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Assembly-Line Attics

Posted by Green Builder Staff

Sep 9, 2015 3:52:42 PM

The Advanced Residential Integrated Energy Solutions (ARIES) research team has developed a low-cost and easily replicable approach for increasing attic insulation in factory-built homes.

INCREASING ATTIC INSULATION in manufactured housing has been a significant challenge due to cost, production and transportation constraints. The U.S. Department of Energy’s ARIES research team, led by The Levy Partnership Inc., partnered with Clayton Homes’s Southern Energy Homes division and Johns Manville Corporation to develop and test a new attic insulation method that involves dense-packing the shallow attic space in manufactured homes with blown fiberglass insulation before filling the rest of the space with loose fill. With this new method, installers are able to achieve a much higher attic insulation R-value than is typically installed in manufactured homes. The simplicity of this solution bodes well for wide-spread industry adoption.

The Method

To dense-pack the attics, workers at the manufactured home plant use a “mold” consisting of a 24” x 48” sheet of pegboard, with a flange at one end and a hole in the center to receive the insulation tube. The mold is sized to span one rafter bay. The installers start at one end of the house and work their way down, filling each rafter bay from the eave out to the flange.

Once compacted, the fiberglass fibers tend to stay together, so filled bays can be left exposed as the installer moves down the bays. After dense-packing all the eaves, the remainder of the attic is filled with loose blown fiberglass to the desired depth. Baffles are then installed above the insulation to provide a clear path for air to flow from the soffit vents to the roof vents. The house then moves to the next station in the assembly line, where sheathing and roofing are installed.

This hybrid method achieves an average R-value of 44.6, compared to R-33 if it were only to contain loose fill. The method was tested in a home built by Southern Energy Homes to the performance criteria of the DOE’s Zero Energy Ready Home program, which seeks to achieve whole-house energy performance that exceeds the requirements of the 2012 International Energy Conservation Code.

A Scalable Strategy


For the manufacturers, the beauty of this low-tech, low-cost technique is its simplicity and adaptability to current plant production processes. Immediately applicable to the nearly 125,000 new manufactured homes built each year, the technique addresses many industry barriers:

Side by side

Side by Side. The dense-pack roof insulation technique is being tested in a side-by-side comparison with two other manufactured homes—one built to ENERGY STAR standards; the other built to the HUD code.

First cost. Affordability is an industry-defining characteristic. Even significant energy efficiency improvements that could increase the home’s long-term affordability are shunned if they will increase initial home price. The dense-pack technique uses an insulation product that the builders felt provides the highest thermal benefit at the lowest cost. The insulation blower is already in use at most factories, and the cost of the hardboard is negligible. The small cost associated with the dense-packing measure is recovered immediately in reduced overall home operating costs, and the materials have a simple payback of less than three years.

Dimensional limitations. Because manufactured homes are transported over roads, they are subject to strict height restrictions. For example, in California the maximum height allowed is 14 feet, including the wheels, undercarriage, walls and roof. Consequently, attics are low, ranging from 2 to 3.5 feet at the peak and tapering to a heel height of 2.5 to 7.5 inches above the top plates. This leaves very little room for insulation. The dense-pack technique conforms to the constrained space and encourages consistent coverage in every rafter bay.

Production speed. Manufacturers avoid using new products or building methods if they are likely to slow the pace of production, require staff training to build it right and/or are susceptible to defects and recalls. The dense-pack technique uses insulation materials manufacturers are already familiar with in a way that minimizes impact on product flow. The method is simple and easy to learn, and it is easy to verify quality—major advantages in a high-paced production setting. Adoption could be implemented immediately on a large scale across companies without the need for retooling or other process changes.

Clayton Homes Southern Energy

Easy as 1-2-3

Step 1: An employee at Clayton Homes’s Southern Energy Homes plant uses a perforated hardboard “mold” to dense pack blown fiberglass insulation into the eaves of a manufactured home. The light-weight mold is 4 feet long and just wide enough to span the rafter bay. A flange at the far end holds the insulation in place as it is blown in.

Step 2: Installers start at one end of the house and work their way down, filling one bay at a time in about 23 seconds per bay.

Step 3: After all of the eaves are dense-packed, the remainder of the attic is filled with loose fill to the desired height.

A first in Zero-energy-ready homebuilding

A First in Zero-Energy-Ready Homebuilding

Clayton Homes’s Southern Energy Homes subsidiary completed the first DOE-certified Zero Energy Ready manufactured home in Russellsville, Alabama, last year. In addition to meeting all of the requirements that site-built homes must meet to qualify for the high-performance home labeling program, it meets the standards of ENERGY STAR 3.0 and incorporates the indoor air quality and water-saving measures of the U.S. EPA’s Indoor airPLUS and WaterSense programs.

The home was built with wood-framed walls (2 x 4 studs spaced 16 inches on center) and some advanced framing techniques; for example, there are no extra studs at the doors and windows. To cut heat loss, caulk was applied around every plumbing, wiring, ducting and vent stack hole in the floors and ceilings. In addition to installing R-13 of unfaced fiberglass batt insulation in the wall cavities, the exterior of the walls was covered with a 1-inch layer of XPS rigid foam insulation sheathing, which was fastened to the studs with adhesive. The insulation values are R-54.6 in the ceilings, R-13 + R-5 in the walls and R-28 in the floors, well above 2012 IECC requirements for its climate zone.

The home also uses a new HVAC design that keeps the HVAC equipment completely within the home’s conditioned space. It is equipped with a super high-efficiency, mini-split heat pump with a SEER of 22 and a heating season performance factor (HSPF) of 12.

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