green home design – the building envelope 2 green home construction – the building envelope 2
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Green Home Design – The Building EnvelopeGreen Home Design – The Building Envelope2 Green Home Construction– The Building EnvelopeGreen Home Construction– The Building Envelope2
The Building Envelope
• Envelope separates the indoors from outdoors.
• Envelope divides conditioned from unconditioned space.
• Examination is important because:– A sealed building
envelope is crucial to energy efficiency.
– Air leakage hurts energy efficiency.
– Construction requires a large quantity of materials.
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Building Envelope Components
Below-grade systems: foundation walls, floor slabs, basement, crawlspace
Exterior walls: Structural and nonstructural
Roof
Fenestration systems: windows and doors
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Below-Grade Systems
Functions• Provides structure
support for the framing and exterior walls
• Provides space for distribution systems (water, sewer, ducts, wiring, gas supply)
• Provides space for a washer, dryer, furnace, and water heater.
• A finished basement can provide living space.
Challenges• Waterproofing, moisture
control, and drainage • Controlling air infiltration
where the foundation connects to the exterior walls and façade
• Insulation for the main floor above
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Radon—Passive System• Clean gravel or aggregate
lager under the slab or flooring system
• Polyethylene sheeting on top of the gravel layer
• Gas-venting pipe from the gravel level through the house to the roof
• Sealed and caulked foundation
Image: www.epa.gov
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Radon Zones
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Advanced Framing
• Reduces materials used
• Increases space for insulation
• Techniques:– wider spacing
between studs– single top plates– precise cuts reducing
materials and waste28
Prefab Modular
• Significant improvement over the past few decades.
• Green modular construction:– Offers quality assurance
and systemization– Reduces materials– Produces a durable, energy-
efficient building envelope
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Structural Insulated Panels• SIPs consist of a layer of
foam sandwiched between two layers of oriented strand board (OSB).
• SIPs use strong material for structural framing, insulation, and exterior sheathing.
• Using SIPs reduce the sawn lumber requirements.
• SIPs create an air-tight, energy-efficient building envelope.
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Insulated Concrete Forms• ICFs combine cement
with polystyrene foam and sometimes bonded wood fiber.
• Can be used in both structural and below-grade construction.
• ICF construction = low-waste building shellhigh insulation and superior wind, seismic, and exterior noise resistance.
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More Choices
• Engineered wood• Wood/plastic
composite lumber• Pre-printed
sheathing and gypsum board
• Cladding from recycled paper
• Straw bale construction
• Soil-Based Materials
• Strawboard panels
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Insulation Issues
• R- Value (resistance to heat transfer)
• Affected by:– Type, installation and
density– Gaps and shrinkage–Moisture– Thermal bridging
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Recycled Material Insulation
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Insulation by Zip Code• DOE provides an online
Zip-Code Insulation Program for recommended R-values.
• Homeowners can learn where and how much to insulate based on climate and type of HVAC.
• View the calculator and learn more at
www.ornl.gov/~roofs/Zip/ZipHome.html
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Passive House• Produces a super-insulated and airtight
building envelope• Walls up to 15 inches thick and triple-
glazed windows• No conventional central heating system• 1 BTU per sq ft per heating degree day,
vs. 5–15 BTUs• Overall energy savings up to 90 percent• Best-use in colder climates
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Windows• Southern exposure
produces most light and heat.
• Green construction calls for low-emissivity (low-e) windows.
• In hot climates, the low-e coating should be on the outside.
• For cold climates, the low-e coating should be to the inside pane.
CR: Ability to resist condensation. The high the number,
the more resistant.
U-Factor: Rate of heat loss The lower
the better
VT: How much light comes through. The higher the number
the more light transmitted.
SHGC: measures how well the product blocks heat from the sun. The lower the number, the less heat transmitted.
AL: indicates potential air leakage. The lower the number, the less air leakage through
cracks in the window assembly.
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Doors
• Energy efficiency of doors and skylights are rated on same scale as windows.
• Doors lose/gain heat through direct conduction and air leakage.
• Glass sliding doors are probably the least energy-efficient.
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Cool Roofs
• A layer of material with a reflective surface is installed in the attic.
• Radiant barriers typically result in a 2 to 10 percent reduction in cooling costs.
• Is measured by solar reflectance and thermal emittance.
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Green Roofs• Check building
codes• Test the structural
capacity for extra weight
• Plan access to the roof
• Design irrigation and drainage systems
• Select plants and growing media
Rain or sprinkler
Growing medium
Root barrier
Drain core
Insulation
Roof
membraneStructural support
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Solar Roof
Solar roof technologySolar panel retrofit Solar shingle installation
Photos National Renewable Energy Lab, www.nrel.gov
• Solar roofs capture the sun’s thermal energy and convert it into electricity to power the home and heat water.
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What Do You Need to Know?
• Design choices for environmental and indoor air quality, and energy efficiency
• Efforts of builders and homeowners to integrate green systems and feature into homes
• Systems and green features and understanding of the functions
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