Slab

Double Stud Wall / Slab on Grade w/Stem Wall

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How to Build Efficiently in Massachusetts

Plans call for a slab-on-grade foundation with radiant heat and double-stud walls. Comments?

Posted on Sep 26 2011 by Scott Gibson

Noah Kaput and his wife seem to be off to a good start in planning their 2,100-sq. ft. house in Massachusetts.


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Image Credits:

  1. Fine Homebuilding

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How to Insulate a Slab Foundation—With Straw-Bales?

Can straw bales be used as horizontal insulation under a concrete slab?

Posted on Feb 7 2011 by Scott Gibson

Superinsulated houses need insulation under the slab as well as in the walls and roof, and the most common choice for sub-slab insulation is rigid foam.


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Image Credits:

  1. Lucas Durand

Building Plans for the Energy Star Thermal Bypass Checklist

How to Build an Energy Star Home: Construction Details That Help You to Build Tight Houses — The First Time

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Deep Energy Retrofit: Focus on the Envelope

You can't expect to cut a home's energy use by 50% without a serious renovation of its exterior envelope. For all its components—walls, roof, foundation, slab—the details need to be worked out.

Posted on Jul 20 2010 by Christopher Briley

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This is part two of the Green Architects' Lounge three-part series on deep energy retrofits.

In this episode, Phil and I discuss what we believe is the most crucial part of a DER: the exterior building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials..

There is no single solution. Here, we must be nimble and thoughtful, and deal with the structure that we're given and apply the skills we've learned (and by we, I mean all of you listeners as well).


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Image Credits:

  1. Photo by Jesse Thopson (amateur photographer, professional architect)

Do I Have to be A Building Scientist To Build Green?

Knowing something about building science helps, yes.

Builders who are just starting to dive into green building will need a grasp of basic techniques: how to make sure the building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. is tight, the pitfalls of sloppy HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. installations, how much insulation to install and which types work best, how to install windows and doors so they don’t leak, what kind of roofing is appropriate for the climate.

Slab Foundations

UPDATED 11/15/2012

Slab-on-Grade Foundations Work Everywhere

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Image Credits:

  1. Charles Lockhart
  2. Daniel S. Morrison/Fine Homebuilding #160
  3. Brian Pontolilo/Fine Homebuilding #178
  4. Paddy Morrissey, Code Check Building 2nd Edition
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Super Energy-Efficient Home in Vermont

Waitsfield, VT

Oct 10 2008 By Rob Wotzak | 19 comments

General Specs and Team

Location: Waitsfield, VT
Bedrooms: 3
Bathrooms: 2
Living Space : 2000 sqf
Cost (USD/sq. ft.): $90/sqf

Builder: Al Rossetto, A. Rosetto Construction
Architect/designer: Al Rossetto

Construction

Foundation: shallow frost-protected footing, gravel in perforated PVC forms/drains, 2 in. XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. (R-10) buried and extending horizontally distance of frost depth; 6-in. ICFInsulated concrete form. Hollow insulated forms, usually made from expanded polystyrene (EPS), used for building walls (foundation and above-ground); after stacking and stabilizing the forms, the aligned cores are filled with concrete, which provides the wall structure. walls (Amvic, R-22)
Walls: 6.5-in. SIPs (Insulspan, R-22)
Roof:12.25-in. SIPs (Insulspan, R-50)
Windows: triple-pane, low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor., argonInert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows. -filled; SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1., .24, U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. , .2 (Kohltech, R-5)
Garage:none

Energy

Heating/cooling: radiant heating system fed by solar and gas hot-water heater, 4 flat-plate solar collectors with 120-gallon storage tank and solar heat exchangerDevice that transfers heat from one material or medium to another. An air-to-air heat exchanger, or heat-recovery ventilator, transfers heat from one airstream to another. A copper-pipe heat exchanger in a solar water-heater tank transfers heat from the heat-transfer fluid circulating through a solar collector to the potable water in the storage tank.
Water heating: shared with radiant heating system
HERSIndex or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a Home Energy Rating System (HERS) Reference Home based on the 2006 International Energy Conservation Code. A home matching the reference home has a HERS Index of 100. The lower a home’s HERS Index, the more energy efficient it is. A typical existing home has a HERS Index of 130; a net zero energy home has a HERS Index of 0. Older versions of the HERS index were based on a scale that was largely just the opposite in structure--a HERS rating of 100 represented a net zero energy home, while the reference home had a score of 80. There are issues that complicate converting old to new or new to old scores, but the basic formula is: New HERS index = (100 - Old HERS score) * 5. score: 95.3 (old system)
Annual energy use: 51.4 MMBtu

  • Concrete slab over 16-in. sand bed for significant thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night.
  • Extremely tight building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials.
  • Solar hot water and radiant heat
  • DaylightingUse of sunlight for daytime lighting needs. Daylighting strategies include solar orientation of windows as well as the use of skylights, clerestory windows, solar tubes, reflective surfaces, and interior glazing to allow light to move through a structure. facilitated by open floor plan and window layout
  • All lighting is CFLCompact fluorescent lamp. Fluorescent lightbulb in which the tube is folded or twisted into a spiral to concentrate the light output. CFLs are typically three to four times as efficient as incandescent lightbulbs, and last eight to ten times as long. CFLs combine the efficiency of fluorescent light with the convenience of an Edison or screw-in base, and new types have been developed that better mimic the light quality of incandescents. Not all CFLs can be dimmed, and frequent on-off cycling can shorten their life. Concerns have been raised over the mercury content of CFLs, and though they have been deemed safe, proper recycling and disposal is encouraged. or LEDLight-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed.

Indoor Air Quality

  • Interior portion of Form-A-Drain footing system (under slab) is part of a natural-draft radonColorless, odorless, short-lived radioactive gas that can seep into homes and result in lung cancer risk. Radon and its decay products emit cancer-causing alpha, beta, and gamma particles.-venting system
  • ERV(ERV). The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV.
  • Solid wood cabinets and flooring
  • Central vacuum system

Green Materials and Resource Efficiency

  • Fiber-cement siding
  • Trees cut down on site milled into stair parts and loft flooring
  • Almost all construction waste recycled

Certification

EnergyStar score: 5+ stars

Modest House Built to Scandinavian Green Standards

This modest home may not seem out of the ordinary, but energy efficiency specialist Efficiency Vermont calls it extraordinary — "Best of the Best" and "the most energy efficient home in the state," to be specific. With a HERSIndex or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a Home Energy Rating System (HERS) Reference Home based on the 2006 International Energy Conservation Code. A home matching the reference home has a HERS Index of 100. The lower a home’s HERS Index, the more energy efficient it is. A typical existing home has a HERS Index of 130; a net zero energy home has a HERS Index of 0. Older versions of the HERS index were based on a scale that was largely just the opposite in structure--a HERS rating of 100 represented a net zero energy home, while the reference home had a score of 80. There are issues that complicate converting old to new or new to old scores, but the basic formula is: New HERS index = (100 - Old HERS score) * 5. score of 95.3 out of 100, and four years of energy bills to document its performance, the building deserves the accolades. Builder Al Rossetto leaves nothing to chance: he has used the same construction details to lock in five-star Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. ratings for every home he has built since.

Lessons Learned

Don't let all the fancy acronyms scare you. Green building isn't only about using exotic materials and high-tech HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. components. Building an energy efficient home is often just a matter of doing a good job. The SIPs came with an installation manual. "We read it, followed the directions and were conscientious during our work," Al explained. Paying attention to details by filling voids and cracks with spray foam and caulk isn't hard work, but it can make all the difference when it's time to turn on the heat.


Rob Wotzak is assistant editor at GreenBuildingAdvisor.com

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Image Credits:

  1. Chris Green/Fine Homebuilding 161
  2. Rob Wotzak

Insulate the perimeter of all concrete slabs

Before pouring a concrete slab, install rigid foam insulation along its perimeter.
If the slab isn't isolated by foam, there will be a thermal bridge to the foundation or soil. This makes the edge of the slab cold, compromising energy efficiency and possibly raising the temperature of the slab perimeter above the due point. This could cause condensation and mold growth. The insulation should separate the slab perimeter from all exterior foundation walls, footings, or soil.

Insulate beneath concrete slabs regardless of climate

Use 2-in. of XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. (R-10) in all but the warmest climates
When detailing a concrete slab on grade, add insulation at the perimeter and beneath the slab. This is useful even in warm, humid climates. Here, insulation beneath the slab isolates the living space from cool below-grade temperatures. This reduces the chance that warm, humid air will condense on cool concrete floors. In Florida and the southern-most parts of Texas, Louisiana, Alabama, and Georgia you could drop back to 1-in. or R-5.

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