The Amish Lime Wash: A Traditional “Cool Roof”
Element: What It Is, Why It Works
Lime wash: A slurry of slaked lime (calcium hydroxide) powder and water, painted onto roofs. It dries to a bright white, reflective surface — and it is breathable, which helps regulate moisture. Modern people may not be familiar with lime powder, but it was used to make the white outlines on baseball fields using a roller filled with finely ground lime powder.
Pulverised “Garden Lime” (it is alkaline and used to rebalance acidic soil) is on sale for under $6.59 for 40 pounds. (Hills Ace Hardware) May be up to $45 elsewhere.
The cooling effect: White reflects visible light (heat) and some infrared. In hot climates, it reduces heat absorption and keeps buildings cooler — exactly what modern “cool roofs” aim to do.
More reflective titanium oxide is used in modern “cooling” roof paint. It is also white but includes the heavy metal titanium which could have negative impact on the environment if leaching into gutter water, and the ground water supply.
Is It Reflective of Infrared?
White reflects visible light: It looks white because it reflects all visible light which is longer wave length than infrared.
Infrared reflection: Infrared reflection depends on the material. Lime wash is not optimized for NIR/SWIR reflection, but it does reflect some infrared because it is a mineral-based coating.
Modern cool roofs: Use specialized pigments (like YInMn Blue or titanium dioxide) that reflect both visible and near-infrared light.
White Lime wash: It is not as efficient as modern cool roof coatings, but it is better than a dark roof — and it is non-toxic, breathable, and historically proven.
Why This Matters
Traditional knowledge: The Amish (and many other cultures) knew that white roofs stay cooler — without knowing the physics of NIR reflection.
The blue roof pattern": If a directed frequency is in the visible or near-infrared range, a white roof would reflect more of it than a dark or gray roof.
The lime wash is a “cool roof”: It is a low-tech, non-toxic, historically validated solution — and it aligns with biophilic design principles.
The Amish lime wash is ancient, but not a ‘primitive’ solution.
It is a coherent solution — one that works with the physics of light and heat, not against it. Modern cool roofs are its high-tech descendant.
The principle is the same: reflection is protection.
You can see a 10-15% decrease in energy costs by using a white roof according to Secretary Steven Chu, U.S. Dept. of Energy. (Youtube, July 23, 2009) It also reduces air conditioning needs for automobiles or trucks. Light colored pavement or sidewalks also remain cooler. Houses remain cooler in the summer but may be slightly warmer in the winter rather than cooler.
Lighten up, cool down.
Disclaimer: This information is being provided for educational purposes within the guidelines of Fair Use and is not intended to provide individual health care guidance.