Posted by: glassblockblogger | December 30, 2011

Let’s Discuss General Design Considerations for Glass Block

Design Criteria for Glass Block
New York, New Jersey, Boston, Philadelphia

Eastern Glass Block 4 by 4 by 4

4"x 4"x 4" Glass Block from Pittsburgh Corning

If you are considering a Glass Block project, you may be having questions about height, load support, and anchoring guidelines for your project. So, let’s review some information from a leading glass block product manufacturer, Pittsburgh Corning Glass Block.

According to Pittsburgh Corning Glass Block, assuming a normal design wind load of 20 PSF (about 88 mph wind) and based on using our Premiere series (3 and 7/8 inch thick) glass block products, the maximum exterior size panel should not be larger than 144 square feet with limiting dimensions of either 20 feet in height or 25 feet in length – without exceeding the maximum area of 144 square feet per panel. There is a 2.7 safety factor incorporated within this criteria.

For areas of glass block larger than 144 square feet, the use of structural columns and/or shelf angles must be used to sub-divide these areas. For long horizontal expanses, structural columns or mullions (stiffeners) must be used. For vertically high expanses of glass block, the use of horizontal supporting shelf angles must be used to maintain the maximum area recommended and to stay within the dimension limitations stated above.

The maximum area of interior panels should not be greater than 250 square feet with similar limiting dimensions per panel of either 20 feet in height or 25 feet in length.

Glass block must be used as a non-load bearing material. All construction above glass block panels must be independently supported. Individual glass block panels must be isolated within their openings with expansion strip material at head and jamb locations with no loads imposed on the glass black panel. Glass block panels are mortared at the sill. Sills should be coated with a water based asphalt emulsion prior to laying the first course of glass block.

Installed weights of glass block walls are 20 pounds per square foot of wall area for Premiere Series blocks; 25 pounds per square foot for Thickset 60 Series block; 30 pounds per square foot for Thickset 90 Series (thick-faced) block; and 40 pounds per square foot for VISTABRIK® and solid glass block units. All structural members supporting glass block construction must be designed and sized for maximum deflection of L/600.

For exterior applications the building codes allow the use of types N or S mortar utilizing Portland cement, and sand that complies to ASTM(C)-144. The use of accelerators and/or acid washing is not recommended. Nine gauge ladder type reinforcing is to be used in horizontal joints with maximum spacing of 16 inches on center.

Glass block panels are to be framed and anchored at head and jamb locations with either a channel type restraint or with PC panel anchors that give the wall a much cleaner look. Panel anchors are spaced at no more than 16 inches on center up both jambs and across the head.

This information gives you a general idea of design considerations. However, to get more specific and accurate information for your specific project, contact us at Eastern Glass Block. We have over 20 years of experience in commercial and residential design and installation Glass Block projects. We would love to hear about your plans and share our expertise with you.


  1. […] a previous post about installing Glass Block, we covered height, load support, and anchoring guidelines for your project. In this post, we […]

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