Attic insulation depth chart

The R value of an insulating material is basically the temperature difference needed between its two sides to conduct 1 BTU of heat per hour through an area of one square foot per inch thickness.

R49 insulation rating means that it takes 49 Fahrenheit of temperature difference between its two sides to conduct one BTU of heat per square feet area of that insulation material.

The R-value of a material increases with an increase in its thickness.

Therefore, different types of insulating materials and their combinations can achieve R49, given they are thick enough to provide adequate thermal resistance.

How thick is R49 insulation?

Simply put, the thickness of R49 insulation varies with the type of insulation material.

Given below is a table listing the thickness required for different insulating materials to be R49.