What are they? R-5 windows are windows which meet the energy savings standard of .22u value for operating windows and .20 u value for fixed windows. Most manufacturers are working on getting their windows to qualify. Some have already reached this level.
Vinylmax has reached the R-5 standard with the Easton window by adding triple pane glass with double low-E and argon.
Why do we want R-5 windows? They are more energy efficient. This will lower our need for energy to heat and cool our homes.
More to come on R-5 as the EPA sets up the new Energy Star standards.