About one-fifth of all manufactured homes were built before standardized building codes were put into effect in 1976. There are an estimated 4.3 million manufactured homesites nationwide, according to the Manufactured Housing Institute. Solís authored a report on extreme heat’s effect on mobile home residents and found that in Maricopa County, mobile home residents are six to eight times more likely to die from extreme heat. But these changes aren’t enough to protect mobile home residents from extreme heat. “Manufactured housing… could actually be a great solution.” New manufactured homes cost less than single-family homes to build.