ROOF INSULATION
Vital foam-roof upgrades add comfort, lower
utility bills, and enhance your home's value

By Randy Feriante

In December 1955, Eichler owner Bob Johnson paid only $12 to heat his home. Back then, original Eichler roofs had less than an inch of fiberglass, flattened under a heavy load of tarpaper and thick gravel.

For many occupants, this small amount of insulation wasn't enough; inside, candles were known to melt in the summer heat, and steamy breath fogged the air on cold winter mornings.

Utility bills are much higher now, even after inflation is taken into account, but fortunately technology has become available over the years to help Eichler owners save money. Thanks to improved ceiling insulation, an Eichler can be transformed from the least comfortable summer or winter residence to a haven of energy-efficient comfort, and a quiet one as well.

Roofing systems, including tar and gravel, sprayed foam, torch-down, and single-ply, now use two forms of the same generic polyurethane foam roof insulation material. As an insulator, polyurethane foam, whether 'board-stock' or 'sprayed,' has been transforming Eichlers for three decades. Insulation must be installed when re-roofing, not as an afterthought.

Most insulation materials -- fiberglass, cellulose, and rock wool are common examples -- rely on trapped air to slow temperature changes. The level of effectiveness dramatically improved when polyurethane foam became available. A cubic inch of poly foam has approximately one million tiny cells. Board foam traps air better than fiberglass and is a better insulator.

However, sprayed foam has an a 20 percent higher R-value than board foam of the same thickness. The cells of sprayed foam are closed, trapping an inert gas that insulates better than any material available today. Those cells also enable spray foam to be used to waterproof. To understand R-value, first consider that one inch of wood equals R-1. Thus, an R-19 roof assembly will behave thermally as though the ceiling was made only of wood that is 19 inches thick. R-19 is a good target for any Bay Area Eichler. This can save 25 to 40 percent on heating costs over a poorly insulated roof.

Installing insulation on Eichler roofs beyond R-19 may not be practical. Occupants may not notice any added insulation benefit, and the additional cost could take decades to recoup. Generally, an insulated tar or torch-down roof is comparable in cost to a sprayed foam roof. An insulated single-ply roof is usually the most expensive.

On a roof, reflecting heat is good, absorbing heat is not. The newest version of the California energy law called Title 24 will soon require changes in most roof systems, and in fact require reflective roof coating on most new roof installations beginning October 2005. For now, low-rise homes, which would include most Eichlers, are excluded from this energy-saving requirement. Sprayed foam roofing already surpasses the Cool Roof and Energy Star requirements, which have become desirable industry benchmarks.

For example, on a 90 degree summer day, a non-reflective Eichler roof surface can reach 160 degrees. Board insulation must prevent this extreme heat from getting inside by keeping it in the roof assembly. Heat builds up and cooks the roof system, shortening service life. On the other hand, the white reflective surface of a foam roof only reaches 110 degrees on the same day. This 50 degree difference makes insulating the Eichler much easier. Spray foam has the unique ability to insulate on the very outside layer, and avoid undesirable 'heat-sinks' (gravel) or 'short circuits' (fasteners).

When placed on the outside of the building envelope, the first one inch of sprayed foam is able to achieve 80 to 90 percent of the insulating effect. (As a side note, the space shuttle uses one inch of uncoated spray foam to insulation its large, brown stainless-steel fuel tank that is 300 degrees below zero.)

Foam boards are factory made in four-by-eight foot panels in various thicknesses. They are fastened to the wood using long nails with large square heads, long screws, or sometimes even adhesives. Boards should be well secured, especially to avoid problems since it's possible for their size to change with age (typically they shrink) up to four percent. A tar, single-ply, or torch-down roofing membrane is then installed on top.

Foam boards insulate well, but one recent study has shown that a rooftop foam board assembly can lose up to 25 percent of its effective insulation value because air can move in the gaps at the electrical and around board edges. Foam boards insulate better when their edges are taped, and multiple board layers are more effective when the top layers are installed in a staggered fashion over the ones below. This layering is seldom carried out, since it could add considerable expense for labor and material to the installation for the same R-value of insulation.

Foam boards must be protected during installation. They are not designed or manufactured to be waterproof and can absorb water. If they are left outside overnight, their surfaces can get damp and lead to immediate and even severe warping. Warped boards should be discarded. Foam boards are very light and can be used, with a degree of success, to build up areas that collect water. This built-up method is much preferred over adding gravel to cover standing water.

It is not uncommon for membrane roofs to fail at the point where the insulation boards end and the overhang begins. A noticeable height difference can be clearly seen at this junction. The bending of roof membranes is less a problem than the expansion and contraction differential. Heat and cold are absorbed by the roof and gravel and forced to remain in the roof by the foam insulation. While one inch away, where there is no insulation, heat easily soaks through the overhang. This narrow line of roof membranes takes a constant beating.

Most roofing and insulation is made in a factory, and then installed by roofers. Sprayed foam is manufactured by the same workers that are installing it. Think of it as 'real-time' roofing. When choosing a spray foam contractor, proven ability to install durable roofs is paramount; a small, hidden mistake can later cause serious roof problems or failure. Sprayed foam fits exactly and adheres well to a cleaned surface. When applied, it rises in three seconds and solidifies in one minute. Foam is sprayed to a thickness that reaches the desired R-value, adding almost R-7 per inch. Low areas can be carefully built up with additional waterproof foam insulation. Additions and modifications are incorporated without compromising the original roof.

Cleaned tarpapers and other roof membranes make an ideal base for sprayed foam. This helps avoid the expense accompanying thousands of pounds of landfill from each roof replacement. Instead of being discarded, existing foam boards can remain in place and continue to contribute to energy savings. Clean gravel removed from roofs can be recycled.

Even though windows should not be overlooked in discussions of heat loss in an Eichler, they are secondary to the roof. After all, the biggest feature on any Eichler is the roof. Inside the house, underneath that huge surface, heated or cooled air constantly cycles at the ceiling. It continually costs real money and comfort as this treated air changes back to the outside air temperature.

When it's time to re-roof your Eichler, consider insulation. It will enhance your home's value and improve your quality of life.

See other Eichler House Doctor stories