Holes Weaken Floor Joist
Any holes, cuts or cracks will weaken the floor
joist, no matter how small they are. There are certain areas where you
can drill holes or cut notches in the floor joist and all of these areas
should be understood by all home inspectors.
Look at the illustrated charts in the structural area of this website for more information on drilling and notching floor joist.
Most holes in the floor joist can be eliminated with proper planning of the rough plumbing. However there will be times when the plumber will have to go through a floor joist to make something work.
Most structural beams can not be drilled or notched and if you run across a situation like this, during a home inspection, you should advise your clients and make a note of this in your report.