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 Mobile ViewSOLAR ENERGY SYSTEMS AIR CONDITIONING & HEAT PUMP SYSTEMS AIR BYPASS LEAKS AIR LEAK DETECTION TOOLS AIR LEAK MINIMIZATION AIR POLLUTANTS, COMMON INDOOR AIR LEAK SEALING PROCEDURE AIR SEALING STRATEGIES BIOGAS PRODUCTION & USE ENERGY SAVINGS in BUILDINGS EVAPORATIVE COOLING SYSTEMS FLOOR, CERAMIC TILE FLOOR, CONCRETE SLAB CHOICES FLOOR, CONCRETE SLAB POURED FINISH FLOOR DAMAGE DIAGNOSIS FLOOR, ENGINEERED WOOD & LAMINATES FLOOR FRAMING & SUBFLOOR for TILE FLOOR, KITCHEN & BATH OPTIONS FLOOR, LAMINATE PLASTIC FLOOR RADIANT HEAT Mistakes to Avoid FLOOR, RESILIENT VINYL or CORK FLOOR, STONE, GRANITE, MARBLE, AGGLOMER FLOOR & SUBFLOOR MOLD, HIDDEN FLOOR TYPES & DEFECTS FOOTING & FOUNDATION DRAINS FOOTINGS EXPOSED, Repair Methods FOUNDATION CRACKS & DAMAGE GUIDE FRAMING DETAILS for BETTER INSULATION FRAMING DETAILS for DOUBLE WALL HOUSES FRAMING METAL STUD PERFORMANCE FREEZE-PROOF A BUILDING FROST HEAVES, FOUNDATION, SLAB GREEN BUILDING CONSTRUCTION CODES GUIDES GREENHOUSE DESIGN for SOLAR HEATING GREENHOUSE / SUNSPACE GLARE HEAT LOSS in BUILDINGS HEAT LOSS DETECTION TOOLS HEAT LOSS INDICATORS HEAT LOSS PREVENTION PRIORITIES HEAT LOSS R U & K VALUE CALCULATION HEAT LOSS RATE CALCULATIONS HEATING SMALL LOADS HEATING SYSTEMS HOUSEWRAP INSTALLATION DETAILS HUMIDITY LEVEL TARGET ICE DAM PREVENTION INDOOR AIR QUALITY & HOUSE TIGHTNESS INSULATION IDENTIFICATION GUIDE INSULATION INSPECTION & IMPROVEMENT INSULATION LOCATION - WHERE TO PUT IT LEED GREEN BUILDING CERTIFICATION LEED Building Designation & IAQ MOISTURE CONTROL in BUILDINGS Nanomaterials Hazards NOISE / SOUND DIAGNOSIS & CURE ODORS & SMELLS DIAGNOSIS & CURE PLUMBING SYSTEM INSPECT DIAGNOSE REPAIR RADIANT SLAB FLOORING CHOICES RADIANT SLAB TUBING & FLUID CHOICES ROOFING INSPECTION & REPAIR ROOF VENTILATION SPECIFICATIONS SHEATHING, FOIL FACED - VENTS SOLAR ENERGY SYSTEMS BLOCKBED RADIANT FLOORS - SOLAR DESIGN FLOOR, CONCRETE SLAB CHOICES FLOOR, CONCRETE SLAB POURED FINISH GLASS vs HEAT MIRROR SOLAR GAIN/Loss GREENHOUSE DESIGN for SOLAR HEATING GREENHOUSE / SUNSPACE GLARE PASSIVE SOLAR DESIGN HANDBOOK - PDF PASSIVE SOLAR DESIGN KEY ELEMENTS Passive Solar Basics Passive Solar 5 Design Elements - Aperture - Absorber - Thermal mass - Distribution - Control How Passive Solar Works - Conduction - Convection - Radiation - Thermal capacitance Direct Solar Gain Indirect Solar Gain - Trombe Walls Isolated Solar Gain Roof & Window Overhangs Roof Overhangs Control Solar Gain - Types of Overhangs - Sizing Roof Overhangs - Overhangs Ordinances PASSIVE SOLAR DESIGN METHOD PASSIVE SOLAR ENERGY MONITORING PASSIVE SOLAR FLOOR TILES, PHASE CHANGE PASSIVE SOLAR HEAT PERFORMANCE PASSIVE SOLAR HOME, LOW COST PASSIVE SOLAR PERFORMANCE PROBE PASSIVE SOLAR Roof & Window Overhangs PHOTOVOLTAIC POWER SYSTEMS POLYCARBONATE GLAZING REMOTE ELECTRIC POWER, PHOTOVOLTAIC ROCK-BED SOLAR HEAT STORAGE DESIGN SLAB INSULATION, PASSIVE SOLAR SLATE THERMAL MASS for SOLAR HEAT STORAGE SOLAR COLLECTOR AIR or GAS COLLECTION SOLAR COLLECTOR EFFICIENCY COMPARISONS SOLAR COLLECTOR FILMS SOLAR COLLECTOR OUTGASSING SOLAR COLLECTOR WOOD HOUSINGS SOLAR GAIN CALCULATION SOLAR HEATING SYSTEM DESIGNS SOLAR HOT WATER HEATERS SOLAR HOUSE EVALUATION SOLAR MODULE MANUFACTURERS SOLAR SHADES & SUNSCREENS SOLAR SHADES, LOW-E EFFECTIVENESS SOLAR WATER DISINFECTION SOLAR HOT WATER HEATERS SUNSPACE DESIGN for SOLAR HEATING SUNSPACE GLAZING for SUNTANNING STORM WINDOW INTERIOR STORM WINDOW PLASTIC CHOICES STORM WINDOW WEEP HOLES SUNGAIN, FILMS, LOW-E GLASS SUNSPACE GLAZING for SUNTANNING SWIMMING POOL SOLAR HEAT, INDOOR SWIMMING POOL SOLAR HEAT, OUTDOOR DIAGNOSIS THERMAL MASS in BUILDINGS STRUCTURAL INSPECTIONS & DEFECTS SUMP PUMPS GUIDE SWEATING (CONDENSATION) on PIPES, TANKS THERMAL EXPANSION of MATERIALS THERMAL MASS in buildings THERMAL MASS FLOOR SLABS THERMAL MASS in UPSTAIRS THERMAL MASS WALL DESIGN THERMAL MASS in HOMES - STUDY THERMAL MASS TRADEOFFS, HEATING vs COOLING THERMAL TRACKING & HEAT LOSS VAPOR BARRIERS & AIR SEALING at BAND JOISTS VAPOR BARRIERS & CONDENSATION in BUILDINGS VAPOR BARRIERS & HOUSEWRAP VAPOR CONDENSATION & BUILDING SHEATHING VENTILATION in BUILDINGS WATER HEATERS WATER SOFTENERS & CONDITIONERS WIND ENERGY SYSTEMS WIND TURBINES & LIGHTNING WINDOWS & DOORS WINTERIZE A BUILDING WOOD Burning Heaters Fireplaces Stoves More Information |
Use of roof overhangs & shading to control heat gain in buildings: This article discusses the use of roof overhangs as a component of passive solar design; we include links to additional passive solar design as well as solar design evaluation questions and answers. InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers nor with topics or services discussed at this website.Readers who have not already done so should start reading at PASSIVE SOLAR DESIGN KEY ELEMENTS. Readers wanting more detail about passive solar design should see SOLAR ENERGY SYSTEMS. Our page top photo illustrates extensive use of solar shading on a government office building in Queretaro, Mexico. Readers should also see an alternative or supplement to controlling solar gains with a roof or window overhang (this article): the use of SOLAR SHADES & SUNSCREENS. © Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website. Passive Solar Home Design - Roof OverhangsPassive Solar Home Design for Summer Comfort - using shade
Roof Overhangs Control Building Heat Gain & SunlightThe physical dimensions of an overhang are an important element because overheating will occur unless the overhang provides enough shade. [The solar overhang shown in our photo (above-left) is located on a home in San Miguel de Allende, Mexico and is discussed in more detail at PASSIVE SOLAR HEAT PERFORMANCE. The addition of these small overhangs above windows on the East and West facing sides of this studio made the difference between having a comfortable space and having a space that was just too warm to occupy late in the afternoons. For a contrasting example, another home in the same area that has no roof overhangs to control solar gain is discussed at PASSIVE SOLAR HOME, LOW COST. -- DF] Many variables—including latitude, climate, solar radiation transmittance, il luminance levels, and window size and type—need to be considered for properly sizing an overhang in a specific locale. Therefore, it's best to have an experienced solar designer or builder calculate the proper overhang dimensions. For more information, see roof overhangs [below] for shading building elements. In passive solar home design, exterior roof overhangs provide a practical method for shading building elements such as windows, doors, and walls. How Roof Overhangs or Other Window Overhangs Work to Control Heat and Solar GainOverhangs are most effective for south facing elements (in the northern hemisphere) and at midday. If the building element bears more than about 30° off true south, the effectiveness of an overhang, as with any solar feature, begins to decrease significantly. Overhangs usually only affect the amount of direct solar radiation that strikes a surface. Diffuse sky and reflected radiation gains are not often directly affected by overhangs. The higher overhead the sun is, the shorter the shadow a person will cast on the ground. However, the short brim of a baseball cap can create a long shadow across the body of a standing person. The same concept applies in designing overhangs for buildings. The higher, or more vertical, the arc of the sun, the longer the shadow that the building overhang generates along the face of the wall. Summer shadows extend down walls the furthest, winter shadows the least. Sites closer to the equatorial path of the sun have deeper-extending wall shadows than ones farther from the equator, assuming the same overhang length. Types of Roof or Window Overhangs for Sunlight & Solar Gain Control
Our photo (left) demonstrates a passive solar overhang in use on the East-facing wall of this building on the Vassar College campus, Poughkeepsie, NY. Overhangs may also be fixed, operable, and/or removable. Examples include roof eaves, awnings, and Bahama shutters (top-hinged louvered shutters typically propped open with wooden dowels) respectively. Fixed overhangs offer perceived longevity and low maintenance at the expense of flexibility or the ability to adjust to site-specific factors. Although adjustable devices allow the user to fine tune the amount of shade or direct sunlight, they require more maintenance. Removable fixtures generally provide flexibility and longevity plus some personal involvement with installation and removal.
While northern-hemisphere shading may be welcome in September because of the heat, shading in March may be undesirable. Vegetation, on the other hand, can follow the climatic seasons. Vines that shed their leaves for winter usually leaf out about the time shading is needed. Movable shading devices, while adjustable, often become maintenance problems. Sizing Roof or Window OverhangsUnfortunately, there is as yet no universally simple formula for sizing overhangs. While one overhang methodology works well for some locations, it can be completely inappropriate for others. For example, there are a limited number of overhang-sizing guidelines acceptable for buildings located in southern states, particularly hot-humid climates. Guidelines acceptable for the high plains of Montana are unlikely to work for a site in Florida. Due to the varying microclimate conditions encountered across the United States, the methods presented here are general in scope. Anyone seeking a more specialized analysis should seek professional advice from an architect trained in passive solar design. Every climate requires special design attention. The following general guidelines may be useful in determining a suitable overhang design. The guidelines are listed by climate type, for solar noon, when the sun reaches its maximum altitude for a given day. Solar noon is very rarely the same as noon in local standard time.
*(HDD and CDD data is available from local weather services.) Roof or Window Solar Gain Control Overhangs and Zoning OrdinancesOverhangs may be inappropriate for sites with restrictive regulatory guidelines. For example, your calculations indicate your house needs a three foot (~1 meter[m]) overhang on the front. The local zoning ordinance restricts eave extension to two feet (0.61 m) beyond the front yard setback. If your house will be or is located precisely on the setback, you must do one of the following:
List of Passive Solar Design Key Reference Books including Online TextsThe first three passive solar design handbook links below are to free, online documents.
Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. Questions & Answers regarding this articleQuestions & answers about the use of roof overhangs & shading to control heat gain in buildings. Ask a Question or Search InspectAPediaHTML Comment Box is loading comments...
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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website. PASSIVE SOLAR DESIGN HANDBOOK - PDF
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Openings, such as windows, do not always require fixed overhangs. A fixed overhang designed for optimal shading on the autumnal equinox (September 21) casts the same shadow on the vernal equinox (March 21). 
