> but can we find ways to use alternative building materials that don’t require a tree to grow in the ground for 20+ years?

Trees are an incredible renewable resource. Most homes today are built with trees from managed, sustainable forest and LVL's (laminated veneer lumber) from the same sources. The LVL's replace "big beams" for old growth. The "frame" of an average house now looks like this: http://www.joneswholesale.com/products/images/ROS-RFPI-Solid...

Anysort of concrete/hempcrete/whatever is actually going to be a terrible thing for the environment compared to... wood.

Between LVLs, Glulam beams, and CLT what you should be asking is why arn't more midsize buildings built of wood instead of environmentally disastrous concrete. See this for example: https://www.popsci.com/article/technology/worlds-most-advanc...