How to insulate around basement I-beams

A homeowner in Nebraska is renovating the basement of a 1926 house with block foundation walls and ran into a common snag. The original plan was rigid foam insulation (1 inch of XPS) against the foundation wall, then a 2x4 stud wall filled with rock wool insulation. But the basement has steel I-beams installed every 4 feet or less, each 4 inches deep, and those beams create a path for heat to escape straight through the wall assembly, bypassing the insulation. This kind of heat loss around framing members is called thermal bridging.

The beams also throw off the stud spacing. Since the plan is to build the wall between the beams, most stud bays will not land on the usual 16- or 24-inch centers, making it harder to fit standard insulation batts neatly.

This is a question posted to a building-science forum rather than a finished how-to, so no specific fix or product recommendation has been settled on yet. For a homeowner facing something similar, the takeaway is that basements with exposed structural beams need extra planning before insulation goes in. Beams that cut through the wall plane can undercut the R-value of an otherwise good insulation job, and irregular framing bays complicate how insulation gets installed. If your own basement has steel beams or other framing that interrupts the wall, it's worth having someone look at how the insulation layers wrap around them before the walls get built.