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A radiant barrier — a reflective sheet installed in the attic that turns back the sun's heat before it reaches the rooms below — is one of the cheaper and simpler energy upgrades an old house can get. A study funded by the National Park Service asked what it actually does for small historic homes in a hot, humid climate. The short answer: it usually helps, by about 6–7 percent of total energy use, and it pays for itself in roughly 14 years — with a wide spread from house to house.
The study
| Who | the Center for Cultural Sustainability, College of Architecture, Construction and Planning, University of Texas at San Antonio |
| Led by | Professor William A. Dupont, with Dr. Hazem Rashed-Ali, Dr. Randall D. Manteufel and Dr. Suat Gunhan |
| Funded by | the National Park Service's National Center for Preservation Technology and Training (grant P14AP00143) |
| What | energy use measured before and after a radiant barrier was installed |
| Homes | six one-storey historic houses, small: 1,381 sq ft on average, 1,404 sq ft median |
| Climate | zone 2A, hot and humid |
The point was practical. Owners of older homes need to know which upgrades are worth it, and there was little measured evidence for this one in a real historic house.
What it found
All results are adjusted for differences in weather between the years compared.
| Measure | Result |
|---|---|
| Change in total energy use, average | −7.2% |
| Change, median | −5.9% |
| Best case | −25.5% |
| Worst case | +4.2% — one home used more |
| Installation cost, average | $1,544 |
| Installation cost, median | $1,228 (one costly outlier raised the average) |
| Simple payback, from the medians | about 14 years |
Fourteen years is a good payback next to other retrofits, though not an exceptional one — and with results ranging from a quarter less energy to slightly more, six homes are too few to lean hard on a median.
Why small houses are harder
The smaller the house, the less energy it uses to begin with, so any retrofit has less to save in percentage terms. The researchers' conclusion: in general, the smaller the home, the longer the payback you should expect from an upgrade like this.
What to study next
- More homes, for more reliable numbers.
- Installation cost, especially labour, which makes or breaks the finances of this retrofit.
- Heating. In a climate where cooling is supposed to be the bigger load, the homes' natural-gas energy use intensity came out 35% higher than their electric — unexpected, and still unexplained.
Sources
Written from "Radiant Barrier Retrofits to Improve Energy Efficiency of Older Homes in Hot-Humid Climate Zones," National Center for Preservation Technology and Training, National Park Service; a work of the United States government in the public domain.
Лицензия: CC0 1.0 (общественное достояние) · По материалам www.nps.gov
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