Abstract: A system for assembling structural insulated panels (SIPs) includes a set of splines that snugly insert into channels along the top, bottom and side edges of each SIP. Vertical alignment splines are used to align and connect adjacent SIPs and horizontal plate splines are used to cap edge channels of a SIP such that the edges of the SIP can securely rest on, support or be affixed to a foundation or other structural member. The system components facilitate fast and precise alignment, interconnection and installation of SIPs in order to form walls, floors, roofs or foundation systems.