time.


This foam is not used much. It is a cold-setting foam, meaning that it doesn't expand once it leaves the tube. It can shrink about 1%, so that it can leave voids.


This is a powder that is mixed with water on site and injected into cavities. The old formulation of urea-formaldehyde foam was good insulation except for (1) it offgassed formaldehyde for quite a while at levels which created serious health problems (2) when it got wet, it emitted more formaldehyde.


This is a special-purpose. lightweight material made from magnesium oxide, silicates, and calcium salts. It has no petrochemicals, and has to be cut with a saw. It is not a vapor barrier, and can crack and come loose. But it is fireproof, so it may be specified for this reason.


Rock wool is a mineral wool, manufactured like fiberglass: the mineral (iron slag, a waste product from iron manufacturing) is melted and spun into fibers. It has been around since 1934. It is fireproof, does not support mold or mildew growth (although dirt on the material can be mold food), and is not carcinogenic. It is available either in batts like fiberglass, or as a loose fill.



Money Saving Tip:

Tune up your heating and air conditioning system.
Regular maintenance can lower your operating costs and
extend the service life of your equipment. And do you
change your air filters regularly? Use a programmable
thermostat? Taking small steps such as these can
make your wallet as well as your home greener.

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