Abstract: A sidewall plank (14) for constructing trailers and an associated sidewall construction (10). The sidewall plank (14) has an body (15) defining a first edge portion (17) and has a second edge portion (19) for engaging the first edge portion (17) of another plank (14). The first edge portion (17) of the sidewall plank (14) defines a tongue (18) and the second edge portion (19) defines a primary groove (20) for receiving the tongue (18) of another sidewall plank (14). The first edge portion (17) also includes a second groove (24) for receiving an adhesive/sealant material and the second edge portion (19) is provided with a third groove (26) for receiving an adhesive/sealant material and for registering with the second groove (24) of another plank (14). The associated sidewall construction (10) includes a plurality of sidewall planks (14), and a roof support member (30).