Installing a sill plate on a crawlspace for a manufactured home. Does it matter if I use spf white wood or treated?
For wood in contact with masonry or concrete, the Code requires the use of an approved species and grade of wood such as decay resistant heartwood of Redwood, Black Locust, or Cedar or pressure treated in accordance with AWPA (See ICC R319.1) in areas subject to decay damage according to Table R301.2(1).
In the U.S., all but the very very most southern portion of the continental U.S. and Hawaii show as “severe” or “moderate”. The remainder shows as “negligible”. I’d consult with your local Building Department if your within that area.
The Code also allows the use of untreated lumber if separated by an approved moisture barrier. (Technically I guess the wood is not “in contact” with masonry or concrete with a moisture barrier.)