Do it right the first time, save legal costs

By Ron Clawson
December 1, 2008

All major manufacturers of aluminum storefront systems, and all insulating glass fabricators and manufacturers provide written instructions for the proper installation of their products. Experience has shown me that many glass shops don’t know about those instructions or choose to disregard them.

The picture below shows a glass installation with problems. Can you spot them?

The little wood setting block is 1½ inches long and 1-inch wide. It is turned so only ¼ inch of the front lite of this insulating glass unit is supported, and it is 2 ½ inches from the vertical mullion. This unit is 10 square feet in size. All of the glass in this building was set the same way and on these little wood blocks, including IGUs up to 32 square feet.

The manufacturer of this insulating glass unit specifies: “Setting blocks must be located at the ¼ points of the insulating unit. Setting blocks must be at least as wide as the insulating unit, at least as high as the minimum edge clearance and 0.1 inch in length for each square foot of glass area with a minimum length of 4 inches.

Setting blocks must be made of a resilient material such as neoprene, santoprene, EPDM or extruded silicone. Setting blocks must be 80 to 90 Durometer, Shore A, in hardness, and meet the requirements of ASTM C864 Standard Specification for Dense Elastomeric Compression Seal Gaskets, Setting Blocks and Spacers.”

The biggest problem for this glazing subcontractor is the installation does not comply with the installation instructions from the glass fabricator or manufacturer, or referenced industry standards; therefore the 10-year warranty on the insulating glass is null and void. Without proper support the insulating glass unit will suffer premature seal failure and look like the picture below.

Moisture has entered the IGU airspace and damaged the unit. In this particular case most of the glass in this large building has failed due to improper selection and installation of the glass setting blocks.

There is no defense for this type of installation. When this gets to the courthouse, you lose, and depending on the size of the job, you might lose your business in the process. This problem could have been avoided by following the glass manufacturers’ installation instructions and the “Glazing Guidelines & Practices for Sealed Insulating Glass” available from NGA’s

The author is principal consultant of Glazing Consultants LLC, Henderson, Nev., 702/824-1083,