Choosing an exterior louver begins with its job, not its material. A solar screen, ventilation intake, rain-control opening, privacy layer and plant enclosure may look similar in elevation, yet each is judged by different evidence. Define the priority, model the trade-offs and only then compare blade geometry, support and material.
Classify the louver’s primary function
Write a short performance brief for every louver zone. A shading screen should identify the glazing and occupied hours it protects. A ventilation louver needs required airflow, allowable pressure drop and weather exposure. A visual screen needs view angles and openness. Acoustic, security, impact, fire or severe-weather functions introduce further criteria and may require specialist products.
Do not combine unrelated promises into one label. The original 2015 article presented louvers mainly as devices that admit clean fresh air while keeping debris and water out, then quoted a generic 35%–60% free-area range. That range is archived guidance, not a selection rule. Performance depends on tested size, blade configuration, airflow condition and project acceptance criteria.
Test solar control against orientation
For shading, use the building coordinates, facade orientation, glazing, adjacent obstructions and occupied schedule. Horizontal blades may control some high-angle sun, while vertical elements can be useful for lower-angle sun from the sides. East and west exposures often need particular attention because low sun can pass beneath a shallow horizontal projection.
Compare depth, pitch, angle, spacing and screen offset through solar, daylight and glare analysis. A denser screen may reduce direct sun but also darken the interior, obstruct views and increase artificial-lighting demand. The U.S. Department of Energy’s daylighting guidance identifies louvers and screens as tools for unwanted heat and glare control; it does not imply a universal energy saving. Results belong to the complete window and building model.
Set visual and privacy criteria
From outside
Study rhythm, depth, support visibility, corner transitions, backgrounds and how the screen changes between daylight and facade lighting.
From inside
Check seated and standing sightlines, glare, perceived enclosure, window-cleaning access and whether blade edges interrupt important views.
At an angle
A screen that appears open head-on may become opaque obliquely. Test approach routes and privacy sightlines with full-scale geometry.
Over time
Consider finish weathering, dirt patterns, staining below joints, replacement colour and how visible repairs will be.
A full-scale mock-up is more reliable than a rendering for judging depth and transparency. Include the real background, support colour, perimeter, lighting and a representative opening. Record the approved view angles and material range rather than approving one isolated blade.
For ventilation, compare tested air and rain data
Free area is useful but does not by itself predict airflow, water entry or system energy. Compare pressure drop at the required airflow using consistent louver sizes and test conditions. Include screens, filters, dampers, duct transitions and nearby obstructions in the mechanical design; upstream and downstream conditions can change performance.
Rain control is also conditional. Define ordinary water penetration, wind-driven rain or severe-weather requirements as appropriate, and provide drainage behind the opening. The AMCA louver application manual addresses pressure drop, leakage, water penetration and system effects. Its associated laboratory methods provide rating procedures; the project team must still set acceptable values.
These ventilation tests should not be assumed for an open architectural sunscreen. Conversely, a weather-rated mechanical louver may not deliver the desired solar geometry or architectural expression. Identify where the two functions overlap and where separate layers are safer.
Engineer blades, frames and attachments
Determine wind, self-weight, seismic and maintenance actions with the project engineer. Review blade span and deflection, frame movement, fasteners, anchors, support reactions and substrate capacity. Operable systems add pivots, actuators, controls, fail position, commissioning and safe access. Account for ice, snow or impact where the location demands it.
Material selection affects section size, weight, finish, corrosion strategy, thermal movement and achievable span. Aluminium, steel, fired clay and other materials should be compared through project-specific evidence, not one generic durability ranking. Dissimilar-metal interfaces and runoff paths require coordination. A brittle ceramic element needs a different connection and handling approach from a formed metal blade.
Plan cleaning, inspection and replacement
Decide how workers will reach both blade faces, perimeter seals, drains, fasteners and glazing behind. Horizontal surfaces can collect dust; closely spaced or rotated blades can make cleaning difficult. Avoid creating inaccessible pockets around lights, bird-control devices or services. Provide safe removal clearances for a damaged blade.
Request cleaning instructions, finish repair limits, inspection frequency, spare parts and replacement lead times. For operable louvers, define functional testing and maintenance of actuators and sensors. A cheaper initial assembly can become costly if access equipment or dismantling is needed for routine work.
Use a decision matrix before selecting material
Score each option against the same project criteria: solar result, daylight and views, airflow and pressure drop where applicable, water rejection, structural capacity, fire and code duties, appearance range, maintenance access, replaceability, programme and whole-package cost. Mark evidence as calculated, tested, sampled or still unverified. This exposes assumptions before tender.
If fired clay suits the architectural and structural brief, review terracotta baguettes and louvers and the dedicated terracotta sunscreen overview. Those resources explain a material option; this decision framework remains applicable to every candidate.