I do not know if lumber/plywood/osb has ever been included in CPI/inflation numbers.
This run up is really unprecedented. I have never seen a run up like this in my 35 year career as a lumber broker. Typically supply increases to meet demand. This time around mills have not been able to increase production.
A 2 x 4 costing over $6 is unreal. I would hate to be building a house. Fortunately the hardwood (oak, walnut, cherry) has not gone up so much.
It has to impact new housing and thus housing costs. However I believe they keep shifting the weights to have minimal official inflation.
Do you know why the mills haven’t increased production? Is it the supply of trees? Covid impacting manufacturing? Ammo is another thing that is sky high. I suspect ammo is not in the CPI though. :)