Parallel chord floor trusses are becoming more common in residential construction (see "Framing With Floor Trusses," 4/93). One reason is that the open webs speed the installation of plumbing, heating, and wiring. Although building codes don't require that pipes passing through a truss space be insulated, there are cases where they probably should be. Though desirable from an energy conservation standpoint, pipe insulation may be unnecessary when the trusses are fully exposed, such as over a basement or a garage. But as this case study shows, problems can arise when uninsulated cold water supply and forced hot water heating lines run through a closed floor truss space. A Sagging First Floor Eight years after its construction in 1984, the owners of the house noticed that the first floor was sagging in