Summary
Highlights
Modern roofs absorb significant heat from the sun, radiating it into homes and increasing air conditioning costs. The average American family spends over $700 each summer on cooling, and new AC systems can cost tens of thousands over their lifetime. 93% of heat entering through a roof is radiant energy, not hot air, and dark asphalt roofs can reach 160°F, leading to attic temperatures of 140°F or higher.
The Amish utilize natural and time-tested methods to keep their homes cool. They use light-colored metals or slate for roofs, apply limewash (a mixture of hydrated lime and water) to exterior surfaces to reflect sunlight, and design their houses with features like north-facing orientation, overhanging eaves, high ceilings, thick thermal mass walls, and cross-ventilation. A separate summer kitchen prevents cooking heat from entering the main house. These methods cost less than or nothing compared to air conditioning.
In 1973, Lawrence Berkeley National Laboratory confirmed that a limewashed roof could drop surface temperatures by 40°F and interior temperatures by 8°F. This concept is not new; ancient civilizations like the Minoans, Egyptians, Persians, and Native Americans used similar reflective coatings or seasonal mud applications to cool their homes. King John ordered whitewashing in London in 1212 for fire retardation, another benefit of lime.
Despite the proven effectiveness, American roofs are predominantly dark. The Asphalt Roofing Manufacturers Association (ARMA) has actively lobbied against ordinances requiring or encouraging reflective roofing, claiming dark roofs are more efficient or that white roofs cause problems like condensation and mold (claims disproven by independent studies and large-scale tests by retailers like Target). This suppression benefits the multi-billion-dollar HVAC and roofing industries as hydrated lime is cheap, unpatentable, and threatens their revenue model. Homeowners associations also often forbid reflective roofs.
To apply limewash, homeowners can purchase a 50-lb bag of type S hydrated lime for $7-$14. Mix one part lime powder with two parts water to a thin milk consistency. Apply two coats with a roller or brush, allowing plenty of drying time between coats. For a 1,200 sq ft roof, costs are $14-$28. A Texas homeowner documented a 46°F attic temperature drop and $1,200 in electricity savings. Limewash also offers antibacterial, antifungal, fire retardant, and insect-repelling properties.
In 1959, NASA developed reflective foil sheets to manage extreme temperatures in spacecraft. By 1963, this technology, known as a radiant barrier, was tested for residential attics. It intercepts infrared radiation, dropping attic temperatures by 30°F and reducing AC runtime by 40-70%. A Phoenix homeowner saw a $187 monthly electricity bill drop for a $54 material cost. Radiant barriers are available for $30-$60 per 500 sq ft roll, stapled to the underside of rafters with an air gap. This technology was quietly removed from residential construction manuals in 1991, leaving a generation of builders unaware, while the dominant fiberglass insulation (effective against conduction and convection but not radiant heat) continued to be promoted.
Air conditioners move heat horizontally into warm outdoor air, making them inefficient. White limewashed surfaces, however, employ radiative sky cooling, moving heat vertically into the sky, which acts as a heat sink at -50°F to -70°F. In 2021, Purdue University created the most reflective white coating, generating 10 kW of passive cooling power for 1,000 sq ft, outperforming a standard central AC unit without electricity. Combining limewash and a radiant barrier provides a dual system addressing nearly 100% of radiant heat for around $70-$90 and a weekend's work, providing cooling without electricity bills.
The video argues that simple, effective, and inexpensive solutions like limewash and radiant barriers were suppressed by industries that profit from expensive HVAC systems and dark roofs. The knowledge was never lost but set aside for profit. The presenter encourages viewers to share their experiences with attic temperatures, lime wash, or radiant barriers in the comments to help others. He also teases an upcoming video about Amish well water systems that eliminate the need for expensive appliances.