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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