Guide

Aluminium window and door weather ratings explained

By Paul Fradley, Founder and Technical Lead · Updated June 2026

Aluminium windows and doors are weather-tested to three European standards: air permeability (EN 12207), watertightness (EN 12208) and wind resistance (EN 12210). Each returns a class. A higher class means the unit leaks less air, holds out more wind-driven rain and stays stiffer under wind load. On exposed sites those classes are the difference between a dry, draught-free opening and a callback, so specify the test class against your site exposure rather than trusting a single headline number.

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Aluminium window and door weather ratings explained, aluminium by VitrineAlu

Air permeability to Class 4Tested to EN 12207, to air permeability Class 4, the tightest band on the scale.

Watertightness to Class 9ATested to EN 12208, to watertightness Class 9A against wind-driven rain.

Wind resistance to Class C5Tested to EN 12210, to wind resistance to Class C5 for deflection and load.

What do the three weather ratings on aluminium windows and doors mean?

Every weather-tested aluminium window or door carries three separate classifications, each from its own European standard. They are measured together on a sample unit but reported separately, so read all three before you compare products.

Air permeability (EN 12207) measures how much air leaks through the unit under pressure. Watertightness (EN 12208) measures the pressure at which wind-driven rain pushes past the seals. Wind resistance (EN 12210) measures how the unit deflects and survives under wind load. A strong figure on one says nothing about the other two, which is why a like-for-like comparison needs all three classes confirmed for the whole unit at quote.

Air permeability: EN 12207, classes 1 to 4, where Class 4 is the tightest
Watertightness: EN 12208, classes up to 9A on the exposed scale, where higher resists more wind-driven rain
Wind resistance: EN 12210, a deflection letter A to C and a load band 1 to 5, where Class C5 is the stiffest and strongest combination

How does air permeability (EN 12207) work and why does it matter?

Air permeability is the draught and heat-loss test. The unit is pressure-cycled, the air leakage is measured, and the result is placed in a class from 1 to 4. Class 4 is the tightest band and the one to ask for on heated buildings. Our aluminium systems test to air permeability Class 4 where specified.

A tight air class protects comfort and running cost. Leaky junctions waste heat, undermine the thermal performance of the frame and let draughts track across a room near large openings. Pair a strong air class with the right whole-unit Uw for the building, and confirm both on the unit you are buying. See our energy efficiency page and the aluminium U-values guide for how the thermal numbers fit together.

Class 1: loosest, suited only to sheltered, unheated or low-spec uses
Class 4: tightest, the target for heated and exposed buildings
Pair with whole-unit Uw, confirmed at quote, for the real energy picture

How does watertightness (EN 12208) work and what does Class 9A mean?

Watertightness measures the point at which wind-driven rain beats the seals. Water is sprayed on the unit while air pressure is stepped up, and the class records the pressure held with no leakage. A higher class equals higher resistance to driving rain. Our systems test to watertightness Class 9A where specified, which is the top of the exposed-site scale.

The right water class follows site exposure. A sheltered urban infill has different needs to a coastal or hillside elevation that takes the full weather. Two scales appear in datasheets: the open-air A scale up to Class 9A, and the extended E scale for units that cannot be tested fully exposed. Read which scale is quoted, and confirm the figure for the whole unit, including any low threshold, at quote.

A scale, fully exposed: up to Class 9A, the open weather rating
E scale, extended: stated test pressures for partially sheltered conditions
Watch thresholds: low or level access can change the achievable water class, so confirm at quote

How does wind resistance (EN 12210) work and what does Class C5 mean?

Wind resistance has two parts: how far the unit deflects under a design wind load, and whether it survives a higher safety load without damage. The result is a letter for deflection, A, B or C with C the stiffest, and a number for load, 1 to 5 with 5 the highest. Class C5 is the top combination. Our systems test to wind resistance to Class C5 where specified.

Wind load rises fast with building height, exposure and openness of the surrounding ground. A large opening on an exposed elevation can see loads a sheltered site never reaches. A higher wind class means stiffer mullions and stronger fixings, which keeps seals working and glazing supported. On big spans the wind class and the unit size are linked, so size and class must be confirmed together at quote.

Deflection letter: A, B or C, where C is the stiffest under load
Load number: 1 to 5, where 5 carries the highest design and safety load
Class C5: the highest classed combination, for tall or fully exposed openings

How do the weather classes relate to security and curtain walling ratings?

The three weather tests are about wind and water, not forced entry, so they sit alongside security testing rather than replacing it. Security comes from separate routes such as PAS 24, including PAS 24:2025, plus cyclic durability to EN 12400 at up to 50,000 cycles on tested products. Acoustic performance to Rw 46 dB where specified is a fourth, separate rating again. Each answers a different question, so specify the ones your project needs. See security for the forced-entry detail.

Curtain walling is rated on its own standard, EN 13830, not EN 12207 to EN 12210. Its weather classes read differently: air to Class AE, watertightness to RE1200, and wind to an EN 13116 2000Pa design pressure where specified, with units to 1.5 x 3.6m at 350kg, a 66mm sightline and Ucw from 0.6, all confirmed at quote. If your project mixes windows, doors and screens, expect two rating families on the same job.

Weather: EN 12207, EN 12208 and EN 12210 for windows and doors
Security: PAS 24 routes including PAS 24:2025, durability to EN 12400 up to 50,000 cycles
Curtain walling: EN 13830, air Class AE, water RE1200, EN 13116 2000Pa design where specified

How do I specify weather ratings for an exposed site?

Start from site exposure, then set a minimum class for each of the three tests and state it on the order. As a working rule for an exposed elevation in the North West, aim high on all three: air permeability Class 4, watertightness toward Class 9A and wind resistance toward Class C5, then ask us to confirm what the chosen system achieves at the unit size you need.

Class is tied to size and configuration. A small fixed light reaches top classes easily; a 14-leaf bifold run or a large sliding sash works harder. Verified maxima to design around include bifold leaves to 1.2 x 3.0m at 130kg with up to 14 leaves and around 90% clear opening, and sliding sashes to 2.2 x 2.87m at 420kg. Give us the opening sizes and the exposure and we will quote the right system and confirm the whole-unit classes. Start at quote, browse products, or if you are a homeowner find a vetted fitter via find an installer.

State a minimum class for air, water and wind on the order
Match the class to the largest unit on that elevation, not the smallest
Confirm the whole-unit classes at quote before fabrication

Common questions

What is the highest weather rating for aluminium windows and doors?

The top classes are air permeability Class 4 (EN 12207), watertightness Class 9A (EN 12208) and wind resistance to Class C5 (EN 12210). Our aluminium systems test to these where specified, with the whole-unit class confirmed for your size and configuration at quote.

What does Class 9A watertightness mean?

Class 9A is the top of the exposed-site watertightness scale in EN 12208. The unit is sprayed with water while air pressure is stepped up, and Class 9A means it held the highest open-air test pressure with no leakage. It is the rating to target on coastal, hillside and other elevations that take wind-driven rain.

What does wind resistance Class C5 mean?

In EN 12210 the letter is deflection stiffness, A, B or C with C stiffest, and the number is load, 1 to 5 with 5 highest. Wind resistance to Class C5 is the top combination: the unit deflects least under design wind load and survives the highest safety load. It suits tall or fully exposed openings, and the class is confirmed against your unit size at quote.

Do weather ratings tell me how secure a window is?

No. EN 12207, EN 12208 and EN 12210 cover air, water and wind only. Security is a separate route, typically PAS 24 including PAS 24:2025, alongside cyclic durability to EN 12400 at up to 50,000 cycles on tested products. Specify both the weather classes and the security route your project needs.

How do I choose weather classes for an exposed site?

Set a minimum class for each of the three tests against your site exposure, aiming high on an exposed elevation: air permeability Class 4, watertightness toward Class 9A and wind resistance toward Class C5. Class depends on unit size, so match it to the largest opening on that elevation and confirm the whole-unit figures at quote.

Completed North West new build with VitrineAlu anthracite aluminium bifold doors, windows and dormers — The frame disappears, the view does the talking.

Proof, not promises

Specified and made by people who have fitted it

Paul Fradley, Founder and Technical Lead, has worked almost every role in windows and doors across more than twenty years: surveyed, fabricated on the floor, fitted on site, then ran the technical and operations side. He leads the spec on every project, so what we quote is what we fabricate.

4.5 / 5 from 20 Google reviews. Council for Aluminium in Building member. Tested to BS EN 14351-1 and BS EN 13830 where specified.

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