For years, the U.S. Department of Energy (DOE) has recommended R-30 and R-38 insulation for ceilings in U.S. homes, depending on the climate and the source of heat. Generally, the colder the climate, the more insulation they recommended.
DOE also recommended higher levels of ceiling insulation in homes heated with electric heat, which is of course the least efficient and hence the most expensive way to heat a home. Even so, DOE never recommended more than R-38 — even in the coldest climates.
Despite DOE’s long-standing guidelines, many of us who are interested in building super-efficient homes have been recommending to our clients, including architects and builders, that they install much higher levels of ceiling insulation — R-50 to R-60 in most climate zones. In really cold climates like that of North Dakota and northern Idaho we’ve been recommending even higher levels — from R-70 to R-80.
Many conventional architects and builders I’ve spoken to over the years have viewed such recommendations skeptically, and for good reason. One reason is that they, like all the rest of us, have been told that there’s a point at which additional insulation results in diminished returns. Why spend more money for marginal returns?
What architects and builders haven’t been told is that some forms of insulation lose their R-value over time. R-value decreases, for example, if a loose-fill insulation settles. In addition, tiny amounts of moisture accumulation can dramatically lower the R-value of many forms of insulation. Architects and builders haven’t been told — and haven’t come to this realization on their own — that the point of diminishing returns shifts upward as energy prices increase.
North America has been blessed for many years with inexpensive energy. Those days are over and energy prices are only bound to increase.
Bottom line, then, rising energy costs dramatically shift the economics of insulation. The old rules no longer apply. Fortunately, many enlightened architects and builders are beginning to adjust their practices to reflect this new reality. Even the DOE has increased its recommendations as you can see from the table below and in this link to their insulation recommendations.
Contributing editor Dan Chiras is a renewable energy and green homes expert who has spent a lifetime learning life’s lessons, which he shares in his popular blog, Dan Chiras on Loving Life. He’s the founder and director of The Evergreen Institute and president of Sustainable Systems Design. Contact him by visiting his website or finding him on Google+.