What is the most expensive part of building a home?
Structure and mechanicals take the biggest slice.
Quick answer: Foundation, framing, and roofing typically consume the largest share of a new-home budget, followed by HVAC, electrical, and plumbing.
In a new build, the structure consumes the largest slice of budget. Foundation, framing, and roofing often total 35-45% of overall cost because they combine heavy materials, cranes, and skilled labor. Site work—grading, utilities, and driveways—adds upfront expense before any finishes appear.
Mechanical systems come next: HVAC, electrical, and plumbing together can run 15-25% depending on code requirements and house size. Energy codes and seismic or wind zones can push structural and mechanical pricing even higher.
Cost drivers to watch
- Complex rooflines and tall walls that add framing labor.
- Poor soil requiring deep footings, piers, or engineered slabs.
- Long utility runs for rural lots and private wells.
- Custom windows, large spans, or steel beams for open plans.
Interior finishes feel expensive because you choose them last, but they typically represent a smaller percentage than the core shell. Lock your structural scope first, confirm engineering early, and leave a contingency for hidden site conditions.