How Much Attic Insulation is Enough?


Most of the energy costs spent to keep a home warm in the winter and cool in the summer end up leaving through the attic. In the summer, the sun’s heat pours in through the attic and in the winter, warm air rises past the ceiling and out of the home. Saving on energy costs starts in the attic, but how much insulation is enough?

Insulation is rated by number denoting how much of a thermal barrier each type of insulation provides. The farther north one goes the higher insulation number needed. Cold weather states, such as the Atlantic north-east, mountain states, and northern Mid-west require an R-49 rating. Warm weather states in the middle latitudes call for R-40; Southern and Gulf States would require R-38.

These guidelines offer the answer to the question, “how much insulation is enough?”

Ratings Calculation

Insulation ratings are measured by thickens and material type. Fiberglass blown insulation provides R-2.5 per inch. For example, using fiberglass blown insulation for Houston attic insulation would require an installed depth of 15 inches. Loose cellulose blown insulation is rated at R-3.5 per inch which relates to 11 inches in the above example.

Any homeowner can determine the attic insulation rating with just a ruler. By measuring the depth of the attic insulation and comparing the material’s rating to the manufacturer’s data, an R rating can be quickly calculated.

How To Improve An R Rating

If the above calculation puts attic insulation below the recommended level, there are many ways to increase home insulation. Increasing the insulation in an attic a few points above the guideline can also decrease energy costs, but after more than a few points increase, the cost of insulation will be greater than the savings.

Blown insulation installed by a professional can easily increase the depth and R rating of an attic. This solution provides an efficient thermal barrier and easily integrates with existing insulation. A less costly solution is the use of fiberglass battes which can be laid down to quickly add depth. However, improperly installed battes can compress the material below and reduce the effective insulation rating.

A finished attic presents a more difficult challenge. It is often not practical to remove finished walls and floors in order to lay down more insulation. In this case, a radiant barrier is the perfect solution to increasing attic insulation. A radiant barrier is applied onto the ceiling and can be painted over. The radiant barrier acts as a reflective surface for heat, keeping the sun’s heat out in the summer and the home’s own heat inside during the winter, all without any remodeling required.

Adequate home insulation is the best way to keep a home comfortable while saving energy costs. With just a ruler, any homeowner can determine if they are meeting their insulation needs. With many options available to increase the insulation in an attic, no homeowner has to needlessly suffer through a cold winter, hot summer, or high utility bills.