Why Momentive says city data centers need sealant built for 1,000-foot towers

Waterline, a 74-story supertall tower in Austin, rises 1,025 feet and is the tallest building in Texas. UltraGlaze SSG4600 Structural Glazing Sealant, which provides 30 psi tensile design strength, was selected for its glass facade. Momentive, which makes that sealant, says the same high-load capability is now essential on a building that looks nothing like a luxury supertall: the urban data center.

The argument comes from Errol Bull, an application development leader at Momentive Performance Materials, in a piece glassonweb.com published on November 9, 2026. Building Enclosure ran a version of the article on October 28. Bull starts with location. He writes that proximity to end users and the demand for ultra-low latency have pushed infrastructure into city centers, with up to 97% of facilities now developed in or near metropolitan areas.

Cities change the brief. Expensive land forces developers to build up, and Bull says planning boards routinely turn down multi-story windowless concrete boxes in favor of glass-fronted designs that fit the streetscape. Swap concrete for ordinary windows, though, and the building risks weaker physical security, more solar heat gain, heavier HVAC loads and a worse Power Usage Effectiveness (PUE) rating. That leaves one practical question for the developer and the facilities lead who will run the site: what holds the glass, and what does that choice do to the server hall?

A glass coat around a concrete core

The glass doesn't go everywhere. In Bull's description, server halls stay heavily shielded from direct sun, while expansive glazing covers administrative offices, perimeter circulation zones and technical workstations. The people-facing parts of the building get daylight. The equipment stays in the dark.

In a conventional curtain wall, every pane is held in place by exterior pressure plates, bulky metal caps and exposed fasteners. According to Bull, those parts block sightlines, collect dirt and debris, and spoil the smooth, flush look that city planners favor. Structural silicone glazing (SSG) does away with the external retainers. The glass is bonded directly to an aluminum subframe, which leaves the exterior flush.

For a design team, that layout changes where the hard engineering sits. The glazed zones are mostly perimeter space, but they wrap the secure core, so the curtain wall has to meet a mission-critical building's standard for security and airtightness even where no servers sit behind it.

Heavy security glass on a thin bead

Glass is rigid. Building frames are not; they deflect under wind, shift with temperature and drift in seismic events. Mechanical fixings pin the glass at points and concentrate stress at its edges. A continuous elastomeric silicone bond spreads those loads along the whole joint and passes them into the subframe, working, as Bull puts it, as a built-in shock absorber.

High-load sealants were engineered for supertall towers facing high-altitude wind shear, severe thermal cycling and seismic drift. Momentive's Waterline case study shows the product class in use: UltraGlaze SSG4600, which provides 30 psi tensile design strength, high tear resistance and durable elasticity, was selected for the expansive glass facade of the 1.25-million-square-foot development designed by Kohn Pedersen Fox. Win-Con was the glazing contractor. Bull argues the same strength lets facade engineers specify much heavier multi-laminate security, acoustic and thermal glass on a data center while keeping joints narrow.

That weight is the part a security director will recognize. An October 5 guide from Impact Security, which makes the DefenseLite retrofit systems, calls glass the single weakest point in a data center's building envelope. UL 752 ballistic levels range from Level 1, 9mm handgun protection at roughly 1.2 inches thick, to Level 7, AR-15 rifle rounds at about 1.6 inches and 15 pounds per square foot.

Put the two sources together and the procurement link is plain, even though neither states it outright: the higher the security rating chosen for street-facing glass, the more the structural joint has to carry. A security spec and a sealant spec written by separate teams could easily end up with nobody checking that the two match.

Where the facade meets the cooling plant

Bull's second argument concerns humidity. A server hall's cooling and humidity strategy, he writes, is only as good as the enclosure around it. A continuous silicone seal limits air infiltration and thermal bridging through the glazed envelope, keeping unconditioned outside air and moisture out. That helps the HVAC system prevent condensation on hardware, lightens the load on the cooling plant and protects the tight relative humidity limits server halls run within.

When a city insists a data center look like an office building, the bead of silicone holding the glass ends up doing work for the cooling plant. Impact Security's guide makes a parallel point from the glass side: for data centers, even modest reductions in peak cooling demand translate directly into lower operating costs and improved power usage effectiveness.

Durability is the claim that matters over a building's life. Bull cites a 40-year outdoor weathering study measuring hardness, resilience, flexibility and adhesion, in which silicone sealants consistently outperformed acrylic and polyurethane alternatives and kept their structural integrity and flexibility without cracking or chalking. Neither version of his article identifies the study. For project teams, that suggests verification should come from their own testing rather than the trade article.

Moving the bonding indoors

Schedule is the third argument. Stick-built glazing is put together and sealed on site, which makes it slow and labor-heavy, and cold temperatures, rain and high humidity can all hold it up. Bull says fabricators can use fast-cure one- and two-part silicones with adjustable work patterns to bond and cure unitized panels inside a climate-controlled facility, then send the finished units out for installation. He writes that today's SSG sealants reach primerless adhesion rates as high as 96% on hard-to-bond substrates such as ceramic frits, fluoropolymer coatings and anodized aluminum. In the Building Enclosure version, Bull adds that assembling panels off site lowers on-site labor risk and reduces the need for extensive scaffolding.

For a developer racing to bring AI or cloud capacity online, removing the weather from the facade critical path is the most bankable part of the pitch. In Momentive's Waterline case study, primerless adhesion, rapid strength build-up and a flexible working time helped support Win-Con's installation across the tower's extensive facade system.

The case has a clear boundary. Impact Security notes that most U.S. data centers in operation are existing buildings where shutting down for a facade replacement isn't feasible, and those sites usually harden glass with shields mounted over existing panes. Bull's argument is for new multi-story urban builds. Facade choice also isn't the only route to coordinating the envelope: Saint-Gobain, for one, markets fire-rated glazing, panelized walls and insulation for data centers as a single integrated package meant to reduce handoffs between trades.

Three checks before the shop drawings

For an operator whose next site sits under a planning board that wants glass, a few questions are worth putting to the facade engineer and glazing contractor early:

1. What forced-entry or ballistic rating has security chosen for the street-facing glass, and has the structural joint been designed for that unit's weight?
2. Which glass coatings and frame finishes are on this project, and has adhesion been tested on those exact substrates? Momentive's own case study advises customers to rely on their own evaluation rather than reported results.
3. Where glazing forms part of a fire separation near server or electrical rooms, who owns the interface between the curtain wall and the fire-rated assembly?

The sealant line in a curtain wall package rarely crosses a mechanical engineer's or security director's desk. On a glass-fronted city data center, it touches both of their jobs, so it should get their review before the shop drawings are approved.