One of the oldest and most sustainable building materials of all time is staging a comeback: hemp. Now that several states have legalized the use of marijuana for some recreational and medicinal purposes, a big untapped market is emerging for cannabis to be used as a building tool.

Across America a grassroots effort is underway among builders, architects, material suppliers and farmers to renew this fledgling market. Mixing hemp’s woody core with lime and water produces a natural, light concrete that retains thermal mass and is highly insulating. No pests, no mold, good acoustics, low humidity, no pesticide.It grows from seed to harvest in about four months.

A catalyst that may spark growth in hemp home building is Senate Majority Leader Mitch McConnell’s, R-Ky., Industrial Hemp Farming Act of 2018, introduced last week.

If passed, the bill — co-introduced by Sen. Rand Paul, R-Ky., Sen. Ron Wyden, D-Ore., and Sen. Jeff Merkley, D-Ore. — will remove industrial hemp from Schedule I of the Controlled Substances Act and allow it to be regulated as an agricultural crop. The bill will also authorize and encourage access to federal research funding for hemp and remove restrictions on banking, water rights and other regulatory barriers the hemp industry currently faces. A companion bill has been introduced in the House.