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This article was originally published in the March/April 1994 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.

 

 

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Home Energy Magazine Online March/April 1994


FIELD NOTES

News of local, state, federal and utility programs

 

 


Hide `n' Seek Savings

This old house (pre-1940s) got the works. Two separate weatherization programs (utility- and state-funded), plus a low-interest rehabilitation loan, had already paid for extensive retrofit work. The place looked great, but the utility bills didn't go down. What happened to the savings?

The first crew insulated the attic, tuned up the boiler and repaired the venting system. The utility program did not require a blower-door test, so no pre- or post-weatherization measurements were taken. After the initial weatherization work, the weather-adjusted natural gas consumption actually increased from 134 MBtu to 166 MBtu per year.

The second program installed sidewall insulation and performed a pre- and post- blower door test on the house. This work resulted in only a 3% reduction in air leakage (from 5,423 CFM50 to 5,232 CFM50).

The low-interest loan installed new windows, doors, and siding. After this work was completed, air infiltration in the house was still at 4,900 CFM50, though natural gas consumption dropped down to 127 Mbtu per year, for net savings of only 7 Mbtu per year.

At first glance, the relatively small (1,030 ft2) two-story home seemed simple enough, but closer inspection with a blower door and infrared camera revealed a major oversight. The sidewall cavities opened into the living room ceiling cavities, which in turn opened into the stairwell framing that opened into rafter cavities that led to a well-ventilated attic. Thus the framing in the house served as a complicated heat-loss duct system, which took heated air straight into the attic and the great outdoors.

Despite the considerable work and expense that had gone into it, the house was still using essentially the same amount of natural gas, and it leaked like a barn. How did so many people miss so many things and produce so small a result?

The critical connections between the attic and the rest of the house were not sealed. Rafter cavities, partition wall cavity openings, and the attic hatch were either not treated at all or were only partially sealed. If a blower door test had been conducted before the attic insulation was installed, the work probably would have continued and the attic would have been properly sealed. A simple attic zone pressure measurement, while opening and closing closet doors, clearly showed the direct connection between the attic and the house via the rafter slopes.

Connections to the walls were not treated as a primary thermal bypass. The second crew conducted a pre-weatherization blower door test, installed wall insulation, did the required post-weatherization blower door test--and then packed up and left. The blower door was available for them to use as a tool to further investigate why the air infiltration rate remained so high, but the crew did not use it to look for the cause.

Exterior wall cavities opened into a dropped living room ceiling, and that cavity opened into a linen closet on a stairway landing, which in turn opened into the partition walls and stairwell, and ultimately to the attic. The attic-zone pressure jumped up and down when the linen closet door was opened and closed. Special attention to the wall/ceiling juncture and high-density insulation techniques were needed to control the thermal boundary.

This small, seemingly simple house defied everyone who came in contact with it. Complicated houses, large or small, don't always respond to work the way we think they should. Installation techniques and work quality that would have achieved some level of savings on a simpler house had little or no effect on this one.

When work on the house began, the roof deck and the siding formed the thermal boundary, and that boundary had not changed when the work was finished. The interior framing system should have been isolated from the attic and the sidewalls. It was not.

What is the moral of the story? Programs need to move past the practice of taking tests, dutifully writing the numbers down on forms and then doing things the way they have always been done. The numbers are only useful when they help us improve our performance and learn another lesson about another house.

-- Don Jones

Don Jones is with Homewise in Hebron, Ohio.

 

 


Figure 1. Air leakage pathways in the problem house.

 



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