Green Home Design – The Building Envelope 2 Green Home Construction – The Building Envelope 2

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. 24

Building Envelope Components Below-grade systems: foundation walls, floor slabs, basement, crawlspace Exterior walls: Structural and nonstructural Roof Fenestration systems: windows and doors 25

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 25

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: 26

Radon Zones 27

Advanced Framing Reduces materials used Increases space for insulation Techniques: – wider spacing between studs – single top plates – precise cuts reducing materials and waste 28

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 29

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. 30

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. 30

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 30

Insulation Issues R- Value (resistance to heat transfer) Affected by: – Type, installation and density – Gaps and shrinkage – Moisture – Thermal bridging 31

Recycled Material Insulation Denim insulation from recycled blue jeans Blown-in cellulose from recycled newspapers Icynene® foam insulation is made from the oil of the castor plant Aerogel produced from silica, sometimes called frozen smoke 32

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 33

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 34

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. 35

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. 35

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. 37

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 membrane Structural support 38

Solar Roof Solar roof technology Solar panel retrofitSolar shingle installation Photos National Renewable Energy Lab, Solar roofs capture the sun’s thermal energy and convert it into electricity to power the home and heat water. 39

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 39