+---
+title: Louvers and Dampers
+category: Mechanical / Air Distribution
+toc_depth: 3
+description: >
+ When to use: Stationary exterior and interior louvers and the full range of air-control and life-safety dampers in commercial, institutional, and light-industrial buildings. Covers drainable-blade, storm-resistant (wind-driven-rain), sand-trap, acoustic, combination louver/damper, and penthouse/gooseneck louvers selected by free area and water-penetration class at the design intake velocity; air-control dampers (parallel- and opposed-blade) selected by AMCA 500-D leakage class; backdraft, gravity, and pressure-relief dampers; and the life-safety dampers required at rated barriers — fire dampers (UL 555), smoke dampers (UL 555S), combination fire/smoke dampers, and ceiling radiation dampers (UL 555C) — together with actuators, fusible and resettable links, sleeves, retaining angles, access, and the firestopping interface. Includes hurricane-zone (AMCA 540 / 550) and Florida/High-Velocity-Hurricane-Zone louver requirements and the AMCA Certified Ratings Program basis for ratings.
+ Not intended for: Fans and the fan-side dampers integral to packaged equipment (see [[sync/hvac-fans]]); ductwork, plenums, and duct-mounted accessories that are not dampers (see [[sync/hvac-ductwork]]); grilles, registers, and diffusers and their integral opposed-blade volume dampers, which are room air-distribution devices (see [[sync/hvac-air-distribution-devices]]); operable architectural sun-control louvers and screen walls without an air-handling function; and dampers furnished as a non-separable factory part of an air-handling unit or rooftop unit.
+---
+
+# Scope
+
+This specification covers exterior and interior louvers and air-control, backdraft, pressure-relief, and life-safety dampers, including their frames, blades, seals, screens, finishes, sleeves, actuators, operators, and the means by which they are installed, flashed, sealed, firestopped, and tested. The work includes drainable and storm-resistant louvers at outdoor-air intakes and exhaust openings, sand-trap and acoustic louvers where the service condition requires them, combination louver/damper assemblies, control dampers for outdoor-air, return-air, mixed-air, exhaust, and isolation service, backdraft and gravity dampers, barometric and counterweighted pressure-relief dampers, and the fire dampers, smoke dampers, combination fire/smoke dampers, and ceiling radiation dampers required by the building and mechanical codes where ducts and air openings penetrate fire-resistance-rated and smoke-resistant construction.
+
+A louver and a damper solve opposite problems and are often confused. A louver is a fixed (or, less commonly, operable) array of sloped blades whose job is to admit or exhaust air through a wall opening while keeping rain, snow, and debris out; it has no moving parts in the stationary case and provides no shutoff. A damper is a moving blade assembly whose job is to control, balance, isolate, or — in the life-safety case — block airflow. Many openings need both: a louver for weather protection at the wall face and a damper behind it for control or shutoff. The two are selected against entirely different performance standards — louvers against AMCA Standard 500-L (and 540/550 for hurricane exposure), dampers against AMCA Standard 500-D for leakage and pressure drop and UL 555/555S/555C for life-safety rating — and this standard keeps the two decisions distinct.
+
+Two selections govern most of this work and recur throughout the standard. For louvers, it is the water-penetration class at the design intake velocity: a louver is only as good as the airflow it can carry before it begins to admit water, and that point is fixed by the free area, blade geometry, and the intake velocity through the free area. For control dampers, it is the leakage class and the blade arrangement: a low-leakage outdoor-air damper saves conditioning energy every hour the system runs, and opposed-blade construction modulates far more linearly than parallel-blade. For life-safety dampers, the governing decisions are the code-required rating, the leakage class, and the elevated-temperature degradation rating, all of which follow from where the damper sits in the rated construction.
+
+# Referenced Standards
+
+Materials, ratings, fabrication, and installation shall comply with the latest adopted editions of the following standards and codes. Where the contract documents, the adopted building or mechanical code, a listing agency's published installation instructions, or a referenced standard conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing. Life-safety dampers shall be installed strictly in accordance with the conditions of their UL listing; nothing in this standard or on the drawings relieves the installer of any condition of the listing.
+
+| Standard | Title |
+|----------|-------|
+| ANSI/AMCA 500-L | Laboratory Methods of Testing Louvers for Rating (pressure drop, air leakage, water penetration, wind-driven rain, wind-driven sand) |
+| ANSI/AMCA 500-D | Laboratory Methods of Testing Dampers for Rating (air leakage, pressure drop, dynamic closure, operational torque, elevated temperature) |
+| ANSI/AMCA 540 | Test Method for Louvers Impacted by Wind-Borne Debris |
+| ANSI/AMCA 550 | Test Method for High-Velocity Wind-Driven-Rain-Resistant Louvers |
+| AMCA 511 | Certified Ratings Program — Product Rating Manual for Air Control Devices |
+| AMCA 512 | Listing Label Program |
+| UL 555 | Standard for Fire Dampers |
+| UL 555S | Standard for Smoke Dampers |
+| UL 555C | Standard for Ceiling Dampers (ceiling radiation dampers) |
+| UL 33 | Heat-Responsive Links for Fire-Protection Service (fusible links) |
+| NFPA 90A | Installation of Air-Conditioning and Ventilating Systems |
+| NFPA 92 | Standard for Smoke Control Systems |
+| NFPA 105 | Smoke Door Assemblies and Other Opening Protectives |
+| IBC | International Building Code (Section 717, ducts and air transfer openings) |
+| IMC | International Mechanical Code (Section 607, duct and transfer-opening protection) |
+| SMACNA | HVAC Duct Construction Standards (sleeves, breakaway connections, transverse joints at dampers) |
+| AAMA 2604 | Voluntary Specification, Performance Requirements and Test Procedures for High-Performance Organic Coatings on Aluminum Extrusions and Panels |
+| AAMA 2605 | Voluntary Specification, Performance Requirements and Test Procedures for Superior-Performing Organic Coatings on Aluminum Extrusions and Panels |
+| AAMA 611 | Voluntary Specification for Anodized Architectural Aluminum |
+| ASTM B209 | Aluminum and Aluminum-Alloy Sheet and Plate |
+| ASTM A653 | Steel Sheet, Zinc-Coated (Galvanized) by the Hot-Dip Process |
+| Florida Building Code / TAS 201, 202, 203 | High-Velocity Hurricane Zone impact and pressure test protocols (where the project is in an HVHZ) |
+
+# Submittals
+
+## Action Submittals
+
+The Contractor shall submit the following for the Engineer's review and return before procurement and installation. Performance ratings shall be substantiated by laboratory data; where a product bears the AMCA Certified Ratings Program (CRP) seal, the CRP rating is the basis of acceptance and uncertified manufacturer-claimed ratings shall not be substituted.
+
+- Product data for each louver type, showing the model, depth, blade profile and spacing, free area at the scheduled size, the AMCA 500-L pressure-drop curve and the beginning-point-of-water-penetration intake velocity, the AMCA 500-L wind-driven-rain class or the AMCA 540/550 ratings where hurricane exposure applies, and confirmation of AMCA CRP licensing for the rated characteristics
+- Product data for each control, backdraft, and pressure-relief damper, showing blade arrangement (parallel or opposed), the AMCA 500-D leakage class with the leakage rate in ft³/min per ft² at 1 in. wg, the pressure-drop curve, the maximum rated pressure and velocity, blade and jamb seal materials, and frame and blade materials and gauges
+- Product data for each fire, smoke, combination fire/smoke, and ceiling radiation damper, showing the UL listing (UL 555, 555S, and/or 555C), the fire-resistance rating (1.5 hr or 3 hr), the static or dynamic rating with the rated airflow velocity and differential pressure, the UL 555S smoke leakage class (I, II, III) and the elevated-temperature degradation rating (250 °F or 350 °F), and the specific listed installation details (sleeve, retaining angle, mounting orientation)
+- An actuator and operator schedule listing, for each motorized damper, the actuator type (electric or pneumatic), action (two-position or modulating), fail-safe (spring-return open, spring-return closed, or non-spring-return), required torque, control signal, and power, coordinated with [[sync/building-automation-system]]
+- Shop drawings showing louver elevations and sizes coordinated to the wall openings, mullion and support locations, sill and head flashing details, the damper schedule with each tag cross-referenced to its location and rated barrier, and the sleeve, retaining-angle, breakaway, and access-door details for each life-safety damper
+- Finish samples for architectural louvers showing the AAMA 2604 or 2605 coating or AAMA 611 anodize, color, and gloss
+
+```datasheet
+label: Action Submittals Required
+type: checkbox
+options:
+ - "Louver product data with AMCA 500-L pressure drop and water-penetration data"
+ - "Louver AMCA 540/550 hurricane ratings (where applicable)"
+ - "Control/backdraft/relief damper product data with AMCA 500-D leakage class"
+ - "Life-safety damper product data with UL 555/555S/555C listing details"
+ - "Actuator and operator schedule"
+ - "Shop drawings (louver elevations, flashing, damper schedule, sleeve/access details)"
+ - "Finish samples (AAMA 2604/2605 or AAMA 611)"
+default: "Louver product data with AMCA 500-L pressure drop and water-penetration data"
+```
+
+## Closeout Submittals
+
+At substantial completion, the Contractor shall provide operation and maintenance data for all motorized and life-safety dampers, including the actuator data sheets, the fusible-link temperature rating and replacement part number, the resettable-link reset procedure where used, and the location of every concealed life-safety damper keyed to the access doors that serve it. The Contractor shall also provide the signed operational and leakage test reports required under Testing, and as-built drawings showing the final location and tag of every fire, smoke, and combination damper for the building's required periodic inspection and testing program.
+
+# Quality Assurance
+
+## Certified Ratings
+
+Louver and damper aerodynamic and leakage ratings used for selection shall be established under the AMCA Certified Ratings Program and shall bear the AMCA CRP seal for the rated characteristics (air performance, water penetration, and where applicable air leakage and wind-driven rain). The CRP seal certifies that the published ratings were obtained by the AMCA 500-L or 500-D laboratory method and independently verified, which is what allows a specifier to compare one manufacturer's louver against another on an equal basis. Ratings claimed by a manufacturer without CRP licensing for the specific characteristic shall not be accepted as equivalent.
+
+## Listing and Labeling of Life-Safety Dampers
+
+Every fire, smoke, combination fire/smoke, and ceiling radiation damper shall bear the label of a nationally recognized testing laboratory showing the applicable UL listing (UL 555, UL 555S, UL 555C), the fire-resistance rating, the static or dynamic rating, and for smoke and combination dampers the leakage class and elevated-temperature rating. The label shall remain legible and accessible after installation. An unlabeled or illegibly labeled life-safety damper shall be rejected; field repair or relabeling is not permitted.
+
+## Qualifications
+
+Louvers and dampers shall be the products of manufacturers regularly engaged in their production and participating in the AMCA CRP. Life-safety dampers shall be installed by a contractor experienced in installing UL-listed dampers in rated construction. The firestopping interface at life-safety damper penetrations shall be installed in coordination with [[sync/firestopping]].
+
+# Environmental and Service Conditions
+
+## Exposure and Intake Velocity
+
+Louver selection depends first on the exposure and on the air velocity through the louver free area at the design airflow. Water penetration through any louver rises sharply once the intake velocity exceeds the louver's beginning point of water penetration; selecting a louver means selecting one whose rated water-penetration velocity exceeds the actual design velocity through its free area with margin. Because free area is a fraction of the gross opening, the velocity through the free area is always higher than the face velocity, and undersizing the gross opening to save wall space is the most common cause of water carryover into the intake plenum.
+
+```datasheet
+label: Service Exposure
+type: radio
+options:
+ - "Standard exterior intake/exhaust, conventional rain exposure (most projects)"
+ - "Severe wind-driven-rain exposure, coastal or storm-prone (AMCA 550)"
+ - "Hurricane / High-Velocity Hurricane Zone — impact and wind-driven rain (AMCA 540 + 550)"
+ - "Interior transfer or relief opening, no weather exposure"
+default: "Standard exterior intake/exhaust, conventional rain exposure (most projects)"
+```
+
+```datasheet
+label: Design Intake Velocity Through Louver Free Area
+type: range
+unit: ft/min (fpm)
+drawing_ref: true
+options:
+ min: 400
+ max: 1200
+ setpoints: [400, 500, 600, 700, 800, 900, 1000, 1200]
+default: 800
+```
+
+```datasheet
+label: Damper Maximum Operating Differential Pressure
+type: range
+unit: in. wg
+options:
+ min: 1
+ max: 10
+ setpoints: [1, 2, 3, 4, 6, 8, 10]
+default: 4
+```
+
+# Louvers
+
+## Louver Type
+
+Drainable-blade louvers are the default for most exterior intake and exhaust openings: each blade has a downward-sloped front lip and a gutter that catches intercepted water and carries it to channels in the jambs that drain it down and out at the sill, so water that hits the blade face is collected and shed rather than blown through. Storm-resistant (wind-driven-rain) louvers use a deeper section, often with a hooked blade or a dual bank of blades, and are AMCA-rated for performance in driven rain at high face velocities; they protect mission-critical intakes (data centers, hospitals, emergency power rooms) where any water carryover is unacceptable. Sand-trap louvers use inertial blade geometry to drop wind-borne sand out of the airstream before it reaches the equipment and are specified in desert and arid environments. Acoustic louvers contain sound-absorbing blade infill to attenuate noise breaking out of or into the opening and are used where the opening faces a noise-sensitive receptor. Combination louver/damper assemblies integrate a control or backdraft damper directly behind the louver in one frame where wall depth is limited. Penthouse and gooseneck louvers are roof-mounted hooded intakes and exhausts that protect a vertical roof opening.
+
+```datasheet
+label: Louver Type
+type: select
+options:
+ - "Stationary drainable-blade (standard exterior intake/exhaust)"
+ - "Storm-resistant / wind-driven-rain (mission-critical or severe exposure)"
+ - "Sand-trap (arid / wind-borne sand environments)"
+ - "Acoustic (noise-sensitive openings)"
+ - "Combination louver with integral control or backdraft damper"
+ - "Penthouse / gooseneck (roof-mounted hooded opening)"
+default: "Stationary drainable-blade (standard exterior intake/exhaust)"
+```
+
+## Water-Penetration Class
+
+The water-penetration class fixes the intake velocity through the free area at which water begins to penetrate the louver under the AMCA 500-L test. A higher class permits a higher velocity (a smaller louver) before carryover begins. The class shall be selected so that its beginning-point-of-water-penetration velocity exceeds the design intake velocity through the free area; a Class A louver admits essentially no water below its rated velocity and is the appropriate choice for intakes serving conditioned and equipment spaces.
+
+```datasheet
+label: AMCA 500-L Water-Penetration Class
+type: radio
+options:
+ - "Class A — no water penetration up to the rated velocity (intakes to conditioned/equipment spaces)"
+ - "Class B — minimal penetration above the rated velocity (general intake/exhaust)"
+ - "Class C — higher penetration (non-critical exhaust where minor carryover is acceptable)"
+default: "Class A — no water penetration up to the rated velocity (intakes to conditioned/equipment spaces)"
+```
+
+## Free Area
+
+Free area is the net open area through which air actually passes and is the basis for the velocity calculation that drives both pressure drop and water penetration. Louver free area shall be the AMCA-certified free area for the scheduled size, not a nominal percentage, because free area falls as a louver is made smaller (frame and mullions consume a fixed area). The minimum free area shall be coordinated so the design airflow does not drive the free-area velocity above the selected water-penetration class's rated velocity.
+
+```datasheet
+label: Minimum Certified Free Area
+type: range
+unit: % of gross wall opening
+options:
+ min: 35
+ max: 60
+ setpoints: [35, 40, 45, 50, 55, 60]
+default: 45
+```
+
+## Wind-Driven Rain and Impact Rating
+
+In severe-exposure and hurricane-zone applications, ordinary water-penetration class is insufficient because driven rain arrives with both high velocity and a horizontal component. AMCA 550 rates a louver's ability to reject high-velocity wind-driven rain at hurricane wind speeds, and AMCA 540 rates a louver's resistance to wind-borne debris impact (a 2×4 timber fired from an air cannon at the longest and shortest unsupported blade spans). Where the project lies in a designated High-Velocity Hurricane Zone, the louver shall additionally carry the Florida Building Code / Miami-Dade product approval based on the TAS protocols.
+
+```datasheet
+label: Wind-Driven-Rain / Impact Rating (severe-exposure and hurricane zones)
+type: radio
+options:
+ - "Not required — standard exposure"
+ - "AMCA 550 high-velocity wind-driven-rain rated"
+ - "AMCA 540 + 550 (impact and wind-driven rain) for hurricane zones"
+ - "AMCA 540 + 550 plus Florida/HVHZ (Miami-Dade) product approval"
+default: "Not required — standard exposure"
+```
+
+## Frame, Blade Material, and Depth
+
+Extruded-aluminum louvers (ASTM B209 alloy) are the architectural standard: light, corrosion-resistant, and available in deep storm-resistant profiles. Galvanized or stainless steel louvers are used for industrial, high-temperature, or high-abuse service. Louver depth follows the type and rating — a 4 in. drainable louver suits standard exposure, while storm-resistant and hurricane louvers are typically 5 in. to 6 in. or deeper.
+
+```datasheet
+label: Louver Frame and Blade Material
+type: radio
+options:
+ - "Extruded aluminum (ASTM B209) — architectural standard"
+ - "Galvanized steel (ASTM A653) — industrial / high-abuse"
+ - "Stainless steel — corrosive or high-temperature service"
+default: "Extruded aluminum (ASTM B209) — architectural standard"
+```
+
+```datasheet
+label: Louver Depth
+type: select
+unit: in.
+options:
+ - "2 in. — shallow interior or low-performance"
+ - "4 in. — standard drainable-blade exterior"
+ - "5 in. — high-performance / storm-resistant"
+ - "6 in. — deep storm-resistant / hurricane"
+default: "4 in. — standard drainable-blade exterior"
+```
+
+## Finish
+
+Exposed architectural louvers shall receive a factory finish matched to the building envelope. A 70% PVDF fluoropolymer coating meeting AAMA 2605 is the premium choice for long exterior life and color/gloss retention; a 50% PVDF or comparable coating meeting AAMA 2604 is the standard choice; anodize to AAMA 611 is used where a metallic appearance is wanted. Color shall be as selected by the Architect and shall be coordinated with [[sync/sheet-metal-flashing-and-trim]] where the louver abuts metal flashing or panel.
+
+```datasheet
+label: Louver Finish
+type: radio
+options:
+ - "70% PVDF fluoropolymer, AAMA 2605 (premium exterior, best color retention)"
+ - "50% PVDF / organic coating, AAMA 2604 (standard exterior)"
+ - "Architectural anodize, AAMA 611"
+ - "Mill finish (concealed or industrial, non-architectural)"
+default: "50% PVDF / organic coating, AAMA 2604 (standard exterior)"
+```
+
+## Screens
+
+Louvers shall be furnished with a removable rear screen sized to the opening. Bird screen (½ in. or ¾ in. mesh) is the default for exterior openings; insect screen (fine mesh) is specified where insect intrusion must be prevented but adds pressure drop and clogs faster. Screens shall be aluminum or stainless to match the corrosion class and shall be in a removable frame for cleaning.
+
+```datasheet
+label: Louver Screen
+type: radio
+options:
+ - "Bird screen, 1/2 in. mesh, removable frame (standard exterior)"
+ - "Bird screen, 3/4 in. mesh"
+ - "Insect screen, fine mesh (where insect intrusion must be prevented)"
+ - "No screen (interior or where downstream device provides screening)"
+default: "Bird screen, 1/2 in. mesh, removable frame (standard exterior)"
+```
+
+Louver sizes, locations, and quantities shall be [[drawing: as indicated on the louver schedule and exterior elevations]].
+
+# Control Dampers
+
+## Blade Arrangement
+
+The single most consequential control-damper decision is parallel- versus opposed-blade construction, and it follows from how the damper is controlled. In a parallel-blade damper all blades rotate the same direction, so the open damper deflects the airstream to one side; the flow-versus-position curve is steeply nonlinear, with most of the flow change crowded into the first part of travel. In an opposed-blade damper adjacent blades rotate in opposite directions, splitting and re-centering the airstream; the flow-versus-position relationship is far more linear, which is what a modulating control loop needs to stay stable across its range. Use opposed-blade dampers for modulating service (outdoor-air, mixed-air, and any damper a controller throttles), and parallel-blade dampers for two-position (open/closed) isolation and shutoff service, where the better linearity is not needed and the parallel blade's tighter closed-position seal and lower cost are an advantage. Where a parallel-blade damper discharges into a downstream coil or filter, orienting the blades so they throw air toward the duct wall rather than directly at the device improves downstream air distribution.
+
+```datasheet
+label: Control Damper Blade Arrangement
+type: radio
+options:
+ - "Opposed-blade — modulating service (outdoor-air, mixed-air, throttled control)"
+ - "Parallel-blade — two-position isolation/shutoff service"
+default: "Opposed-blade — modulating service (outdoor-air, mixed-air, throttled control)"
+```
+
+## Leakage Class
+
+Damper closed-position leakage is rated by the AMCA 500-D method and expressed as a leakage class. The class matters most on outdoor-air and exhaust dampers that close when the system is off or in minimum-outdoor-air mode: every cubic foot per minute that leaks past a closed outdoor-air damper is unconditioned air the system must later heat or cool, and over a building's life a low-leakage damper repays its modest premium many times over in conditioning energy. A low-leakage (ultra-low-leakage) damper at AMCA Class 1A leaks no more than about 3 ft³/min·ft² at 1 in. wg; Class 1 no more than about 4; Class 2 no more than about 10; Class 3 no more than about 40. Outdoor-air and exhaust dampers that seal the building envelope shall be Class 1A or Class 1; interior balancing and mixing dampers that never fully isolate may be Class 2 or 3.
+
+```datasheet
+label: Control Damper Leakage Class (AMCA 500-D, at 1 in. wg)
+type: radio
+options:
+ - "Class 1A — ultra-low leakage, ≤ 3 ft³/min·ft² (outdoor-air/exhaust isolation, energy-code envelope dampers)"
+ - "Class 1 — low leakage, ≤ 4 ft³/min·ft² (general isolation)"
+ - "Class 2 — ≤ 10 ft³/min·ft² (interior mixing/balancing)"
+ - "Class 3 — ≤ 40 ft³/min·ft² (non-isolating throttling only)"
+default: "Class 1A — ultra-low leakage, ≤ 3 ft³/min·ft² (outdoor-air/exhaust isolation, energy-code envelope dampers)"
+```
+
+## Blade and Jamb Seals
+
+Low leakage is achieved by the seals, not the blades. Blade-edge seals (extruded silicone, EPDM, or a mechanically captured elastomer) and stainless or galvanized compressible jamb seals close the gaps at the blade edges and at the frame jambs when the damper is shut. The seals shall be mechanically fastened or captured, not adhesive-applied, so they cannot peel off in the airstream, and shall be rated for the service temperature. Outdoor-air dampers in cold climates shall have seals rated for low-temperature service so they remain pliable and do not crack and leak when cold.
+
+```datasheet
+label: Damper Seals
+type: checkbox
+options:
+ - "Elastomeric blade-edge seals (silicone / EPDM)"
+ - "Compressible stainless or galvanized jamb seals"
+ - "Low-temperature-rated seals (cold-climate outdoor-air dampers)"
+ - "High-temperature-rated seals (elevated-temperature service)"
+default: "Elastomeric blade-edge seals (silicone / EPDM)"
+```
+
+## Frame and Blade Construction
+
+Control damper frames shall be galvanized steel or extruded aluminum of a gauge and section suited to the size and the maximum operating pressure, with blades of an airfoil or formed section. Airfoil blades give lower pressure drop and lower required actuator torque than flat formed blades and are preferred on large dampers and on outdoor-air dampers where pressure drop is an energy penalty. Blade and frame materials shall match the airstream's corrosion class; aluminum or stainless construction is used in corrosive or high-humidity exhaust.
+
+```datasheet
+label: Control Damper Frame and Blade Material
+type: radio
+options:
+ - "Galvanized steel frame, airfoil galvanized steel blades (standard)"
+ - "Extruded aluminum frame and airfoil blades (low pressure drop / corrosion service)"
+ - "Stainless steel (corrosive exhaust)"
+default: "Galvanized steel frame, airfoil galvanized steel blades (standard)"
+```
+
+# Backdraft and Pressure-Relief Dampers
+
+## Backdraft / Gravity Dampers
+
+A backdraft (gravity) damper allows airflow in one direction and closes by gravity or a light spring when flow reverses or stops, preventing outdoor air, exhaust, or air from a parallel fan from back-flowing through an idle opening. It is the right device at an exhaust-fan discharge, a relief opening, or any opening that must pass air one way and stay shut the other without a powered actuator. Counterbalanced (adjustable counterweight) backdraft dampers are used where the opening pressure must be tuned so the damper opens at a low, repeatable pressure rather than fluttering.
+
+```datasheet
+label: Backdraft Damper Type
+type: radio
+options:
+ - "Gravity backdraft (closes by blade weight on flow reversal) — standard exhaust/relief"
+ - "Counterbalanced backdraft (adjustable counterweight for low/tuned opening pressure)"
+ - "Spring-assisted backdraft (positive closure against light reverse pressure)"
+default: "Gravity backdraft (closes by blade weight on flow reversal) — standard exhaust/relief"
+```
+
+## Pressure-Relief Dampers
+
+A barometric pressure-relief damper opens automatically when the space or duct pressure exceeds a set point, relieving overpressure (for example, on building pressurization, on a gas suppression discharge, or to relieve a fan dead-heading). The relief set point shall be field-adjustable by counterweight or spring and shall be set and recorded during balancing.
+
+```datasheet
+label: Pressure-Relief Set Point
+type: range
+unit: in. wg
+drawing_ref: true
+options:
+ min: 0.05
+ max: 1.0
+ setpoints: [0.05, 0.1, 0.15, 0.25, 0.5, 0.75, 1.0]
+default: 0.25
+```
+
+# Fire, Smoke, and Combination Dampers
+
+## Code Trigger and Damper Type
+
+Life-safety dampers are required by the building and mechanical codes wherever a duct or air-transfer opening penetrates a fire-resistance-rated or smoke-resistant assembly. A fire damper (UL 555) is required where the duct penetrates a fire wall, fire barrier, fire partition, shaft, or rated horizontal assembly; it stays open in normal operation and closes when its heat-responsive (fusible) link releases or a heat detector signals, blocking the passage of fire. A smoke damper (UL 555S) is required where the duct penetrates a smoke barrier or serves a smoke-control function; it closes on a signal from the fire-alarm or smoke-control system to block the migration of smoke. A combination fire/smoke damper meets both UL 555 and UL 555S and is required where a single penetration crosses construction that is both fire-rated and smoke-resistant — the common case at smoke-barrier corridors and at floor/shaft penetrations. A ceiling radiation damper (UL 555C) protects an air opening in a fire-resistance-rated floor/ceiling or roof/ceiling membrane. The required damper type follows directly from the rated assembly being penetrated and shall be coordinated against the [[drawing: life-safety plan and the rated-assembly schedule]].
+
+```datasheet
+label: Life-Safety Damper Type
+type: select
+options:
+ - "Fire damper (UL 555) — penetration of fire wall/barrier/partition/shaft"
+ - "Smoke damper (UL 555S) — penetration of smoke barrier / smoke-control duct"
+ - "Combination fire/smoke damper (UL 555 + UL 555S) — fire-rated and smoke-resistant penetration"
+ - "Ceiling radiation damper (UL 555C) — opening in rated floor/ceiling or roof/ceiling membrane"
+default: "Combination fire/smoke damper (UL 555 + UL 555S) — fire-rated and smoke-resistant penetration"
+```
+
+## Fire-Resistance Rating
+
+The damper's fire-resistance rating shall match the rating of the assembly it protects. A 1.5-hour-rated fire damper is required in assemblies rated less than 3 hours; a 3-hour-rated fire damper is required in assemblies rated 3 hours or more. Selecting a 1.5-hour damper for a 3-hour wall is a code violation that will fail inspection.
+
+```datasheet
+label: Fire Damper Fire-Resistance Rating
+type: radio
+options:
+ - "1.5 hour — for assemblies rated less than 3 hours (most fire barriers/partitions/shafts)"
+ - "3 hour — for assemblies rated 3 hours or more"
+default: "1.5 hour — for assemblies rated less than 3 hours (most fire barriers/partitions/shafts)"
+```
+
+## Static vs. Dynamic Rating
+
+A static fire damper is listed to close under no-flow conditions and is permitted only where the HVAC system is automatically shut down on a fire signal, so the damper closes into still air. A dynamic fire damper is tested and labeled to close against a rated airflow velocity and differential pressure and is required wherever the system fan continues to run during a fire event — including most engineered smoke-control and stairwell-pressurization systems. Because a dynamic damper also satisfies static applications, dynamic-rated dampers are a safe default where the operating mode is uncertain, provided the rated velocity and pressure envelope the actual system conditions.
+
+```datasheet
+label: Fire/Combination Damper Closure Rating
+type: radio
+options:
+ - "Dynamic — closes against rated airflow and pressure (system fan runs during fire / uncertain)"
+ - "Static — closes in no-flow only (HVAC shuts down automatically on fire signal)"
+default: "Dynamic — closes against rated airflow and pressure (system fan runs during fire / uncertain)"
+```
+
+```datasheet
+label: Dynamic Damper Rated Closure Velocity
+type: range
+unit: ft/min (fpm)
+options:
+ min: 2000
+ max: 4000
+ setpoints: [2000, 3000, 4000]
+default: 4000
+```
+
+## Smoke Leakage Class
+
+Smoke and combination dampers carry a UL 555S smoke leakage class. Class I is the tightest (about 4 ft³/min·ft² at 1 in. wg), Class II is intermediate (about 10), and Class III is the loosest (about 40). The building and mechanical codes require smoke dampers to be Class I or Class II; Class I is the appropriate default for smoke barriers and smoke-control service where leakage tightness directly limits smoke migration.
+
+```datasheet
+label: Smoke Damper Leakage Class (UL 555S)
+type: radio
+options:
+ - "Class I — ≤ 4 ft³/min·ft² at 1 in. wg (smoke barriers, smoke control)"
+ - "Class II — ≤ 10 ft³/min·ft² at 1 in. wg (where permitted)"
+default: "Class I — ≤ 4 ft³/min·ft² at 1 in. wg (smoke barriers, smoke control)"
+```
+
+## Elevated-Temperature Degradation Rating
+
+A smoke damper must keep closing and keep sealing while the air moving through it is hot, so UL 555S assigns an elevated-temperature degradation rating: the damper is tested to operate and hold its leakage class with airflow at the rated temperature. The code minimum is 250 °F; a 350 °F rating is specified where the smoke-control design or the authority having jurisdiction requires the damper to function at higher temperatures, and it is the prudent choice for engineered smoke-control systems where the damper may see hotter smoke.
+
+```datasheet
+label: Smoke Damper Elevated-Temperature Rating (UL 555S)
+type: radio
+options:
+ - "250 °F — code minimum (general smoke-barrier service)"
+ - "350 °F — engineered smoke control / higher AHJ requirement"
+default: "250 °F — code minimum (general smoke-barrier service)"
+```
+
+## Release and Reset
+
+A fire damper closes when its heat-responsive link releases. A fusible link (UL 33) of the rated temperature melts and frees the closure spring; it is single-use and must be replaced after any actuation. A resettable (electric/electronic) link allows the damper to be tested and reset without replacing a component and is required on combination fire/smoke dampers, which must cycle on command and on signal from the fire-alarm and smoke-control system. The fusible-link or release temperature shall be selected for the operating air temperature — a standard 165 °F link for ordinary systems, a higher-temperature link where the normal duct temperature would otherwise nuisance-release a standard link.
+
+```datasheet
+label: Heat-Responsive Release
+type: radio
+options:
+ - "Fusible link, 165 °F (UL 33) — standard fire damper, ordinary duct temperature"
+ - "Fusible link, 212 °F or higher — elevated normal duct temperature"
+ - "Resettable electronic link with actuator — combination fire/smoke and testable dampers"
+default: "Resettable electronic link with actuator — combination fire/smoke and testable dampers"
+```
+
+Fire, smoke, and combination damper locations, tags, and the rated assembly each protects shall be [[drawing: as indicated on the damper schedule and life-safety plans]].
+
+# Actuators and Operators
+
+## Actuator Type and Action
+
+Motorized dampers shall be furnished with the actuator scheduled for their service. Electric actuators are the default for new work and integrate directly with [[sync/building-automation-system]]; pneumatic actuators are used where an existing pneumatic control infrastructure is being extended. Two-position actuators drive a damper fully open or fully closed for isolation and shutoff service; modulating (proportional) actuators position the damper anywhere across its travel in response to a control signal and are required for any throttled outdoor-air, mixed-air, or pressure-control damper.
+
+```datasheet
+label: Actuator Type
+type: radio
+options:
+ - "Electric (24 VAC or line voltage) — standard for new work"
+ - "Pneumatic — extension of existing pneumatic controls"
+default: "Electric (24 VAC or line voltage) — standard for new work"
+```
+
+```datasheet
+label: Actuator Action
+type: radio
+options:
+ - "Modulating (proportional 0–10 VDC / 4–20 mA) — throttled outdoor-air/mixed-air/pressure control"
+ - "Two-position (open/closed) — isolation and shutoff"
+default: "Modulating (proportional 0–10 VDC / 4–20 mA) — throttled outdoor-air/mixed-air/pressure control"
+```
+
+## Fail-Safe Position
+
+The actuator's de-energized (fail-safe) position shall protect the system and the building when power or control is lost. Spring-return actuators drive the damper to a defined safe position on loss of power; outdoor-air dampers are normally specified spring-return-closed so a power loss does not admit unconditioned or freezing air, while life-safety damper actuators fail to their listed safe position (typically closed) on loss of power or on a fire-alarm signal. Non-spring-return actuators hold the last position and are used only where a defined fail-safe position is not required.
+
+```datasheet
+label: Actuator Fail-Safe Position
+type: radio
+options:
+ - "Spring-return closed (fail closed) — outdoor-air, isolation, life-safety dampers"
+ - "Spring-return open (fail open) — relief/exhaust paths that must stay open on power loss"
+ - "Non-spring-return (holds last position) — where no fail-safe position is required"
+default: "Spring-return closed (fail closed) — outdoor-air, isolation, life-safety dampers"
+```
+
+## Torque Sizing
+
+The actuator shall develop sufficient torque to drive the damper fully closed against the maximum operating differential pressure and velocity and to seat the blade and jamb seals, with margin. Undersized actuators are a frequent cause of leaky dampers that never fully seat and of life-safety dampers that fail to close against system airflow. Required torque shall be based on the damper area, the seal type, and the maximum operating pressure per the damper manufacturer's torque tables.
+
+```datasheet
+label: Actuator Torque Basis
+type: radio
+options:
+ - "Per damper manufacturer torque table for area, seal type, and maximum operating pressure (standard)"
+ - "As scheduled on the actuator schedule"
+default: "Per damper manufacturer torque table for area, seal type, and maximum operating pressure (standard)"
+```
+
+# Installation
+
+## Louver Flashing, Sill, and Drainage
+
+A louver is a hole in the building envelope, and most louver failures are water failures at the perimeter, not through the blades. The Contractor shall install head and jamb flashing and a sloped sill pan that collects any water reaching the back of the louver — both water shed by the drainable blades and water that bypasses them in a storm — and drains it to the exterior, never into the wall cavity or the intake plenum. The perimeter shall be sealed continuously to the wall air and water barrier so wind-driven rain cannot track around the frame. The louver-to-wall joint shall be made watertight and airtight in coordination with [[sync/air-barriers]] and sealed with sealant conforming to [[sync/joint-sealants]]; head and sill flashing shall be coordinated with [[sync/sheet-metal-flashing-and-trim]]. Where the louver carries a blank-off panel behind an architecturally oversized opening, the blank-off shall be insulated and the air opening sized to the design free area.
+
+## Damper Sleeves and Retaining Angles
+
+Fire, smoke, and combination dampers shall be installed in a steel sleeve of the gauge and length required by the damper's UL listing, with retaining (mounting) angles attached to the sleeve and lapping the wall or floor on each side exactly as the listing requires. The retaining angle is what holds the damper in the opening when the surrounding duct burns away or moves under fire; an angle of the wrong size, fastened the wrong way, or omitted, voids the listing even though the damper itself is correct. The damper shall be installed in the orientation (vertical or horizontal blade) for which it is listed; many dampers are listed for one orientation only.
+
+```datasheet
+label: Life-Safety Damper Sleeve and Mounting
+type: radio
+options:
+ - "Steel sleeve with retaining angles per the damper's UL listing (mandatory)"
+default: "Steel sleeve with retaining angles per the damper's UL listing (mandatory)"
+```
+
+## Breakaway Connections
+
+The duct-to-sleeve connection at a fire or combination damper shall be a breakaway connection of the type and size permitted by the damper's listing, so that when the duct is exposed to fire and distorts or falls, it separates from the damper without pulling the damper out of the rated opening. Rigid (non-breakaway) connections shall be used only where specifically permitted by the listing. Transverse joints and connections shall otherwise comply with the applicable SMACNA construction standard.
+
+## Access Doors
+
+Every fire, smoke, and combination damper shall be served by an access door in the duct or the construction, of adequate size and located so the link, actuator, and blade can be reached for the required periodic inspection, testing, and resetting. Concealed dampers with no access cannot be tested and will fail the building's inspection program. Access doors shall be labeled to identify the life-safety damper behind them.
+
+```datasheet
+label: Damper Access
+type: radio
+options:
+ - "Labeled access door at every fire/smoke/combination damper for inspection, test, and reset (required)"
+default: "Labeled access door at every fire/smoke/combination damper for inspection, test, and reset (required)"
+```
+
+## Firestopping Interface
+
+The annular space between the damper sleeve and the rated wall or floor shall be firestopped, and any clearance the listing requires around the sleeve shall be maintained, in accordance with the damper's listing and [[sync/firestopping]]. The firestop and the damper listing are interdependent; the Contractor shall use the firestop system and the clearance that the damper's listing references and shall not substitute an unlisted detail.
+
+# Testing
+
+## Operational Test of Life-Safety Dampers
+
+Before substantial completion, every fire, smoke, and combination fire/smoke damper shall be operationally tested under the conditions of its listing and the code: each damper shall be cycled to confirm it fully closes and (for smoke and combination dampers) reopens on command, that resettable links reset, and that fusible-link dampers release and reseat when manually tripped. Combination and smoke dampers shall be verified to close on the signal from the fire-alarm and smoke-control systems in coordination with the fire-alarm and [[sync/building-automation-system]] commissioning. Each damper test shall be documented with the damper tag, location, and result.
+
+```datasheet
+label: Life-Safety Damper Operational Test
+type: checkbox
+options:
+ - "Cycle each damper full-closed and confirm full closure"
+ - "Verify smoke/combination dampers close on fire-alarm / smoke-control signal"
+ - "Verify resettable links reset and fusible-link dampers reseat after trip"
+ - "Document each test by damper tag and location"
+default: "Cycle each damper full-closed and confirm full closure"
+```
+
+## Control Damper Leakage and Operation
+
+Control dampers shall be verified during balancing to stroke fully open and fully closed, to seat their seals, and — for outdoor-air and isolation dampers specified to a leakage class — to close with no audible leakage and to seat against the maximum operating pressure. Actuators shall be confirmed to drive to the correct fail-safe position on loss of power and control signal.
+
+# Cleaning and Protection
+
+Louvers and dampers shall be protected during construction from mortar, paint overspray, drywall dust, and mechanical damage; a louver fouled with construction debris loses free area and may clog its sill drainage. Before substantial completion, louvers, screens, and exposed finishes shall be cleaned without damaging the finish, sill drainage channels shall be cleared, and any damaged finish shall be repaired or the component replaced. Damper blades, seals, and linkages shall be left clean and free of debris that would prevent full closure.
+
+# Warranty
+
+The Contractor shall warrant the louver and damper installation against defects in materials and workmanship, and against water penetration attributable to the louver selection or its perimeter flashing and sealing, for a period of not less than two years from substantial completion, or for the period stated in the contract documents if longer. Factory finishes on architectural louvers shall carry the coating manufacturer's standard finish warranty (typically not less than 20 years for AAMA 2605 fluoropolymer finishes). Any life-safety damper that fails to operate as listed, and any control damper that fails to achieve its specified leakage class at full closure, shall be corrected at the Contractor's expense.