Internal shaft baffles (pareh) and intake port geometries form the aerodynamic brain of the Iranian bâdgir. By dividing the tower's interior into four to eight isolated vertical shafts using thin brick and clay partitions, the tower simultaneously captures positive-pressure windward breezes and exhausts stale air via leeward negative-pressure suction.
At a Glance: Key Takeaways
- Baffle Masonry: Pareh (vertical brick and gypsum partition walls 10–12 cm thick)
- Shaft Configurations: Four-sided (chahar-taraf), eight-sided (hasht-taraf), and circular
- Fluid Principle: Bernoulli theorem creating simultaneous intake and exhaust paths
- Air Velocity Multiplier: Aperture constriction accelerating gentle breezes by 1.5x to 2.0x
The Aerodynamic Function of the Pareh Baffle
If a bâdgir were simply a hollow vertical chimney, wind blowing across the top opening would create turbulence and backdrafts, preventing air from descending to ground level. The breakthrough of Persian engineers was the invention of internal partition baffles known as pareh or tiqeh.
Constructed from lightweight kiln-fired clay bricks bedded in quick-setting gypsum mortar, the baffles run continuously from the top intake vents all the way down to the living rooms. The baffles form completely isolated vertical ducts that prevent descending fresh air from colliding with ascending exhaust air.
Four-Sided vs Eight-Sided Tower Geometries
Bâdgir designs vary based on local geographic wind characteristics:
- Uni-Directional (One-Sided): Found in regions like Meybod, where clean winds blow reliably from a single direction and opposing winds carry blinding desert sand. The tower has openings on only one side.
- Four-Sided (Chahar-Taraf): The most common domestic design in Yazd and Kashan. An internal X-shaped or cross-shaped baffle divides the square tower into four independent vertical flues.
- Eight-Sided (Hasht-Taraf): Reserved for grand aristocratic mansions and public water reservoirs (ab anbars). An octagonal perimeter combined with radial baffles captures breezes from any degree of the compass.
Bernoulli Suction and Dynamic Pressure Differentials
The simultaneous operation of intake and exhaust within the same tower is governed by the Bernoulli equation: P + 0.5*rho*V^2 = constant. When ambient wind strikes the windward vents, kinetic air energy is converted into static pressure, forcing air down the forward flues.
Simultaneously, wind accelerates as it rounds the leeward corners of the tower, creating a localized drop in atmospheric pressure. This partial vacuum sucks warm, stagnant air out of the building through the leeward flues, establishing continuous cross-room air renewal even when doors and windows remain closed.
Aperture Geometry and Bird-Deflecting Louvers
The top openings of the windcatcher are shaped with pointed Persian arches (chahar-qad) flanked by decorative projecting brick dentils. These narrow vertical slits act as venture nozzles, compressing and accelerating gentle desert breezes into brisk, refreshing drafts.
To prevent desert pigeons and bats from roosting inside the flues, masons installed angled wooden louver slats or pierced terracotta grilles. These grilles are angled downward at 45 degrees, blocking rain during winter showers while allowing wind to penetrate freely.
Bâdgir Shaft Configurations and Climatic Suitability
Use this reference table to calculate exact physical dimensions, ratios, and specifications before purchasing:
| Typology | Internal Flue Count | Optimal Wind Environment | Dust Exclusion Capability |
|---|---|---|---|
| Uni-Directional (Meybod style) | 1 single broad vertical flue | Fixed prevailing wind; severe dust storms on back | Exceptional; solid brick wall faces seasonal dust |
| Two-Sided (Do-Taraf) | 2 flues separated by central spine | Coastal breezes reversing between day and night | Good; easily throttled with interior wooden dampers |
| Four-Sided (Chahar-Taraf) | 4 flues divided by cross-shaped pareh | Inland desert oases with multi-directional breezes | Moderate; requires internal dust-settling chambers |
| Eight-Sided (Hasht-Taraf) | 8 radial flues with central spider baffle | Large civic water reservoirs and luxury garden pavilions | Low; captures wind from all directions including dust |
Practical Constraints
Every successful decoration project must account for physical and environmental constraints:
Fine airborne dust infiltration during desert shamal storms.
High-velocity winds carry fine particulate dust that settles across indoor carpets and furniture. Mitigation: Incorporate internal textile dampers or wooden hatch doors (darcheh) at room outlets to throttle shafts during storms.
Wind shear vibration on 30-meter free-standing baffle walls.
Buffeting desert gales can cause thin unreinforced brick baffles to vibrate and crack. Mitigation: Interlock baffles with horizontal timber tie-plates and bond them into outer wall pockets every 2 meters.
Execution Blueprint & Craftsmanship Sequence
Execute this professional sequence to achieve flawless results without backtracking:
Centerline Grid Layout
Snap reference chalk axes across the top of the foundation slab, laying out the intersection of internal baffle walls.
Perimeter Brick Pier Construction
Erect the four corner structural piers from dense kiln-fired bricks to carry wind loads and intake roof dead-weight.
Cross-Baffle (Pareh) Masonry
Lay thin 10 cm brick partitions diagonally between corner piers, bonding joints with quick-setting gach (gypsum) mortar.
Aperture Constriction Detailing
Narrow the intake throat at the top of each flue using corbelled brickwork to accelerate incoming air velocities.
Angled Timber Louver Fitting
Install downward-angled cypress or walnut louver slats within intake archways to exclude rain and birds.
Internal Flue Gypsum Smoothing
Trowel smooth white gach plaster down the interior faces of all flues to eliminate air friction and turbulence.
Dust-Settling Basin Alignment
Align the bottom outlet of the descending flues directly over a sunken water basin or dust-settling gravel trap.
Airflow Velocity and Static Pressure Testing
Perform smoke tracer tests at intake ports to verify smooth laminar descent and rapid leeward suction.
Common Mistakes & Countermeasures
Avoid these costly errors that compromise aesthetics, ergonomics, and budget:
Leaving rough, unplastered brickwork inside the vertical air flues.
Failing to seal joints where internal baffles meet outer walls.
Project Execution Checklist
Track your physical progress. Checkboxes persist automatically on this device:
Frequently Asked Questions
Can the airflow through a windcatcher be shut off in winter?
Yes. Every bâdgir shaft terminates inside the home with a decorative wooden door or sliding hatch (darcheh). During freezing winter months, homeowners close and lock these hatches, completely sealing the tower to keep heat inside.
Why do some windcatchers have eight sides while others have only four?
Four-sided towers are tailored for residential homes where wind blows predominantly from one of two quadrants. Eight-sided towers are used on large communal civic structures (like water reservoirs) situated in open plazas to catch light winds from any direction.
How much does the internal baffle thickness matter?
Baffles are built as thin as possible (typically 10 to 12 cm) using lightweight bricks to maximize the cross-sectional area of the air flues while minimizing dead-weight on the building's basement vaults.
Does the windcatcher make noise when the wind blows hard?
Because the air flues are carefully proportioned with rounded aerodynamic throats, wind travels down the shaft with a gentle, muffled whoosh rather than whistling or rattling, creating a soothing ambient soundscape.
