“Why should I get an independent agency to conduct on site tests on a tested façade or window when it has already been tested at a lab and certified?”
A curtain wall façade, aluminium window or door is made up of several components which are cut, fabricated and assembled at a factory before it is installed at the project site. The manufacturers of each component which forms a part of the window would have issued test certificates for their specific product quality but how the component as a part of a system will perform remains untested.
Why test if I am using a pre tested system?
If the developer chooses to use a window or door system from a system supplier which has already been tested for certain specifications then the test certificates for tests conducted in their in house lab or in the country of origin are submitted as proof of performance. However the window fabricated by the system supplier in the country of origin and the quality of the same window fabricated by the approved franchisee in India may not be the same. Under these circumstances it becomes necessary to put in a clause in the tender that the windows will be tested by a third party independent laboratory on a progressive basis. Generally a sample size of 2.5% of the number of windows is considered a representative sample for testing by international consultants.
What if do not have a budget for off site testing?
Another scenario where on-site testing would be opted for is when the size and the number of windows used in a particular project may not
justify the costs for an offsite testing or there is no budget available. Under these circumstances a few onsite tests are the only option left to reassure the developer that there has been no dilution in the performance of the system he has chosen while it is fabricated by a franchisee of the system supplier. The structural performance of the system may not vary widely as the alloy and temper of the aluminum used would almost be the same irrespective of where the profile is extruded. However the performance of the window with regard to air infiltration and water penetration is entirely dependent on the fabrication skill of the window fabricator.
How can I ensure consistency in the quality of the window supplied and installed?
An onsite testing is also a process specified by the developer to ensure every window delivered to his site matches the performance specified by the consultant and is installed with due care. As the windows installation begins in the project an onsite test is conducted by a third party agency on a random window identified by the developer on a progressive basis. If there are any failures identified during the test then the cause of failure is analyzed and corrective action is done on all the windows installed and adequate care is taken by the contractor during fabrication to prevent such mistakes.
On site testing for windows and doors is conducted as per ASTM E 1105 or AAMA 502.02. Both these specifications recommend an air and water test using two methods. The most common method used is to construct a small temporary chamber using aluminium frames and 6 mm plywood to enclose the window from the inside of the building. This chamber is made air tight. An array of nozzles is installed 400 mm(see diagram 1) from the outside surface of the window. Water is sprayed at a flow rate of 3.4 lts/minute/ sq mt on the window at 30-35 psi. A negative pressure is created inside the chamber using a blower and the inside of the window in inspected for water ingress after 15 minutes of spraying. The same blower is also used to suck air out of the chamber through an air flow meter connected in the pipeline to measure the air infiltration.
For onsite testing of curtain walls, skylight and shop fronts AAMA 501.2 are the recommended method. This method involves spraying water on the vertical and the horizontal grooves of the curtain wall system using a specially designed calibrated nozzle at 30-35 psi pressure. The nozzle is held 305 mm from the exterior surface of the curtain wall and gently moved on the groove line for 5 minutes to cover 1.5 mts length. Thus it may take around 25 to 30 minutes to cover all the groove lines within the identified sample area.
A third party agency specialized in on site testing would be able to conduct the test without any bias and submit a detailed report on the results of the test with photographs after submitting a clear method statement of the process followed . The results of the test can be analyzed by the façade consultant and the root cause of failure ,if any, is identified and thereafter corrective can be action taken to prevent further such failures during the execution of the rest of the project.
For the building owner such on-site tests ensure that the windows or curtain walls they have used in their project performs to its full efficiency without any dilution in quality of fabrication or installation.