Building panel

A wall structure comprising a plurality of rectangular substantially flat blocks positioned in a plurality of horizontal rows in edge-to-edge relationship to form an outer wall, a second plurality of rectangular substantially flat blocks positioned in a plurality of horizontal rows in edge-to-edge relationship to form an inner wall spaced from said outer wall, the inner faces of said blocks each having a plurality of vertically extending grooves therein such that the grooves of the several rows of blocks are aligned, an elongated spacer member vertically positioned in one pair of opposed rows in each block of said inner and outer walls and extending from top to bottom thereof, and elongated spacer members of varying lengths are positioned in abutting relationship in another pair of opposed rows in each block whereby the uppermost of said last mentioned spacer members extend upwardly into alternate grooves in a block of a row thereabove, and means interposed between said spacer members and straddling and embedded in vertically abutting blocks of each row for clamping horizontal edges of opposed blocks in said inner and outer walls to align the panels in position.