# Solar Shading Design ## Table of Contents - [[#Overview]] - [[#Solar Geometry Review]] - [[#Shading Device Types]] - [[#Horizontal Overhangs]] - [[#Vertical Fins]] - [[#Egg-Crate Devices]] - [[#Brise-Soleil]] - [[#Louvers and Adjustable Systems]] - [[#Shading Coefficient and Solar Factors]] - [[#Shadow Angle Protractor]] - [[#Sizing by Orientation]] - [[#Internal vs External Shading]] - [[#Material and Detailing Considerations]] - [[#Simulation and Verification]] - [[#Key References and Standards]] --- ## Overview Solar shading is among the most consequential architectural decisions affecting energy performance, visual comfort, and facade composition. Effective shading can reduce cooling loads by 30-50%, eliminate glare, and define the architectural character of a building. Conversely, poorly designed or absent shading leads to overheating, excessive energy consumption, and occupant discomfort. Shading design must be integrated with [[Passive Solar Design]] (where winter solar admission is required), [[Daylighting Fundamentals]] (where daylight must penetrate despite shading), and [[Glare Control Methods]] (where visual comfort demands specific illuminance limits). --- ## Solar Geometry Review Shading design begins with solar geometry. The sun's position at any time is defined by: - **Altitude angle (alpha)** -- elevation above the horizon (0 deg at horizon, 90 deg at zenith) - **Azimuth angle (phi)** -- horizontal angle measured clockwise from north (or from south in some conventions) - **Profile angle (gamma)** -- the angle in the vertical plane perpendicular to the facade; this is the angle used to size horizontal shading devices **Profile angle formula:** tan(gamma) = tan(alpha) / cos(surface-solar azimuth) Where surface-solar azimuth is the difference between the sun's azimuth and the wall's azimuth (its orientation). ### Sun Path Diagrams Stereographic or equidistant sun path diagrams plot the sun's position throughout the year for a given latitude. These are essential tools for: - Identifying critical shading periods - Reading off altitude and azimuth for any hour and date - Overlaying shading masks to verify device performance --- ## Shading Device Types ### Classification by Geometry | Type | Primary Effectiveness | Best Orientation | |------|----------------------|-----------------| | Horizontal overhang | High-altitude sun | South (N. hemisphere), near equator | | Vertical fins | Low-altitude, oblique sun | East and West | | Egg-crate (combined) | Multi-angle sun | East, West, and near-equatorial South | | Diagonal / angled | Specific azimuth ranges | Any, custom designed | ### Classification by Operation - **Fixed** -- permanent elements, no maintenance, limited adaptability - **Adjustable / operable** -- louvers, blinds, sliding screens; respond to varying conditions - **Retractable** -- awnings, roller shutters; fully removed when shading not needed - **Responsive** -- automated systems driven by sensors or building management systems --- ## Horizontal Overhangs The most fundamental shading device, effective on south-facing facades (northern hemisphere) where the sun is high. ### Sizing Principle An overhang must cast a shadow to the window sill at the design cut-off date/time. **Overhang depth (D) = Window height (H) / tan(profile angle at cut-off)** ### Example Calculation For a south-facing window at latitude 35 deg N: - Window height: 1.8 m (sill to overhang) - Design profile angle at summer solstice noon: 78.5 deg - Design profile angle at equinox noon: 55 deg To shade the full window at equinox noon: D = 1.8 / tan(55 deg) = 1.8 / 1.428 = 1.26 m ### Practical Considerations - Overhangs can be solid (slab extension) or open (pergola, louvres) -- open overhangs maintain sky view for diffuse daylight - Gap between overhang and window head allows hot air to escape rather than being trapped - Combined horizontal overhang with light shelf redirects daylight deeper into the room - Overhang depth beyond **1.5 m** may require structural consideration and weather detailing --- ## Vertical Fins Vertical fins block low-altitude sun arriving from oblique angles. They are the primary device for east and west facades where the sun is low and horizontal overhang effectiveness is limited. ### Design Parameters - **Projection depth** -- determines the angular range of sun blocked - **Spacing** -- closer spacing blocks more sun but also reduces view and daylight - **Angle/rotation** -- fins angled toward the equator block more afternoon sun (west) or morning sun (east) while maintaining some view ### Horizontal Shadow Angle (HSA) The horizontal shadow angle defines the cut-off angle in plan view: **tan(HSA) = fin depth / fin spacing** For HSA = 45 deg: fin depth = fin spacing For HSA = 60 deg: fin depth = 1.73 x fin spacing ### Practical Notes - Angled fins (rotated 15-30 deg from perpendicular) are more effective than orthogonal fins for east/west facades - Operable vertical louvers allow occupant control - Fins also function as wind scoops for ventilation when appropriately oriented --- ## Egg-Crate Devices Egg-crate shading combines horizontal and vertical elements in a grid. This configuration blocks sun from multiple angles and is particularly effective on: - East and west facades in tropical latitudes - South-facing facades near the equator where the sun passes overhead - Facades receiving sun from widely varying azimuth angles ### Design The egg-crate is characterised by two parameters: - **Vertical shadow angle (VSA)** -- governed by horizontal element depth - **Horizontal shadow angle (HSA)** -- governed by vertical element depth A shading mask for an egg-crate device appears as a combination of the horizontal and vertical masks -- a segmented area on the sun path diagram. ### Advantages and Limitations - Excellent solar control across a wide range of angles - Significant visual impact on facade composition - Reduces view and daylight transmission substantially - Higher cost and maintenance than simple overhangs - Requires careful coordination with fire safety (facade access, compartmentation) --- ## Brise-Soleil The brise-soleil ("sun breaker"), popularised by Le Corbusier, is an architectural-scale shading system typically comprising deep horizontal or vertical blades, often in reinforced concrete, standing off from the glazing plane. ### Design Principles - Creates a secondary facade layer, shading the primary glazing - Provides depth and articulation to the building elevation - Can incorporate maintenance walkways and service access - Blade angle and spacing designed using shadow angle protractor ### Notable Examples - **Unite d'Habitation, Marseille** (Le Corbusier, 1952) -- deep concrete brise-soleil as primary facade expression - **Ministry of Education and Health, Rio de Janeiro** (Costa, Niemeyer et al., 1943) -- adjustable horizontal louvers on north facade - **Chandigarh Secretariat** (Le Corbusier, 1953) -- massive concrete brise-soleil responding to Indian climate --- ## Louvers and Adjustable Systems ### Fixed Louvers - Horizontal louvers at specific blade angles act as multiple mini-overhangs - Blade angle set to the profile angle of the sun at the design cut-off date - Spaced to maintain view and daylight while blocking direct sun - Materials: aluminium, timber, steel, glass, perforated metal ### Operable Louvers - Allow seasonal and daily adjustment - Manual or automated (linked to BMS, solar sensors, or time clock) - Venetian blinds are the interior equivalent, though far less effective thermally - External operable louvers provide best performance but require robust mechanisms ### Automated Responsive Systems - Sensor-driven systems track sun position and adjust louver angle - Can respond to cloud cover, reducing unnecessary shading - Capital cost premium of 30-50% over fixed systems, offset by energy savings - Maintenance and reliability are critical design considerations --- ## Shading Coefficient and Solar Factors ### Shading Coefficient (SC) The shading coefficient is the ratio of solar heat gain through a glazing/shading combination to that through a reference single clear glass: **SC = SHGC of system / SHGC of single clear glass (0.87)** This older metric is being replaced by SHGC but still appears in many references. ### Solar Heat Gain Coefficient (SHGC) Total solar energy transmitted through the fenestration system, including shading devices: **Effective SHGC = Glazing SHGC x Shading device factor** | Shading Device | Typical Factor | |---------------|---------------| | No shading | 1.00 | | External venetian blind (45 deg) | 0.10-0.15 | | External roller blind (light colour) | 0.15-0.20 | | External fixed louvers | 0.15-0.30 | | Internal venetian blind (45 deg) | 0.45-0.55 | | Internal roller blind (light) | 0.40-0.50 | | Mid-pane blind (double glazing) | 0.25-0.35 | **Key insight:** External shading devices are **2-3 times more effective** than internal devices because they intercept solar radiation before it enters the building. --- ## Shadow Angle Protractor The shadow angle protractor (also called the shading mask protractor) is a circular overlay tool used with stereographic sun path diagrams. ### How to Use 1. Determine the **vertical shadow angle (VSA)** -- the profile angle blocked by horizontal elements 2. Determine the **horizontal shadow angle (HSA)** -- the angle blocked by vertical elements 3. Plot these angles on the protractor: - VSA produces a curved horizontal line (segmental arc) on the diagram - HSA produces radial lines from the centre 4. Overlay the protractor (oriented to the facade azimuth) on the sun path diagram 5. All sun positions falling within the shaded area of the protractor are blocked by the device ### Reading Results - Hours and months where the sun is shaded can be read directly - The percentage of occupied hours with effective shading can be quantified - Gaps in shading coverage reveal where supplementary measures are needed --- ## Sizing by Orientation ### South Facade (Northern Hemisphere) - **Horizontal overhangs** are highly effective; the sun is high in summer and low in winter - Size for equinox cut-off (21 March / 21 September) to balance winter gain and summer shading - Fixed overhangs can achieve 90-100% summer shading while admitting 70-90% of winter sun ### North Facade (Northern Hemisphere) - Receives minimal direct sun (early morning and late evening in summer only) - Shading is generally unnecessary; focus on low U-value glazing and daylight ### East Facade - Morning sun at low altitude; horizontal overhangs ineffective - **Vertical fins** or **egg-crate** devices required - Operable elements preferred (shading needed only in morning hours) - Deciduous planting can supplement architectural devices ### West Facade - The most challenging orientation: afternoon sun at low altitude coincides with peak ambient temperature - **Vertical fins** angled toward south are most effective - Operable louvers or shutters strongly recommended - Minimise west-facing glazing area wherever possible - West facades require the most aggressive shading specification --- ## Internal vs External Shading | Criterion | External Shading | Internal Shading | |-----------|-----------------|-----------------| | Solar gain reduction | 70-90% | 30-55% | | Glare control | Excellent | Good | | View preservation | Variable (device-dependent) | Good (adjustable) | | Maintenance access | Requires facade access | Easy | | Wind/weather resistance | Must be designed for local conditions | Not applicable | | Cost | Higher initial cost | Lower initial cost | | Occupant control | Limited (unless automated) | Immediate | **Design recommendation:** Always prioritise external shading for solar gain control. Use internal devices as supplementary glare control. --- ## Material and Detailing Considerations - **Aluminium** -- lightweight, durable, low maintenance; specify with thermal break if connected to facade - **Timber** -- natural appearance, lower embodied carbon; requires maintenance, suitable for sheltered locations - **Steel** -- allows slender profiles for larger spans; requires corrosion protection - **Concrete** -- integral with structure, high thermal mass (can re-radiate stored heat); heavy, permanent - **Perforated metal** -- reduces wind load, maintains some transparency, provides dappled light effect - **ETFE / fabric** -- lightweight tensile shading, translucent, suitable for large spans - **Glass fins / louvres** -- maintain transparency, high aesthetic quality, significant cost ### Detailing Principles - Ensure drainage path for rainwater captured by horizontal elements - Provide adequate fixing to resist wind loads (calculate wind pressure on projected area) - Maintain window cleaning and facade access - Coordinate with fire compartmentation requirements - Consider bird nesting prevention in louver assemblies --- ## Simulation and Verification | Tool | Application | |------|-------------| | Sun path diagram + protractor | Manual verification, preliminary sizing | | SketchUp + shadow analysis | Quick 3D shadow studies, client presentation | | Ladybug (Grasshopper) | Radiation analysis, shading studies | | IES VE SunCast | Detailed shadow mapping on building surfaces | | Radiance/DAYSIM | Accurate daylight simulation with shading | | EnergyPlus | Energy impact of shading strategies | --- ## Key References and Standards - Olgyay, A. and Olgyay, V. (1957). *Solar Control and Shading Devices* - Lechner, N. (2014). *Heating, Cooling, Lighting* - CIBSE Guide A -- Solar gain calculations and shading factors - ASHRAE Handbook -- Fundamentals, Chapter 15: Fenestration - EN 13363 -- Solar protection devices combined with glazing - BS 8206-2 -- Lighting for buildings, daylighting (shading interaction) --- #environment #shading