Why Three Numbers Matter More Than a Brochure
When a curtain wall package is tendered, most of the conversation is about appearance: mullion width, glass colour, panel joint rhythm. The specification that actually decides whether the facade will still be watertight after a decade of typhoons is a short line of grade numbers — air tightness, water tightness and wind load resistance. In China these grades are not marketing labels; they come from a fixed test and classification system, and they can be verified on a test rig before a single panel is fabricated.
Guangdong Rodoer Construction Co., Ltd. has been building curtain wall, door and window systems since 2008, holds Grade 1 professional contracting qualification for building curtain wall works and Class A qualification for curtain wall design, and supplies facades for landmark, commercial, public and high-end residential projects. The company's standard curtain wall systems are engineered to wind pressure resistance Class 9, water tightness Class 6 and air tightness Class 8 — and every one of those figures is a specification decision, not a slogan.
The Three Core Grades and What They Measure
Each grade answers a different physical question, and they are tested separately.
| Grade | Physical question | Test condition | Rodoer standard |
|---|---|---|---|
| Wind load resistance | Does the frame and panel deform or fail under positive and negative pressure? | Statistically calculated design wind pressure applied to a full-size mock-up; deflection and residual deformation measured | Class 9 |
| Water tightness | Does water penetrate the inner face under simultaneous wind and rain? | Fixed and fluctuating pressure with simultaneous water spray at the outer face | Class 6 |
| Air tightness | How much air leaks through the closed assembly per unit area? | Pressure difference step test on a sealed mock-up | Class 8 |
A facade can look identical in two projects and differ by three or four grades. The grade is a result of profile wall thickness, joint design, gasket count and drainage geometry — all of which are manufacturing decisions.
Wind Load: Where the Grade Requirement Comes From
Wind load resistance is the only one of the three that cannot be chosen freely. It is derived from the project itself. The design wind pressure is calculated from the basic wind pressure of the site, the terrain roughness of the surrounding area, the height variation coefficient and the shape coefficient of the facade, and the result determines the class the system must reach.
The practical consequences are significant:
- Coastal and typhoon-prone regions (Guangdong, Fujian, Hainan, and comparable overseas markets) carry high basic wind pressure, and corner zones of a tower can experience local suction far above the average facade value.
- Height amplifies everything. The same system on a 30 m building and a 200 m tower is not the same engineering problem; grade requirements rise with height, not linearly.
- Deflection limits still apply. A system can resist the pressure without failing and still be rejected, because excessive mullion deflection cracks glass and opens joints. Our systems keep deflection within the limits required for the glass and panel assemblies used.
This is why we ask for the project location, building height and facade zones before quoting a system. A Class 9 answer for a low-rise inland project is over-engineering; a Class 6 answer for a Pearl River Delta tower is a risk.
Water Tightness: Class 6 and the Details Behind It
Water tightness is the grade that generates the most after-sales complaints and the one most often lost in execution rather than design. Class 6 means the system has been verified against a defined combination of pressure and water spray without water reaching the inner face.
Reaching it consistently depends on three design habits that Rodoer applies across its curtain wall and window systems:
- An equal-pressure chamber behind the outer joint. The cavity is deliberately vented so that the air pressure behind the rain screen approaches the external pressure, which removes the driving force that pushes water inward.
- Multi-layer EPDM sealing with a separated drainage path. Water that passes the first gasket is routed down and out through a dedicated drainage channel instead of accumulating against the inner seal.
- Hidden structure and controlled joint geometry. In our modular concave-convex curtain wall and hidden-frame systems, the structural connection sits behind the weather seal, so the seal is not interrupted by exposed fixings.
Air Tightness, Thermal Performance and Energy Use
Air tightness Class 8 sounds like a comfort specification; in practice it is an energy and condensation specification. Every cubic metre of air that leaks through a facade carries heat with it, and in a sealed, air-conditioned commercial building the annual cooling load penalty of a poorly sealed facade is measurable.
Air leakage also moves moisture. In humid coastal climates, warm moist air driven through the facade into a cooler cavity is how condensation, mould and corrosion of fixings begin. Our curtain wall systems target air tightness Class 8 and thermal transmittance U ≤ 1.8 W/(m²·K) as a matched pair, because improving one without the other simply relocates the problem.
The Grades Buyers Frequently Forget to Specify
Wind, water and air get the attention. Four more performance requirements decide whether the facade works as an engineering system:
- Thermal transmittance (U value) — set by the energy code of the destination market, and strongly influenced by the thermal break width and glass build-up.
- Acoustic insulation — critical for facades facing roads, rail and airports; the required rating depends on the external noise spectrum, not on a single dB number.
- Fire performance — fire-resistant infill and fire-rated window and door elements, with certified ratings, are increasingly a project requirement rather than an option.
- Seismic and inter-storey drift capacity — the facade must accommodate frame movement without losing its weather seal, which is a connection design issue.
How Performance Is Confirmed Before Delivery
Performance grades should be evidenced, not asserted. For project packages, Rodoer supports the following chain of verification:
| Stage | What is confirmed |
|---|---|
| Design review | Wind load calculation, grade targets, thermal and acoustic targets per facade zone |
| Shop drawing and structural check | Mullion and transom section sizing, deflection control, connection and anchor design |
| Mock-up testing | Air, water and wind performance of the actual system, tested as a full-size assembly |
| Production and inspection | Profile thickness, gasket specification, sealant and drainage geometry checked against the tested assembly |
| Site and handover | Installation tolerances, drainage continuity, and after-sales service |
Our qualification base includes Grade 1 contracting for building curtain wall works, Grade 1 for metal door and window works, and Class A design qualification, together with China Green Building Materials Product Certification as a Specialized and Innovative Enterprise. In 2023 the company was one of only two curtain wall companies recognised as an A-Level Supplier by CSCEC Steel Structure South China Region.
Specify the Project, Not the Catalogue
Grades only have meaning against a specific building: its location, height, orientation and use. Send us the project city, building height, facade area and the performance targets from your specification, and our engineering team will respond with the system family, the achievable grade combination and the profile and glass configuration that support it.