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## How is R-value calculated?

R-values can be calculated by **dividing the thickness of a material (in metres) by its thermal conductivity (k-value or lambda value (λ) in W/mK)**. R-values are therefore expressed in m2K/W (or ft2·°F·hr/Btu in the USA).

## What is the R-value of a hollow core door?

Here is a simple chart to help understand how R-value is calculated for windows and doors:

WINDOWS | R-VALUE |
---|---|

DOORS | R-VALUE |

Wood Hollow Core (1-3/4”) |
2.17 |

Solid Core Flush (1-3/4”) | 3.03 |

(2-1/4”) | 3.70 |

## What is the unit of R-value?

The R-Value is an **imperial system unit of measurement (ft ^{2}·°F·h/BTU)** and the RSI Value is a metric system unit of measurement (m

^{2}·K/W). The higher the resistance value, the slower the rate of heat transfer through the insulating material.

## What is the R-value of 5/8 drywall?

Tables of Building Material R-values

Material | Thickness | R-value (F° · sq.ft. · hr/Btu) |
---|---|---|

Building Board | ||

Gypsum Wall Board | 1/2″ | 0.45 |

Gypsum Wall Board | 5/8″ | 0.5625 |

Plywood | 1/2″ | 0.62 |

## What Windows R-value is best?

A good R-value range: **Greater than R-5**. A good U-value range: 0.20 – 1.20 according to energy.gov.