Curtain Wall Systems

What a Curtain Wall Is, and What It Is Not

A curtain wall is a non-structural building envelope. It carries its own weight and the wind load acting on it, and transfers both back to the floor slabs — but it carries no part of the building's structure. It hangs off the frame like a curtain, which is where the name comes from.

That distinguishes it from storefront, which is a similar-looking aluminium and glass assembly but is designed to sit between floors at grade level and span far shorter distances. Specifying storefront framing where curtain wall is required is a genuine and expensive mistake, and it happens.

Stick-Built or Unitised

Stick-built systems arrive as individual mullions, transoms and glass, and are assembled in place. Lower material cost, more forgiving of dimensional variation in the building, and it suits smaller projects and irregular geometry. The trade-off is site labour, weather exposure during installation, and quality that depends on workmanship in the air rather than in a factory.

Unitised systems are built as complete panels in a factory, delivered finished and glazed, and hung from the slab edge. Faster on site, far better quality control, and far less scaffold time — which on a tall building usually outweighs the higher unit price. Panels interlock at the joints with a split mullion, so one of the great advantages is that inter-storey movement is absorbed in the joint rather than fighting the frame.

The rough rule is that stick-built suits low-rise and complex shapes; unitised suits repetitive tall buildings where programme matters more than material cost.

How It Keeps Water Out

This is the part most often misunderstood, and it is worth explaining because it changes how a facade should be judged.

A properly designed curtain wall is not sealed against water on its outer face. It is a drained and pressure-equalised assembly. The outer line sheds most water; whatever gets past is collected in the glazing pocket and drained back out through weeps in the horizontals. The cavity behind the outer seal is deliberately vented so the air pressure inside it matches the pressure outside — because water is driven through a gap by a pressure difference, and if there is no difference, there is no driving force.

The practical consequence: a facade that relies on a continuous bead of sealant on its outer face to stay dry is badly designed. Sealant fails, and when it does there is no second line. Drainage paths must be kept clear during installation, and blocked weeps are a common cause of leaks on otherwise sound systems.

How It Is Tested

Curtain wall performance is not a claim, it is a test result. The relevant standards are ASTM E283 for air infiltration, ASTM E331 for water penetration under static pressure, and ASTM E330 for structural performance under uniform load. Dynamic water testing under AAMA procedures uses a propeller to simulate wind-driven rain rather than static pressure.

On significant projects the assembly is mock-up tested before production, and field testing to AAMA 502 or 503 checks the installed result. If a system is offered without test data behind the specific configuration, that is worth questioning.

The Details That Decide Whether It Works

Thermal break and condensation. Aluminium conducts readily, so the framing needs a polyamide or poured-and-debridged break separating inside from outside. Without it the interior mullion face runs cold and condenses in winter — on a large facade that is water running down the inside of the building. Condensation resistance is a separate rating from U-factor and worth asking about specifically.

Movement. Buildings move. Slabs deflect under live load, frames sway, and the facade expands and contracts through a temperature range far wider than the air temperature, as our waterproofing page explains. The system has to absorb inter-storey drift and thermal movement in designed joints, not by stressing the glass.

Anchors and slab edge. Every load ends up in the anchor. Tolerance at the slab edge is the single most common source of trouble on site, because concrete is not built to the tolerance aluminium is made to. Adjustable anchors exist for exactly this reason.

Perimeter fire barrier. The gap between the slab edge and the back of the facade is a route for fire and smoke between floors, and it requires a tested safing system. This is a life-safety item, it is inspected, and it is not a detail to improvise.

Spandrel zones. The areas covering floor slabs and ceiling voids are opaque but still part of the facade. They need shadow box or spandrel panel treatment, insulation, and careful attention to heat build-up behind the glass.

Glass selection. Large areas of glazing make solar control the dominant energy question, which is where Solarban 60 or 70 earns its place. Anything above ground level should be considered for laminated and heat-soaked construction.

Curtain Wall Across the Region

These describe the kind of work each area brings rather than any specific client project.

Long Island City and Downtown Brooklyn

Repetitive residential towers — the classic unitised case. Floor plates repeat, the programme is tight, and factory assembly plus fast hanging beats site labour comfortably. Wind pressure rises sharply with height, so the design pressure is the engineer's figure and drives glass thickness and anchor design.

Hudson Waterfront — Hoboken, Jersey City, Weehawken

The most demanding exposure in the region: high wind off open water, full eastern and southern sun, and salt. Pressure equalisation matters more here than almost anywhere, because wind-driven rain at pressure is exactly the condition a face-sealed facade fails under. Fixings and anchors want stainless of the correct grade.

Midtown and Hudson Yards

Commercial towers, frequently with structurally glazed or point-supported elements where the glass itself carries load at the fittings. Large panes, expensive to replace, difficult to access — which is the argument for 100 percent heat soaking and for documentation proving it was done.

Greenpoint, Williamsburg and the Brooklyn Waterfront

A mix of new towers and converted industrial buildings. Conversions are usually a stick-built or window-wall question, because the openings already exist and the structure is not built to a modern facade tolerance. New build on the waterfront is the same severe exposure as the Hudson side.

Low-Rise Commercial — East New York, Woodhaven, the Outer Boroughs

Smaller and more irregular projects where stick-built framing is the sensible answer and the energy code, rather than an architect's aesthetic, drives the glass specification. Often the honest advice is that the project needs storefront framing rather than curtain wall, and we will say so.

Getting Curtain Wall Quoted

Send us the elevations, the design pressure from the engineer and any performance specification you have been given. We quote against what the drawings require. If a system has been named we will price it; if not we will tell you what the building needs, including when a simpler assembly would do the job. We work across Manhattan, Brooklyn, Queens, the Bronx and Staten Island, and throughout Northern New Jersey, the Jersey Shore, Philadelphia and the Lehigh Valley.