SIPs Outperform Stick & Batt  (Oak Ridge National Labs R-Value Test) 

When someone says "R-value", what they're really talking about is resistance to heat flow in a given medium, such as fiberglass insulation. The higher the number, the greater the resistance. So when a builder is asked "What's the R-value of this wall?", the natural lination is to think of the material that most commonly specifies its rating. More often than not, it's the insulation, and the response is something along the lines of "Oh, that wall has an R-value of 24" - fairly impressive, but also strikingly inaccurate.

It's not that the builder is intentionally misleading his client or associate, but that he's just following common practice. In reality, this reasoning doesn't take into account all the other components that go into making a wall: wood or steel studs every 16" or 24", bracing, nails or screws, wiring and switch boxes - any number of things that are not insulation, and in all likelihood, have R-values that fall well short of the stated R-24.

A new study by the Oak Ridge National Labs (ORNL) proves that a 4-h SIP wall outperforms 2"x4" stick and batt construction, and even edges out 2"x6" construction in terms of thermal performance. Because SIPs are the structural elements, there are no studs or braces to cause breaks in the insulative action. The end result is a more comfortable, energy efficient structure that performs up to spec in real-world conditions. Unlike stick and batt construction, which can be subject to poorly installed - even missing - insulation, the nature of SIPs is such that the structural and insulative elements are joined as one. There are no hidden gaps, because a solid layer of foam insulation is integral to panel construction.

By contrast, state-of-the-art technical analysis of whole wall performance indicates that the losses in a stud wall are much greater than you might think: on average, the other standard components in stick and batt construction can reduce R-values in as much as 30% of the wall area. Fortunately, that's not the case with structural insulated panels. The ORNL study found that SIPs perform at approximately 97% of their stated R-value overall, losing only 3% to nail holes, seams, splines, and the like. Wiring chases are precut or preformed into the foam core, providing a continuous layer of insulation keeping the elements at bay and the interior free of drafts and cold spots.

A SIP wall also outperforms stick and batt when it comes to maintaining consistent interior temperatures, and that translates to improved occupant comfort. As shown in the graph below, the interior surface temperature of frame construction drops precipitously at every stud, while the SIP wall remains consistent across its entire surface. No temperature dips mean improved occupant comfort, regardless of where you are in the room. That's a big part of what people are talking about when they say they can immediately "feel the difference" in a SIP-built residential or commercial space. With SIPs, thermal efficiency and comfort are built in at the factory, and now the lab results prove it.

Interior surface temperature comparisons indicating constant temperature for SIP wall and reductions in temperature at stud locations for 2"x 4' and 2" x 6" wood frame walls (ORNL).



Energy Savings

"If you are not using SIPs as your core building material you are not serious about energy efficiency."

Michael Morley, Builder & Author - "Building with Structural Insulated Panels"

Energy Payback

There are five reasons foam-panel homes should have lower heating and cooling bills than homes insulated with common wall and ceiling insulation materials:

  • Structural Insulated Panels achieve thermal ratings of between R-4 and R-7 per h; batt and loose-fill materials are about half that.
  • With less wood, panels reduce thermal bridging (the transfer of heat into or out of a structure through a solid piece of lumber). A 16-foot SIP wall section with one 3 x 4-foot window contains 5 percent wood and 95 percent Insulation. The same wall framed with 2 x 4s 16 o.c. has 20 percent wood and a variable amount of insulation.
  • If not installed properly, batt insulation is susceptible to voids. Batts are either jammed into narrow cavities, improperly split around wiring or around electrical boxes, or cut too short or too long. In some remodeling jobs, insulation is removed, but not replaced. When used with a trussed roof system, batts won't cover up the bottom chords, allowing heat to transfer directly from the interior of the house into the attic area in the winter and from the attic into the house in the summer. A solid foam panel eliminates these problems.
  • Any air moving within a conventionally insulated wall or ceiling decreases the energy performance of batt insulation. When properly sealed, foam panels do not allow air movement.
  • Depending on proper installation and effective sealing of joints and openings, Structural Insulated Panel (SIP) construction lends itself to tighter-than-average construction. This is especially true when SIPs are used for both walls and ceiling because the systems are engineered to connect to each other easily and tightly.

Energy Tables

R Value Panel Thickness Weight (PSF)
16.87 4.50" 3.31
25.60 6.50" 3.47
33.20 8.25" 3.61
41.90 10.25" 3.78
50.60 12.25" 3.95

Place: Watertown, S.D.
Heating degree days: 9,000

Size of home: 1,040
square feet with a full basement, identical floor plans

Energy source: Natural gas, forced-air furnace

  Conventional frame Panel frame
Walls 6' fiberglass batts with 1" foil sheathing; R-24 5"EPS-core panels, R-24
Ceiling 12" fiberglass; R-38 71/2" EPS-core panels, R-32
Main floor Main floor and basement
Heating bill
$263 $85
Source: Enercept, ., Watertown, SD



Place: El Jebel, Colo.
Heating degree days: 7,635

Size of home: 1,336 square feet

Heating source: Electric baseboard; HRV

  Conventional 2 x 6 frame Panel frame
Walls 51/2" fiberglass batts plus 1/2"exterior Insulated, R-22 with airtight drywall (5/8") R-22
Ceiling Fiberglass batts, R-38 (R-30 in slope) R-38
Heated area Whole House Whole House
Heating bill
$450 $112
Source: Big Horn Construction Services, Carbondale, Colo.



Place: Ludlow, Mass
Heating degree days: 5,600

Size of home: 2400 square feet

Heating source: Electric

  Conventional 2 x 6 frame Panel frame
Walls 51/2" fiberglass
batts, R-19
Ceiling 9"Fiberglass batts, R-30 R-33
Heated area Whole House Whole House
Heating bill
$131/mo $30/mo
Source: Waverly Heights Development Corporation, Ludlow, Mass.

The walls of this Idaho State Liquor Store in Nampa, Idaho (pictured above the tables) are 6.5" thick (R 25.6) and 9' high. Most panels measured 8' wide x 9' high. The total square footage of this building is 2,990 square feet and the walls were installed in one day. The General Contractor on this project was Sage Construction of Caldwell, Idaho.

According to the Idaho State Liquor Dispensory, the building saves them operating expenses every month. There is a similar building located approximately 10 miles away in Caldwell, Idaho that has a total of 3,010 square feet and was framed using 2 x 6 studs at 16" on center. Below is the comparative energy costs for the (2) buildings during the winter of 1997 / 1998:

  Building 1 Building 2
  2 x 6 Stick Frame 6.5" Precision Panel

December 1997

$158.92 $38.45

January 1998

$176.46 $64.85

February 1998

$112.85 $29.36

March 1998

$72.81 $22.07


$521.04 $154.73
Savings over a 4 month period = $366.31



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