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Attic insulation: what the R-value really does

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1R-value is a measured resistance, not a marketing term

R-value measures how well a layer of insulation resists the conductive flow of heat; the higher the R-value, the more insulating the material is, and higher R-values reduce heating bills in cold weather and cooling bills in hot weather alike.

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2Insulation is near the top of the list for a reason

When ranking energy projects by benefit versus cost, adding insulation is often at the very top of the list; only sealing large air gaps in a home usually comes close to matching its return.

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3The cooler analogy is the whole concept

A foam picnic cooler keeps ice frozen far longer than a plastic bag because the foam resists heat moving from the warm outside to the cold inside; attic insulation does the identical job for an entire house, at a much larger scale.

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4R-value per inch is the number that lets you compare materials

Because R-value adds up with thickness, the honest way to compare insulation is per inch: a standard fiberglass batt runs about R-2.9 to R-3.8 per inch, loose-fill cellulose R-3.4 to R-3.7, extruded polystyrene board R-4.5 to R-5, and unfaced polyisocyanurate board R-5.6 to R-6.3; Missouri's extension recommends R-49 for ceilings and attics, which at batt numbers is well over a foot of material.

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5Half the bill is the part insulation touches

In a cold-climate state like North Dakota, about half of all the energy a home uses goes to heating and air conditioning, which is the slice of the bill that attic insulation actually moves; the other half, lights, water heating and appliances, doesn't care how deep the attic is.

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