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ACOUSTICAL SEALANT CHOICES
AIR LEAK MINIMIZATION
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BASEMENT CEILING VAPOR BARRIER
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BLOWN-IN INSULATION
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FRAMING DETAILS for BETTER INSULATION
FRAMING DETAILS for DOUBLE WALL HOUSES
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HEAT LOSS in BUILDINGS
HEAT LOSS PREVENTION PRIORITIES
HEAT LOSS R U & K VALUE CALCULATION
HOUSEWRAP AIR & VAPOR BARRIERS
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ICE DAM PREVENTION
INSULATION AIR & HEAT LEAKS
INDOOR AIR QUALITY & HOUSE TIGHTNESS
INSULATION CHOICES
INSULATION FACT SHEET- DOE
INSULATION IDENTIFICATION GUIDE
INSULATION INSPECTION & IMPROVEMENT
INSULATION LOCATION - WHERE TO PUT IT
INSULATION MOLD
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LEED GREEN BUILDING CERTIFICATION
LOG HOME ENERGY EFFICIENCY

MOLD in FOAM INSULATION, RESISTANCE
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NOISE / SOUND DIAGNOSIS & CURE

PASCAL CALCULATIONS

RADIANT BARRIERS
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SHEATHING, FOIL FACED - VENTS
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STAINS on & in BUILDINGS, CAUSES & CURES
STRAW BALE CONSTRUCTION
STUCCO WALL METHODS & INSTALLATION
STUCCO OVER FOAM INSULATION
SWEATING (CONDENSATION) on PIPES, TANKS

Thermal Expansion Cracking of Brick
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THERMAL MASS in BUILDINGS
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VAPOR BARRIERS & CONDENSATION in BUILDINGS
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WALL CONSTRUCTION BARRIER vs CAVITY
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WINTERIZE A BUILDING


ZONE DAMPERS
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More Information

Polystyrene foam insulation (C) Daniel FriedmanFoundation Insulation Options
Guide to Underground & Aboveground Use of Polystyrene Foam Board
     

  • Foundation Insulation Options for buildings - using polystyrene
    • Insulating below grade with polystyrene foam insulation - choices
    • Performance comparison of expanded polystyrene and extruded polystyrene foam insulating panels for underground foundation insulation
    • Dow Chemical Study Reports insulating performance of extruded and expanded foam insulation used below grade after 6 and 18-month exposures
    • Recommended protective coatings for foam insulating board used against building foundations
  • Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices
  • Questions & Answers about foundation insulation choices & methods
  • References

Click to Show or Hide Related Topics

  • INSULATION IDENTIFICATION GUIDE - home
  • ASBESTOS IDENTIFICATION IN buildings
  • ASBESTOS-FREE INSULATION MATERIALS
  • ASBESTOS PIPE INSULATION
  • BALSAM WOOL BATT INSULATION
  • BLOCK WALL INSULATION RETROFIT
  • BLOWN-IN INSULATION
  • BRICK LINED WALLS
  • BRICK VENEER WALL AIR LEAKS
  • BRICK WALL INSULATION RETROFIT
  • CELLULOSE LOOSE FILL INSULATION
  • CERAMIC INSULATION
  • CONCRETE INSULATION, light-weight
  • COTTON INSULATION BATTS
  • DUST SAMPLING PROCEDURE
  • FIBERGLASS INSULATION
  • FOAM BOARD Insulation
  • FOAM INSULATION TYPES - Visual Id
  • FOAM INSULATION & INSECTS
  • HOMASOTE & OTHER INSULATING BOARDS
  • ICYNENE FOAM SPRAY INSULATION
  • MINERAL WOOL - ROCK WOOL INSULATION
  • PAPER INSULATION on DUCTS
  • PERLITE INSULATION
  • PHENOLIC FOAM INSULATION
  • POLYISOCYANURATE FOAM INSULATION
  • POLYISOCYANURATE FOAM BELOW SLABS
  • POLYSTYRENE FOAM INSULATION
  • RADIANT BARRIERS
  • REFLECTIVE INSULATION
  • RIGID FOAM USE INDOORS
  • STRESS SKIN INSULATED PANELS
  • STUCCO OVER FOAM INSULATION
  • SUPER HI-R INSULATION
  • SUPERINSULATION RETROFIT
  • UREA FORMALDEHYDE FOAM INSULATION UFFI
  • URETHANE FOAM
  • VERMICULITE INSULATION
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

This article discusses the question: which is the best foundation insulation to use below-ground. Accompanying text is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.

Underground use of Polystyrene Foam Insulating Board

  • Polystyrene Underground: Q&A on Underground Use of Polystyrene Foam Insulating Board - PDF-form; use your browser's back button to return to this page
  • Q&A: Foundation Foam Protection using Styrofoam - how to protect - original PDF form; use your browser's back button to return to this page or jump to the updated text at Foundation Foam Insulation Protection below.

The question-and-answer article about the below-grade use of expanded versus extruded polystyrene insulating foam boards, found just board, below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Is Expanded or Extruded Polystyrene Foam Insulation Better to Use for Underground Foundation Insulation?

Polystyrene foam insulation below concrete slab (C) Daniel Friedman

Question:

I am building an earth-sheltered home and discovered that I could save a great deal of money by insulating below grade with expanded rather than extruded polystyrene foam insulation. Is it unwise to use the expanded polystyrene board, given its tendency to absorb moisture below grade? -- D.S., San Jose, CA

Our photo (left) shows polystyrene foam insulating board below a concrete slab being poured in Two Harbors, MN.

Answer:

Basement heat loss (C) Daniel FriedmanWidely reported research by Dow Chemical Co. shows that their extruded polystyrene foam insulation, on average, outperforms expanded polystyrene (EPS) in below-grade insulation applications. Due to the study's limitations, however, Dow cautions against using the findings to predict long-term performance of polystyrene foam insulation board in this application.

Interestingly, the foam board insulation testing found that the most common expanded EPS - 2-inch thick, low density (1 lb./ft3), material - held up about as well as extruded stock in both vertical and horizontal insulation board applications. Both showed 2- to 13- percent increases in temperature conductivity after 6- and 18- month exposures.

Dow speculates that the poor performance of the high-density DPS was due to high void content and poor bead fusion. EPS manufacturers agree that good bead fusion is harder to achieve in high-density foam insulating board stock.

Here is a simple test of foam insulating board quality:

EPS should break through the beads, not around them. Because over 175 small companies make EPS foam insulating board products, quality varies considerably. Our photograph of white polystyrene foam board insulation (below) shows broken foam boards at an indoor foam board insulation retrofit project.

Polystyrene insulating foam board indoors (C) Daniel FriedmanWith well-drained soil, a low water table, [protection also from roof drainage spillage against the foundation wall], and a waterproof outer membrane (e.g. polyethylene), a good-quality EPS foam insulation board at least 2 inches thick should perform adequately. To play it safe, some underground builders use EPS toward the inside and extruded insulating board facing the backfill soil around the building foundation.

See BASEMENT HEAT LOSS for a discussion of foundation and basement insulation methods.
See BUCKLED FOUNDATIONS due to INSULATION? for a discussion of insulation's role in foundation damage from freezing soils.
See TERMITE SHIELDS vs TERMITICIDE for a discussion of avoiding insect damage when foam insulating board is used below or at ground level. See WET BASEMENT PREVENTION for other exterior treatments of building foundation walls to combine foundation insulation with basement waterproofing membranes and drainage systems.

Readers should also see POLYISOCYANURATE FOAM INSULATION, INSULATION LOCATION for PASSIVE SOLAR FLOOR SLAB and also RIGID FOAM USE INDOORS. Readers should also see FLOOR, CONCRETE SLAB CHOICES for a discussion of choice of finish floor materials to preserve use of thermal mass of a concrete floor slab. Readers interested in basement insulation improvements should also see INSULATION LOCATION for BASEMENT WALLS and BASEMENT HEAT LOSS.

For more general energy savings advice see ENERGY SAVINGS PRIORITIES, and our insulation home page at INSULATION INSPECTION & IMPROVEMENT. If you are going to insulate under a basement or grade-level concrete slab floor, be sure to read SLAB INSULATION, PASSIVE SOLAR. Finally, readers considering adding insulation inside or outside a basement foundation wall should see POLYSTYRENE FOAM INSULATION as well as BUCKLED FOUNDATIONS due to INSULATION? Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

Foundation Foam Insulation Protection Methods & Advice

  • Q&A: Foundation Foam Protection using Styrofoam - how to protect - original PDF form; use your browser's back button to return to this page.

Question: What finishes are available to protect Styrofoam insulating board used for foundation insulation?

I will be insulating a foundation with Styrofoam. I understand there are masonry finishes available that can be applied directly to the foam or to an intermediate mesh, and that such a surface will hold up to weather exposure. What finishes are available to protect my foundation insulation? - Thomas F. Harter, Oakland CA

Reply: Several Ways to Protect Rigid Foam Foundation Boards

There are several ways to protect rigid foam foundation insulation boards, ranging from pressure-treated plywood to factory-applied stucco finishes.

One pre-finished foundation insulation panel is Thermboard, a 3/4-inch Styrofoam panel coated with a fiber-resin compound that has a stucco-like appearance. It costs [1980's prices] around $`.47 per square foot in the Wisconsin area where it is made. Thermboard is distributed by Georgia Pacific Corp.

Another pre-finished foundation insulation product is Styrofoam FP Panels, distributed by Dow Chemical and available at many lumber yards. The finish is a cementious coating that looks something like concrete.

For a field-applied finish to protect foundation insulation boards, you can trowel on your own stucco to the foam over expanded metal lath, or brush on a finish designed for this purpose, such as Styrofoam Foundation Brush-on Coating (also available from Dow Chemical). It comes in a kit consisting of a dry polymer cement mixture, liquid additive, and fiberglass reinforcing tape [use at seams between foundation insulation boards].

You mix the components with water and apply directly to the foam foundation insulating board. The insulating board is scratched-up to promote good adhesion. It dries to resemble concrete. The cost of this foundation insulation board coating is around 40 cents per square foot. [1986 prices].

[Solar Age 8/86]

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.


Frequently Asked Questions (FAQs)

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Questions & answers or comments about how to insulate building foundations & about using polystytrene insulating board products.

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Technical Reviewers & References

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POLYSTYRENE FOAM INSULATION

  • Solar Age Magazine was the official publication of the American Solar Energy Society. The contemporary solar energy magazine associated with the Society is Solar Today. "Established in 1954, the nonprofit American Solar Energy Society (ASES) is the nation's leading association of solar professionals & advocates. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We advance education, research and policy. Leading for more than 50 years. ASES leads national efforts to increase the use of solar energy, energy efficiency and other sustainable technologies in the U.S. We publish the award-winning SOLAR TODAY magazine, organize and present the ASES National Solar Conference and lead the ASES National Solar Tour – the largest grassroots solar event in the world."
  • Steve Bliss's Building Advisor at buildingadvisor.com helps homeowners & contractors plan & complete successful building & remodeling projects: buying land, site work, building design, cost estimating, materials & components, & project management through complete construction. Email: info@buildingadvisor.com
    Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

  • Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
  • Home Reference Book - Carson DunlopThe Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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  • GO TO Carson Dunlop's Home Study Course Information - How to Become a Home Inspector: Carson Dunlop's nationally recognized Home Study Course, selected by ASHI the American Society of Home Inspectors and other professionals and associations. This website author is a contributor to this course.
  • GO TO Carson Dunlop's Home Study Course Information - How to Become a Home Inspector: Carson Dunlop's nationally recognized Home Study Course, selected by ASHI the American Society of Home Inspectors and other professionals and associations. This website author is a contributor to this course.
  • GO TO Carson Dunlop's Home Study Course Information - How to Become a Home Inspector: Carson Dunlop's nationally recognized Home Study Course, selected by ASHI the American Society of Home Inspectors and other professionals and associations. This website author is a contributor to this course.
    Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd
  • Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
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