As a residential remodeler you will use the International Residential Code (IRC) to govern all aspects of the remodel. For instance, there is a permit requirement for removing a load bearing wall to opn up a room or give a kitchen an open concept. To do this you must read the IRC and understand how you can properly brace the wall while installing a beam. The size of the beam needing to be installed will be governed by the IRC using the span charts. An engineer will have to be involved to provide a letter or drawing and sign off on the plan as in any part of construction but the remodeler should know the detailed requirements as per the IRC to give a proper scope of work to the client and the estimating. Plumbing, Electrical, and any other mechanicals that will be moved during a remodel have to be up to code as dictated by the IRC.