Glass block windows, first developed in the early 20th century, are finding new appeal as a design element in the environmentally conscious 21st century. Once confined largely to use in foundation walls and bathrooms, designers are now utilizing glass and acrylic block for exterior walls in living and bedroom areas. They also employ the translucent building blocks as room dividers in interior walls.
Pro: Energy-Efficient Illumination
Glass block windows offer thermal insulation values that are similar to double-pane windows, but the cement mortar that holds them in place performs a better job of blocking air infiltration than traditional vinyl or aluminum window frames. That means that glass block windows never contribute to a drafty room. And because glass block windows can be used across a large expanse of exterior wall space, they provide ample amounts of energy-efficient daylight illumination indoors.
Con: No Natural Ventilation
Sick Building Syndrome describes a home that is so tightly sealed that unhealthy or toxic fumes cannot escape outdoors. That can be a problem when flooring is cleaned with harsh chemicals or when cabinets are refinished using foul-smelling, toxic paint strippers. And while traditional windows can open up to let fresh air into the house during temperate weather, glass blocks require homeowners to continue using their heating or air conditioning system to circulate indoor air.
Pro: Green Building Credits
Installing glass block windows helps a home qualify as a LEED-certified or Energy Star-certified building. Those certification programs confirm that a home is environmentally sustainable and energy-efficient while offering a value-added bonus: Green buildings have a resale value that's between 5 percent and 35 percent higher than comparable structures. Prospective home buyers looking at a green-certified structure that includes glass block windows can expect that their energy bills will be measurably lower than similar homes.
Con: Privacy and Structural Issues
Modern bathroom designers utilize glass blocks in both external walls and indoors for permanent room dividers or shower stalls. Unfortunately, glass blocks create privacy issues that are not easily resolved. A glass block exterior wall can be masked with all-season foliage, such as tall shrubbery or evergreen trees. Indoor solutions include color-tinted or frosted glass blocks. Glass blocks are also substantially heavier than conventional timber frame and drywall construction, so interior glass block walls require increased engineered support.
- Bangor Daily News: Glass-Block Windows Good for Security, Less Energy Efficient
- Colorado Energy: R-Value Table
- Quality Glass Block & Window: LEED Benefit From Using Energy Efficient Glass Block
- Door&Window.com: Block Glass Window Energy Efficiency
- Institute for Building Efficiency: Multiple Studies Document Green Buildings Add Value
- Home Design Ideas: Glass Block Showers – the Advantages and Disadvantages Having Glass Block Showers
- Ask the Builder: Glass Block
- Masonry Magazine: Architects Are Rediscovering Glass Block
Mike Matthews is editor of Green Building Product News, a national publication that covers sustainable innovations in building and remodeling, and he has spoken at national conferences on green building. He has also served as founding editor of "Paint Dealer" magazine.