How to Choose the Right Framed Curtain Wall System for Your Building

If you’ve ever looked up at a modern glass-clad office tower or a sleek commercial building and wondered what holds all that glass together, the answer is a curtain wall system. It’s one of the most important decisions a building owner, architect, or contractor will make, and getting it right can mean the difference between a building that performs beautifully for decades and one that causes headaches from day one.

In this guide, we’ll walk you through everything you need to know about choosing the right framed curtain wall system for your project, from understanding the basics to evaluating materials, performance specs, and installation requirements.

What Is a Curtain Wall and Why Does It Matter?

A curtain wall is a non-structural outer covering of a building. Unlike traditional load-bearing walls, it carries no floor or roof loads. Its job is to keep the weather out while letting light in, and to give the building its exterior appearance. Because it’s suspended from the building’s structural frame, it gives architects enormous design freedom.

For commercial buildings, high-rises, hospitals, airports, and schools, a well-designed curtain wall system is essential. It affects energy efficiency, acoustic performance, waterproofing, fire resistance, and of course, aesthetics. Choosing the wrong system, or the wrong supplier, can lead to water infiltration, thermal bridging, structural movement issues, and costly repairs.

At Starveil Windows, we work with architects and contractors to help them find the right system for each unique project. Here’s what we’ve learned about making that choice well.

Knowing the Types of Framed Curtain Wall Systems

Stick-built systems are assembled on-site, piece by piece. The mullions (vertical members) and transoms (horizontal members) are installed first, and then the glass or infill panels are dropped in. This system offers flexibility for complex geometries but is more labor-intensive.

Unitized systems are pre-assembled in a factory as large panels and then lifted into place on the building. They’re faster to install and offer better quality control, making them ideal for high-rise projects with repetitive floor plates.

There’s also a distinction between pressure-equalized and face-sealed systems. Most modern high-performance framed curtain wall systems use pressure equalization, which manages water infiltration through air pressure balancing rather than relying solely on sealants.

Why Aluminum Is the Dominant Material Choice

When it comes to framing, the aluminum curtain wall system has become the industry standard for good reason. Aluminum is lightweight, strong, corrosion-resistant, and highly workable, meaning it can be extruded into complex profiles that accommodate glazing, drainage channels, and thermal breaks all in one piece.

Here’s a quick comparison of common framing materials:

For most commercial projects, an aluminum curtain wall system with a thermal break is the go-to choice. The thermal break, usually a polyamide strip inserted between the interior and exterior aluminum sections, dramatically reduces heat transfer and helps the system meet energy codes.

If you’re working on a project with very high energy performance requirements or unusual environmental conditions, fiberglass-reinforced systems are worth evaluating, though they come at a premium.

Key Performance Criteria to Evaluate

Once you’ve decided on framing material, the selection process gets more technical. Here are the performance criteria that matter most:

Structural Performance

Your system needs to handle wind loads specific to your location. A building on the Gulf Coast of Pakistan or in a high-wind coastal zone needs a system rated for significantly higher pressures than one in a sheltered inland location. Check the system’s tested pressure ratings and confirm they exceed your local code requirements.

Water Resistance

Water infiltration is the most common failure mode in curtain wall systems. Look for systems with tested water penetration resistance (ASTM E331 or equivalent) and verify the drainage design. A good framed curtain wall system has a continuous drainage plane and weep holes to safely direct any incidental water to the exterior.

Thermal Performance

U-value (or U-factor) tells you how much heat the system conducts. The lower the number, the better the insulation. For most commercial projects in moderate to hot climates, aim for a center-of-glass U-value below 1.8 W/m²K. Solar Heat Gain Coefficient (SHGC) is equally important in sunny climates, as it affects cooling loads significantly.

Air Infiltration

Air leakage drives both energy loss and occupant discomfort. Systems should be tested to ASTM E283 or equivalent, and your specification should set a maximum allowable air infiltration rate.

Acoustic Performance

For buildings near airports, highways, or in dense urban areas, Sound Transmission Class (STC) ratings matter. A standard aluminum curtain wall system with single-pane glass won’t cut it here. You’ll need laminated glass or insulated glazing units (IGUs) with specific interlayer configurations. Pairing your curtain wall with high-performance aluminium windows at operable vents within the facade can further improve acoustic and thermal results.

The Curtain Wall Installation Process: What to Expect

Understanding the curtain wall installation process helps you plan timelines, coordinate trades, and avoid surprises.

Here’s a general overview of how it typically goes:

1. Anchor Installation

Steel or aluminum anchor plates are embedded in or bolted to the building’s concrete or steel structure at each floor slab. These are the connection points for the curtain wall frame and must be set with high precision.

2. Mullion Erection

For stick-built systems, vertical mullions are connected to the anchors first. They’re typically two floors tall and splice together to accommodate structural movement. For unitized systems, the stack joints and interlock mullions between panels serve the same structural role.

3. Transom and Infill Installation

Horizontal transoms are installed between the mullions, and then the glazing or other infill panels (spandrel panels, metal panels, stone) are set into the framing and secured with pressure plates and caps. On projects where roof sections meet the curtain wall, a skylight system is often integrated at this stage to carry natural light deep into the building interior.

4. Sealing and Weatherproofing

Silicone sealants and EPDM gaskets are applied at joints and transitions. This is critical work and should only be done by trained applicators. Improper sealing is one of the most common causes of early system failure.

5. Testing and Commissioning

Before the scaffolding comes down, the installed system should be tested for air and water infiltration. Field testing per ASTM E1105 is common on larger projects and gives you documented evidence that the installation meets the specification.

The curtain wall installation process timeline varies considerably by project size. A typical mid-rise building floor might take two to four weeks per floor for a stick system, while a unitized system on the same floor could be installed in a few days once panels arrive.

Common Mistakes to Avoid

Even experienced project teams run into trouble with curtain wall selection and installation. Here are the pitfalls we see most often:

Choosing based on price alone is the biggest mistake. A system that saves money upfront but leaks or requires frequent maintenance will cost far more over its lifecycle. Always evaluate total cost of ownership.

Underspecifying for local conditions is another common error. Wind loads, seismic requirements, and thermal performance targets vary by location. Make sure your system is specified and tested for your actual site conditions, not just average conditions.

Skipping field testing means you won’t know if the installation meets spec until water shows up inside the building. Budget for field testing during construction.

Not coordinating with other trades early enough causes problems with anchor placement, perimeter fire safing, and transitions to roofing and flashing systems. Bring the curtain wall contractor into coordination meetings early.

Questions to Ask Your Curtain Wall Supplier

Before you commit to a system, here’s what to ask:

• What test reports do you have for this system, and at what pressure ratings?
• Is the system available with a thermally broken frame?
• What glazing options are compatible with this system?
• Do you provide technical support during the curtain wall installation process?
• What are the lead times for your standard and custom extrusion profiles?
• Do you offer a product warranty and a weathertightness warranty?

At Starveil Windows, our team is happy to walk you through these questions for any project you’re evaluating. Getting the right answers early saves time and money downstream.

Frequently Asked Questions (FAQs)

What is the difference between a curtain wall and a storefront system?

A curtain wall spans multiple floors and is designed to handle significant wind loads and structural movement. A storefront system is a lower-cost framing system designed for ground-level applications with smaller spans and lower performance requirements. They look similar but are engineered very differently.

How long does a curtain wall system last?

A well-designed and properly installed aluminum curtain wall system can last 40 to 60 years or more. The glass sealants and gaskets may need replacement after 20 to 30 years, and the glazing itself may be upgraded for energy performance before the frame needs replacement.

What is a thermal break and why does it matter?

A thermal break is an insulating material (typically polyamide) inserted between the interior and exterior sections of an aluminum frame. Without it, the aluminum acts as a thermal conductor, transferring heat directly through the wall. A thermally broken framed curtain wall system significantly reduces heat loss and prevents condensation on interior frame surfaces.

Can a curtain wall system be used on a low-rise building?

Yes. While curtain wall systems are most commonly associated with high-rise construction, they are used on buildings of all heights. For low-rise projects, stick-built systems are often the most economical choice.

What permits are typically required for curtain wall installation?

This varies by jurisdiction, but most commercial projects require building permits, engineer-stamped shop drawings, and in some cases, special inspection of the anchor installations. Your contractor and local authority having jurisdiction (AHJ) will define what’s required for your specific project.

How do I know if an aluminum curtain wall system meets energy code?

Ask your supplier for whole-system performance data, including U-value and SHGC for the combined frame and glazing assembly. These numbers should be compared against the requirements in your applicable energy code (such as ASHRAE 90.1 or local equivalents). Performance modeling software can help confirm compliance for your specific orientation and climate zone.

Final Thoughts

Choosing the right curtain wall system is a process that rewards careful research, good specification writing, and early collaboration between architects, engineers, and contractors. The framed curtain wall system you select will define the building’s appearance, comfort, and energy performance for decades.

Whether you’re evaluating an aluminum curtain wall system for a new high-rise or planning a retrofit on an existing building, getting the technical details right from the start is what separates a successful project from a costly one. The curtain wall installation process is complex but manageable when everyone understands the requirements and the system is well suited to the job.

If you’d like to discuss your project and explore your options, reach out to the team at Starveil Windows. We’re here to help you make the right call.