How to build homes that can survive extreme heat

Recent heat waves in Europe and the U.S. have exposed a weakness in how American homes are built. Since air conditioning became common after World War II, builders largely stopped designing for climate: thick walls, shaded porches, high ceilings, and airflow-friendly layouts gave way to cheap drywall and boxy floor plans, on the assumption that AC would handle the rest. That works fine until the power goes out. Researchers estimate a two-day blackout during a heat wave in Phoenix could kill nearly 13,000 people. Power outages nationwide have doubled over the past two decades, and heat deaths tied to outages, including after Hurricane Beryl in Texas, have already happened.

Some fixes are simple and cheap: facing a house away from direct sun, adding awnings or trees for shade, using gravel instead of asphalt, or painting a roof white to reflect heat. Painted "cool roofs" alone could cut Phoenix's blackout death toll by 66 percent, per one study. Mobile homes, which house a large share of heat deaths, benefit from skirting around the foundation to block hot air and from small additions like trellises.

For new construction, "passive house" building — using airtight, well-insulated walls so a home holds its temperature like a thermos — can cut cooling costs by up to half and needs far less energy overall. In Massachusetts, such homes cost only 2 to 3 percent more to build than standard ones. Federal tax credits that once offset those costs have been cut or allowed to expire, so availability may depend on what your state or city separately offers.