Door and window performance testing: EN 14351 and CE

A window is a test result before it is a product

Picture a facade package out to tender. Two suppliers quote for the same run of windows. One hands over a Declaration of Performance that states a watertightness class, a wind load class, an air permeability class and a thermal value for the exact configuration shown on the drawings. The other sends a polished brochure and the assurance that the units are "CE compliant". On a rain-lashed, wind-exposed elevation, only the first supplier has actually shown what the window will do once it is installed. Closing that gap is the whole job of EN 14351 and the testing behind it.

For windows and external pedestrian doorsets sold into the European market, performance is not a sales claim. It is measured on a test rig, graded against a published scale and then declared. The product standard EN 14351-1 is harmonised under the Construction Products Regulation, so a manufacturer placing these units on the market prepares a Declaration of Performance and applies the CE marking on the strength of genuine test data. Internal pedestrian doorsets fall under EN 14351-2, which is a product standard but is not harmonised, so those units take a different path and are not CE marked under the same construction-products regime. Working out which part of the standard your product sits under is the first decision a fabricator makes, and it shapes everything downstream. Eurocert handles that scoping as part of EN 14351 testing and CE marking for doors and windows, before a single unit is built.

The characteristics that actually get tested

The core of the standard is a defined set of essential characteristics. A laboratory never tests a window in the abstract. It tests one specific configuration, meaning a particular frame material, size, glazing build-up, hardware and opening type, and the result belongs to that configuration alone. Three of these characteristics decide whether a window survives real weather.

Air permeability is measured by sealing the unit into a chamber and stepping the air pressure up and down while leakage is recorded (test method EN 1026, classification EN 12207). The result places the window in a class from 1 to 4, where the higher class leaks least. This is the figure that quietly governs heating bills and draught complaints once people move in.

Watertightness subjects the closed unit to a controlled spray while pressure is raised in stages (EN 1027, classified to EN 12208). The class records the pressure at which water first forces its way to the inside face. A window destined for an exposed coastal tower needs a far higher class than one set deep under a balcony, and specifying too low a class is a frequent cause of site callbacks.

Resistance to wind load loads the window with positive and negative pressure to reproduce gusts pressing on and dragging at the facade (EN 12211, classified to EN 12210). The grading captures both the pressure the unit withstands and how far the frame deflects, because a sash that bows under load will in time break its own seals and lose its water and air ratings with it.

Around this weather trio sit the characteristics that specifiers now read first. Thermal transmittance, the Uw value in watts per square metre kelvin, is the headline energy number, where a lower value means less heat lost; it is established either by hot-box measurement or by calculation to EN ISO 10077. Acoustic performance, the weighted sound reduction index Rw in decibels, carries real weight on roadside and city-centre buildings. Safety in use covers behaviour under human impact (EN 13049) and the load-bearing capacity of the devices that restrain an opening sash. Operating forces, durability across thousands of opening and closing cycles, and resistance to forced entry complete the menu a specifier can ask a manufacturer to put on record.

From the test bench to the Declaration of Performance

Test data only earns its keep once it is locked down as the product type. The standard does this through Initial Type Testing: the configuration is tested for each characteristic the manufacturer intends to declare, and those results define the type. For windows and external pedestrian doorsets the assessment generally runs under System 3, in which a notified testing laboratory performs that initial type testing and issues the report the manufacturer then relies on.

This does not mean retesting every characteristic from zero for every product. Results can travel down a supply chain, so a fabricator building to a system house's verified design can often carry that system house's type-test results across to its own units, on the condition that it builds them exactly as tested. Thermal performance can be established by calculation or by tabulated values rather than a physical hot box. Each characteristic a manufacturer chooses not to assess is declared as "No Performance Determined", but that NPD entry is only safe where the destination market places no requirement on the characteristic. Declare NPD for watertightness on a rain-exposed elevation and a specifier is fully within rights to reject the unit.

Initial type testing is only half of the obligation. The standard also calls for factory production control, the manufacturer's own routine of checks that keeps day-to-day production matching the unit that passed on the rig. A type test proves the design can perform; factory production control is what gives a buyer confidence that the thousandth window off the line behaves like the one the laboratory saw. Treating that ongoing control as paperwork rather than a real discipline is how good test results slowly stop describing what actually ships.

The Declaration of Performance gathers these declared values against the product, and the CE marking points straight back to it. When an architect or a building-control officer reads the DoP, every class and value on the page traces to a test on a rig or a calculation that a laboratory stands behind. That traceability is what turns "CE compliant" from a slogan into something a buyer can check line by line.

Where door and window testing trips manufacturers up

The costly mistakes tend to happen after the laboratory work, not during it. A type test belongs to the configuration that was tested. Swap the hardware, change the reinforcement, widen the sash past the tested range or substitute a different glazing unit, and the original result may no longer hold. Fabricators who treat a single test report as a blanket pass for a whole catalogue are the ones who get caught when a client's technical reviewer asks for the test evidence behind a specific size.

Internal doorsets cause a recurring misunderstanding. Because EN 14351-2 is not harmonised, an internal pedestrian doorset is not CE marked through the construction-products route, yet it can still be performance tested for acoustic rating, durability or fire and smoke behaviour when a project calls for it. Fire and smoke characteristics in particular are tested and classified under their own standards, and they often dominate the specification for corridors and escape routes. A door can be entirely legitimate and well documented without a CE mark, as long as everyone understands why. This is where targeted door performance testing earns its place, sizing the test programme to what the project genuinely requires.

Safety in use is the other common gap. Impact classification and the strength of restraint devices are easy to overlook on a window admired for its slim sightlines, yet they are exactly what protects an occupant who stumbles against the glass or leans on an open sash. Operating forces matter too, especially for large or high-level units that a user has to open by hand. None of this surfaces unless the characteristics are chosen and tested deliberately at the design stage.

Bringing the testing and the marking together early, rather than treating the laboratory as a final box to tick, is what separates a clean handover from a stalled one. Deciding which characteristics your product has to declare, and in which classes, before the first unit reaches a rig is the difference between one planned test campaign and a string of reactive retests. Eurocert runs the EN 14351 testing and CE marking work from end to end, setting the test scope against the markets and projects you are actually chasing rather than a generic checklist.