The present invention is a method and system for constructing pre-fabricated buildings. Wall panels are provided wherein each wall panel has a plurality of vertically disposed channel-shaped metal studs equidistantly disposed between a bottom plate and top plate. A substantially rigid foam insert is between each of the channel-shaped metal studs of a wall panel to provide insulation and structural support to the wall panel. The foam inserts each have an aperture forming a conduit vertically disposed within the foam insert. An interior spline is inserted between adjacent wall panels and provides the mechanical connection to secure the wall panels together. The interior spline comprises rigid foam with a pair of steel facing adhered on opposing faces of the spline.