Your access to premium content.
USER NAME: 
PASSWORD: 
   • Register   • Info   • Help

E-mail a friend Printer-friendly version

Insulation Economics
Product Economics

David Johnston, Contributing Editor
April 1, 2001
HousingZone

Inspect
A small void in the insulation dramatically reduces its performance.
It used to be so simple, put the pink stuff between the studs and "rock it!" Today there are more options than ever before—fiberglass, cellulose, spray cellulose, blown-in-blanket, polyurethane, Icynene and structural insulated panels are all insulation options for new construction.

The cost of insulation is a two-sided issue. First cost is always critical to the budget; operating cost of the house interests homeowners. Striking a balance is the key.

On a first cost basis R.S. Means data spells out the economic effects of the various product choices.

Understanding Values
The nominal or clear-wall R-value of insulation is printed on the side of a batt or a bag. It is the thermal resistance of insulation installed perfectly without taking into account the conductance of the studs or other members in contact with the outside wall. On the operating cost side, actual or effective R-value of the wall and roof assembly is the key consideration.

In a study conducted by the Oak Ridge National Laboratory, Jeffrey Christian and Jan Kosny identified the effective R-values for different wall assemblies.

Effective R-values are impacted by several factors:

  • Installation integrity: A small void in the insulation dramatically reduces its performance. A California Energy Commission study showed that a 4% void in attic insulation reduced the effective R-value by 50% in the hottest weather. Studies by Oak Ridge National Labs show similar results. This is reflected in the "rounded shoulder" worst-case line in the chart on page 6.
  • Conductivity of framing materials: Wood studs are less conductive than steel, therefore steel-framed walls have a lower effective R-value than wood with the same insulation levels.

    If the effective R-value is significantly lower than the nominal R-value, the first cost argument needs to be reconsidered. Are you getting what you paid for and most importantly, are buyers getting what they expect?

    McStain Enterprises, a production builder in Boulder, Colo., builds 300 houses per year. Historically, McStain used fiberglass batts exclusively. Over the last few years it switched to spray cellulose insulation in all its homes because customers see the difference in their utility bills says Kristen Shewfelt, McStain’s director of environmental programs. "Though the cellulose is about 25% more expensive, we believe it packs better and seals voids in hard to reach spots like band joists and penetrations. It also provides more comfort for our homebuyers."

    Part of the decision was based on blower door tests conducted at McStain’s Greenlee Park subdivision in Lafayette, Colo. Three models were tested with three different insulting materials—all fiberglass, spray cellulose walls with blown fiberglass in the ceiling, and all cellulose. The blower door tests revealed striking differences. The fiberglass house resulted in just below .6 Natural Air Changes per Hour (NACH). The combination house was .4 NACH and the cellulose house was just over .1 NACH.

    How do you take the next step in improving insulation performance? Learn from those that are doing the research. One is IBACOS, the primary consortium in the U.S. Department of Energy’s Building America Program. IBACOS is a leading public-private initiative focused on bringing systems approaches to the home-building industry Its Home Innovation Network is a collaboration of manufacturers and builders dedicated to the research, development and delivery of better homes and communities. It was established to be the vehicle to realize the IBACOS vision of homes offering unparalleled value and livability.

    Knowing insultation costs—first and operating—and managing its installation are investments that make dollars and sense for you and your buyers.

    Clear Wall Versus Whole-Wall R-Values

    Wall Assembly Type
    Clear-Wall R-Value (Nominal)
    Whole-Wall R-Value (Effective)
    Standard 2x4"
    10.5
    9.7
    Standard 2x6"
    16.5
    13.6
    2x6, batts installed perfectly
    15.4
    12.8
    2x6, batts installed typically
    14.1
    11.7
    2x6, batts installed with rounded shoulders
    14.7
    12.2
    2x6, batts installed with rounded shoulders and
    1-in. gaps at top and bottom
    14.0
    11.4
    Worst-case: rounded shoulders,
    1-in. gaps, and paper fastened to inside of 2x6
    13.2
    11.0
    Steel frame C-stud
    7.3
    5.6
    Steel frame wall with steel horizontal hat channeling
    9.9
    7.6
    Steel frame wall with wood furring strips
    11.3
    8.2
    Steel frame walls with wood frame 2x4s used at interface details
    7.2
    6.8
    Steel frame with polyurethane insulation sprayed into cavity and fiberglass batts
    11.1
    8.2
    Insulation concrete form**
    11.6-12.0
    11.1
    * Second 2 x 6 wall had slightly lower R-value due to presence of electric wiring and use of fiberglass insulation with lower resistivity (3.16 compared to 3.45 h · 12ft2 · °F/Btu · in).
    **Effective R-value of ICF when thermal mass and air tightness is considered: 26-44, depending on climate.

    Also See:

    RS Means Data Comparison - CostWorks Insulation Projects

    Insulation Building Science

    Install: Waterproofing Windows

    Install: Metlund

    Tool Test: Sliding Compound Miter Saws


    © 2008, Reed Business Information, a division of Reed Elsevier Inc. All Rights Reserved.
    •  

    Advertisement




    Sponsored Links
    Radiant Floor Heating
    Cold Floor? Get ThermoSoft Awarded Floor Heating and enjoy!
    Drum Handling Equipment
    Find high quality drum handling equipment at Zorin Material.
    Security System
    Affordable wireless security systems from SafeMart.
    Cabinets
    Looking for a variety of Cabinets for your home? Visit Armstrong.com
    Hardwood Floors
    Stylish and durable hardwood floors from Armstrong
    Cement Mixers
    Find Towable and Portable High Quality Mixers. Fast free Shipping!
    Room Dividers
    Room Dividers at Home Decorators Collection.
    Bamboo Flooring
    Find high quality bamboo floors and other building materials for less.