Yard, roof, and field drains refer to underdrains that will drain rain water away from a structure, site, or other area. The pipe material used is typically pvc, hdpe, or clay tile. It is common for an engineer to include a ‘contingency’ of yard, roof, and drain tile replacement in a scope of work for a project. This is essentially a prediction that during the course of excavation on a project, the contractor will come across unexpectedly and damage yard, roof, and field drains which will need to be replaced.