Behind the Curtain Wall: Maintaining a Critical Building Component

Nothing communicates modernity like a glass-walled building. Gleaming surfaces that mirror the sun and clouds – and seem to stretch as high – were once the stuff of science fiction, but today are ubiquitous. Why? Not simply because we strive to embrace the future. It’s because these gleaming building facades are so practical.

They keep the weather out and allow light to penetrate deep within. They give architects new opportunities for creative expression. And because they’re not tasked with preserving the building’s structural integrity, they can be made of lightweight materials, thus reducing construction costs. What’s more, they can be exceptionally long-lived.

These are all attributes of the curtain wall – so named because these shining surfaces hang – like a curtain – from the framework of the building. Their hallmark feature is that they’re non-structural. They don’t support a significant load; they’re not the skeleton that holds the building together. They’re more a building’s skin. And like our skin, a curtain wall can last for decades with proper care.

A window into the past

Glass curtain wall communicates modernity.

Throughout most of the history of building construction, exterior walls supported the load of the entire structure. But with the development and widespread use of structural steel and reinforced concrete, relatively small columns could support large loads, freeing exterior walls from the burden of supporting all that weight. Instead, glass or skins of metal, wood or other materials could be used as an exterior façade.

When we think of curtain walls and how to care for them, most of the time we’re talking about glass because of its widespread use. What’s changed is how glass today is incorporated into building design. Prior to the 1950s, most buildings featured windows that could be opened. Façade cleaning was relatively straight forward. Window washers strapped themselves into leather harnesses and hooked themselves to the sides of skyscraper windows. But when glass curtain walls became the building façade, windows didn’t open. Consequently, the cleaning crews required exterior access. To enable cleaning, buildings were constructed with flat roofs to accommodate fixed or mobile window-washing equipment. Mechanisms were developed to allow platforms to be suspended from rails or tracks on the roof, and they were moved up and down by the operator.

As technology progressed, buildings broke away from the flat-roofed silhouette. Slopes and recesses became common design features, and builders developed new forms of façade-access equipment, like arms that were used both for window washing and hoisting.

Façade access is essential not only for window washing, but also for metal cleaning, inspection of curtain wall conditions, and the hoisting of replacement panels. Straight-sided buildings primarily use rig mechanisms that are anchored to the roof for these purposes, but new solutions continue to be developed. Still, cleaning continues to be performed almost entirely by hand (although automated cleaning robots are being developed).

Now, a few definitions

In the world of building construction, you’ll hear about curtain walls, window walls and storefront glass. Here’s the difference: Curtain walls are not structural, or load bearing. They’re suspended over a building’s structural elements, and thus provide protection but not support.

Window walls have units of glass within the components of a structural, load-bearing wall. Storefront walls are only installed along the bottom floor, whereas curtain walls can be applied over any part of the building.

There’s another difference, too, which has to do with drainage. Storefront and window wall systems typically channel water across the horizontal and vertical perimeter of the installation. Curtain walls, however, are designed so that water drains from each unit individually. (The benefit of this is that water gets distributed across a wider surface, which reduces wear and tear.)

You may also have heard of unitized curtain walls and stick curtain walls. Aesthetically, they’re pretty similar. Unitized curtain walls, however, are assembled and glazed at the factory, then shipped for installation at the work site. Using anchors and mullions, installers fit them together horizontally and vertically. They’re usually installed sequentially by floor, from bottom to top. Stick curtain walls, on the other hand, are shipped in pieces, and are assembled, glazed and installed on site. They can be split and extended as needed, and can reach far greater heights than a unitized curtain wall (which can be extended to a maximum height of just two floors).

Maintenance of glass curtain walls and window systems

Curtain walls are easy to maintain, but it's important they do receive care.As we mentioned earlier, curtain walls can be very long-lived – half a century or more if properly maintained. And believe us, proper maintenance is essential. You’ll need to look at window gaskets or sealants for splits, breaks or openings, since these will be avenues for air and water to infiltrate. Dried, cracked, shrunken or otherwise damaged gaskets and sealants should be replaced ASAP. It’s also important to inspect surrounding exterior walls or mullions for rust, deformation and other signs of deterioration.

One thing we always look for is fogged or etched glass. It may not appear dramatic, but it can be a sign of condensation, itself evidence of a compromised thermal seal. And that means things will only get worse over time.

Preventive maintenance for anodized aluminum curtain walls

The other most common type of curtain wall is made from aluminum – a material that’s long lasting, strong but light, and easy to shape. Here again, establishing a program of preventive maintenance for your anodized aluminum curtain walls is the smartest thing you can do. You’ll protect future value, keep your operating budget in line, and avoid duplication of costs that comes with ad hoc maintenance efforts. Moreover, you’ll maintain your property’s curb appeal – boosting its prestige and enhancing tenant retention.

Regular preventive maintenance isn’t just cost-effective, it’s pretty fast and simple – especially compared to restoration and replacement resulting from a lack of maintenance.

Typically, maintenance of aluminum curtain walls will involve cleaning and the application of a clear protectant coat/sealer every 2-5 years. Restoration may be needed between 15 and 30 years. This would involve applying a high-performance architectural coating system and replacing façade weather seals. Afterward, the finish will look new, you’ll have an effective barrier against corrosion and water seepage. Sometime between 30 and 40 years, a major restoration or replacement may be necessary. Deferring maintenance can dramatically speed the timetable for major restoration and replacement, both of which are expensive and time-consuming undertakings.

Here’s what you need to remember about anodized aluminum curtain walls: Cleaning and scrubbing are ineffective against advanced surface corrosion. That’s because the original anodic protective layer isn’t terribly thick, and the raw aluminum beneath it has no natural corrosion resistance. As long as you clean and protect while the aluminum is in good shape, it will serve you well year after year. But after a certain point, there’s no return.

Prudence pays off

Many building managers and owners mistakenly believe that curtain walls are virtually maintenance free. The fact is, they’re long-lasting ONLY if they’re maintained. And that requires good planning and responsible investment.

What do we mean by “responsible investment?” The bottom line is: Don’t take shortcuts.  Choose a maintenance provider that has a proven record of success; that comes with good references; and will take the time to answer all your questions so that you can make an informed decision. The safety and value of your building depends on steady, expert care. And believe us, the price you pay to maintain your building is nothing compared what you’ll pay to fix it.

Talk to us about your concerns. We’ll come right out, walk the property with you, and develop a plan at no charge. Believe us, we’ve seen it all – and we can do it all.


HSG is compliant with all CDC, OSHA, State Guidelines and Applicable Laws of Covid-19. HSG Employees have been trained, and provided the necessary PPE tools to ensure the safety of all.  It is a top priority of HSG to maintain a safe work environment at all times and throughout the current crisis.