What are the inspection items for glass curtain walls?

Glass curtain walls are common “outerwear” for modern high-rise buildings. They are beautiful and light-transmitting, but various problems may occur after about 10 years of use, such as water leakage, glass cracking, metal rust, etc. In order to ensure the safety and reliability of glass curtain walls, professional inspections are required regularly. The following are common glass curtain wall inspection items, which are divided into several large blocks for specific explanation:

1. Material inspection: glass, metal, glue
Just like checking the quality of bricks and cement when building a house, the inspection of glass curtain walls must first check whether the materials are qualified.

1. Whether the glass itself meets the standards
Strength test: Tempered glass must be hard enough to withstand impact. During the inspection, instruments will be used to press the surface of the glass to see if it can reach the specified strength.
Is the laminated glass firmly adhered: There is a layer of adhesive film (such as PVB glue) in the middle of the laminated glass. During the inspection, try to tear the glass layer apart to see if the adhesive film will fall off. If it separates as soon as it is torn, it means that there is a problem with the quality.
Is there any air leakage in the insulating glass: Insulating glass is two layers of glass with dry air or inert gas in between. During the inspection, the glass will be placed in a low temperature environment (such as minus 40℃). If fog and condensation occur in the middle, it means that the seal has failed and air has leaked in.

2. Metal frames and accessories
Aluminum profile hardness and thickness: The aluminum alloy used for the frame cannot be too soft. During the inspection, a tool similar to “fingernail scratching” will be used to measure the hardness, and a caliper will be used to measure the thickness to ensure compliance with the standard.
Is the surface coating durable: Metal frames usually have fluorocarbon coatings to prevent rust. During the inspection, the coating thickness is measured by instruments (for example, at least 30 microns, equivalent to half the thickness of a hair), and chemical reagents are used to test whether the coating is easy to fall off.

3. Is the glass curtain wall glue aging
The glass and metal are sealed with glue, and the glue may harden and crack over time. During the inspection, the glue strip will be pressed by hand to feel the hardness (for example, the hardness of normal silicone is similar to that of an eraser), and a small piece of glue will be cut off for a tensile test to see how much force it can withstand before breaking.

2. Structural safety: wind resistance, earthquake resistance, and anti-falling
The glass curtain wall is hung at a height of dozens of meters. It is most afraid of strong winds, earthquakes, or sudden glass falling. Therefore, it is necessary to check whether its “bones” are strong.

1. Wind resistance test
Simulate strong wind weather, use a large fan to blow at the curtain wall, and use sensors to measure the deformation of the glass and frame. For example, in typhoon-prone areas, the curtain wall is required to withstand wind force above level 12 (equivalent to a pressure of 600 kilograms per square meter). If the glass is blown and shakes obviously or the frame squeaks, it means there is a problem.

2. Earthquake resistance
In the laboratory, the curtain wall model is installed on a vibration table to simulate the shaking during an earthquake. Test whether the curtain wall can withstand the swaying of the building without cracking, especially whether the metal parts connecting the glass and the frame will break.

3. Prevent glass from falling
Check whether the metal fasteners that fix the glass are rusted or loose, such as using a wrench to tighten the screws to see if they are threaded, or use a tensile machine to test the load-bearing capacity of the fasteners (for example, it must be able to pull at least 2 tons of weight). If it is a hidden frame curtain wall (the frame cannot be seen from the glass exterior), check whether the structural glue is aged and ineffective.

3. Waterproof and leakproof: Will it seep in on rainy days?
Water leakage in glass curtain walls is a common problem, especially at the joints. During the inspection, a rainstorm environment will be simulated, and three places will be checked in particular:

1. Overall water spray test
Use a high-pressure water gun to spray water on the glass curtain wall (the amount of water is about 3 liters per square meter per minute, equivalent to a heavy rainstorm) for more than 15 minutes. People in the room observe whether there is water seeping in from the joints, or water droplets appear on the inside of the glass.

2. Glue joints and drainage holes
Check whether the glue has cracks or bubbles, especially in places where the sun is directly exposed (the glue is easily aged by ultraviolet rays). In addition, check whether the drainage holes on the metal frame are blocked by dust, causing rainwater to accumulate in the frame and not be drained out.

3. Windows and opening sashes
If the curtain wall has openable windows, open and close them repeatedly to test whether the sealing strip is deformed and whether there is air leakage or water leakage after closing. Some inspections will use a smoke pen to spray smoke outside the window to see if the smoke will get into the room through the gap.

4. Energy-saving performance: keep warm in winter and heat insulation in summer
If the glass curtain wall has poor heat insulation, it will make the room become a “steamer” in summer and the heating will leak out in winter, wasting energy. The inspection mainly looks at two points:

1. Heat insulation ability
Use professional instruments to measure the heat transfer coefficient (U value) of the glass. The U value of ordinary single-layer glass is about 5.0, while the U value of good hollow LowE glass can be less than 1.5, and the insulation effect is increased by more than 3 times.

2. Sunshade effect
Check whether the glass reflects too much sunlight (such as some coated glass) or whether it is easy to let heat enter the room (solar heat gain coefficient SHGC). For example, in the south, glass with a low SHGC value is more suitable and can reduce the power consumption of air conditioners.

5. Fire and lightning protection: The bottom line of safety cannot be broken
High-rise buildings are most afraid of fire and lightning strikes, and glass curtain walls must be well protected:

1. Fire isolation zone
There must be fire blocking between the upper and lower floors of the curtain wall (such as filling the gap with rock wool) to prevent the flames from running upstairs along the curtain wall in case of fire. During the inspection, the local blocking material will be cut to check whether it is filled and resistant to high temperature.

2. Lightning protection system
The metal frame of the curtain wall must be connected to the building lightning protection network. During the inspection, the resistance value of the connection point is measured with a resistor (required to be less than 0.03 ohms) to ensure that the current can be smoothly introduced into the ground when lightning strikes, rather than discharged through the glass.

6. Daily inspection: problems that can be seen by the naked eye
In addition to professional instrument inspection, the following details should also be paid attention to during daily maintenance:

Glass surface: whether there are cracks, scratches, bubbles (especially the edges, which are fragile under stress).
Metal frame: whether it is rusty, paint-shedding, or deformed (for example, it is knocked crooked by the air conditioner outdoor unit).
Glue joint: whether it is moldy, yellowed, or degummed (you can use a hard card to scratch it lightly to see if it is powdered).
Abnormal sound: whether there is a creaking sound on a windy day, which may be caused by loose screws or friction of rubber strips.

The inspection of glass curtain walls seems complicated, but each item is related to safety. For example, in 2018, an accident occurred in a certain city where the curtain wall glass fell off and injured pedestrians. Afterwards, it was found that it was caused by aging glue. Regular inspections can not only avoid danger, but also extend the life of the curtain wall and reduce maintenance costs. If ordinary owners find that the curtain wall has abnormalities, such as water leakage, abnormal noise or glass cracks, they must contact professional institutions for inspection in time, and never handle it by themselves!

I hope that after reading this article, everyone will know the necessity of glass curtain wall inspection. If your glass curtain wall has been around for more than ten years, do you have a moment to think about whether your glass curtain wall is still healthy?