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Glossary Science & Engineering

R-value

R-value measures a material's resistance to heat flow; a higher R-value means better insulation.

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In more detail

R-values of layers add. Heat loss is area × temperature difference / R: 100 ft² of R-13 wall with a 40 °F difference loses 307.7 BTU per hour. Imperial and metric R-values differ by a factor of about 5.68.

Try these tools

Insulation R-Value Calculator

Add up the R-values of your wall or ceiling assembly's layers to find its total R-value.

See also

  • Glossary BTU
    A BTU (British thermal unit) is a unit of heat energy; BTU per hour measures the heating or cooling power of equipment.
  • Cheat sheet Home Project Estimating Cheat Sheet
    Volume, paint, drywall, board feet, roof pitch, stairs, fence, pool and insulation formulas with worked examples that match the calculators.
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