What are the Insulation Properties of Glass Block Windows?

R-Value

• The R-value is the standard by which insulation is graded for efficiency. This simply means the thermal resistance of the material, or the rate at which it allows heat to flow through it. Heat will always flow from areas of greater heat to lower heat. When the temperature inside the home is higher than outside, the home will lose heat through the walls and roof. Increasing the R-value of the material slows down the loss.

Various Material

• The R-value of glass block varies according to the manufacturer and the way the block is constructed. The range for insulation value is somewhere between 1.75 and 2.0. For comparison, a batt of rock wool insulation is 3.38 and a batt of fiberglass is 3.16. Both blown rock wool and fiberglass are slightly lower. Pine wood siding is 1.28 and dry wall is 1.0. The R-value is accumulative, so a wall constructed of siding, insulation and dry wall would have the combined R-value for all material.

Natural Light

• Because glass block is not combined with other building material but stands on its own, the insulation value will be less than standard walls. Energy loss is mitigated by the blocks, allowing light to enter an area during the day, negating the need for supplemental artificial lighting, which uses electrical power. Replacing a regular glass window with glass block raises the overall R-value.

Drapery

• Glass block windows gain insulation value with a drape that is closed when the window is no longer needed. Keeping the curtains open when the sun is out allows the maximum solar energy to filter through the blocks, and closing them at night prevents the warm air from flowing back out. A windy day can draw the heat from the windows much faster, so close off the curtains when the wind picks up.