Volume 37, Issue 9, September 2002
Easy as 1... 2... 3...
Guide to Ensuring Success on your Next Curtainwall Project
By John Juba
For varying curtainwall projects, glaziers can request back up systems for other façade materials such as granite or aluminum panels.
After 32 successful years in the glazing and curtainwall industry as a subcontractor, I have had the distinct privilege of working with some of the most successful architects, developers, general contractors and material suppliers in the construction industry. When I started my career with PPG Industries as a glazier, fabricator and curtainwall mechanic, I learned two very important principles still in effect today. They are, “a system only performs as well as its installation” and “the type of system selected for a project must be designed technically in a proper manner for that project.”
As a troubleshooter, consultant and systems designer, I have learned that one misplaced screw or weep hole or one bad detail can compromise an otherwise great system. I have learned a lot from my own mistakes and the mistakes of others; therefore my goal is to share some valuable information, which has contributed to many successful curtainwall projects.
The following is a guide to eliminating problems, which occur commonly in the curtainwall and glazing
Understanding Performance Requirements
It is important to know system performance requirements, and the difference between high- and low-performance systems. Basic performance criteria for high-performance systems have the following minimums:
• Air Infiltration: Not to exceed 0.06 CFM/sq. ft. of fixed area at 6.24 PSF.
• Water: Minimal differential pressure of 20 percent of inward acting wind load design pressure, but not less than 10 pounds PSF.
• Deflection: Normal-to-wall not exceeding L/175 of span up to 13 feet, 6 inches not exceeding L/240+1/4 inch for spans more than 13 feet, 6 inches. Parallel-to-wall not exceeding 75 percent of glass edge clearances; 1/8-inch maximum.
• Structural: One hundred percent of design load and 150 percent design for overload, maximum allowable deformation in framing L/1000 with no permanent damage to anchors or fasteners.
• Water Control: Collect water in the system and condensation in gutters and drain to exteriors through protected and baffled weep holes.
• Thermal: System shall have a CRF rating of not less than 55.
The following are also important steps toward eliminating curtainwall/ glazing problems:
• Understand and communicate basic glazing terminology;
• Recommend that the architect discusses glass performance criteria with mechanical engineers;
• Encourage architects/owners to consider system performance, tenant comfort, sun glare at interior and exterior effects to the surrounding area;
• Choose the proper sealants;
• Be cautious when providing assistance with detailing curtainwall systems;
• Submit system profile drawings and performance criteria with bid.
Left: This project in Concord, N.C., features a custom-designed stick-type and unitized curtainwall and panel-wall systems. Right: A glass and granite structural silicone curtainwall system was used for this Charlotte, N.C., project.
Working with Consultants
When working with a curtainwall consultant who is critiquing your proposed system, there are several points to keep in mind. First, communicate with the consultant and be a team player. Second, provide the consultant with a good understanding of your system’s design. Third, promote independent mock-up testing for structural, air and water performance for custom curtainwall systems.
Arm Yourself with Knowledge
As a contract glazier, it is important that you have a full understanding of construction tolerances for materials adjacent to the curtainwall system. For example, pre-cast erection and fabrication tolerances can affect the perimeter sealant joint size requirements severely. Additionally, concrete tolerances can affect the curtainwall horizontal sill installation severely.
It is also important to be aware of the effects of structural live loads on the proposed curtainwall design. For example, most stick-type curtainwall systems are designed for ¼-inch live load. If the live load is more than 5/16 inches to ½ inch of the curtainwall, the horizontal height must increase. If the live load is ½-inch or greater, a two-piece horizontal must be utilized.
It is also important to have a basic knowledge of design versus cost to minimize or avoid valued engineering alternates, therefore, providing a budget in the early design stages is helpful. Also remember that unitized curtainwall systems have a premium cost of approximately 25 percent over stick systems in the Southeast.
Glaziers may also encourage a curtainwall backup system for other façade materials such as granite, steel panels and aluminum panels. When doing so, promote a single-source responsibility of exterior façade. This reduces installation time, enhances continuity of air and water control and often reduces overall façade costs.
Lastly, always require a pre-glazing installation conference. This will reveal potential interface problems between curtainwall and adjacent materials. It is also important to include a visual mock-up on-site to review colors.
John Juba founded Juba Aluminum Products, based in Concord, N.C., in 1993, after working for more than 23 years in the glass and glazing industry.
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