A spar assembly for a rotor blade of a wind turbine is disclosed. The spar assembly may generally include a first spar cap and a second spar cap spaced apart from the first spar cap such that a cross-sectional area is defined directly between the first and second spar caps. Additionally, the spar assembly may include a web having a first end disposed adjacent to the first spar cap and a second end disposed adjacent to the second spar cap. The web may be configured such that at least a portion of an inner surface of the web is disposed outside of the cross-sectional area.