Abstract: A building block has opposing like outer members spaced apart by at least two risers as cross members inward from outer member ends leaving a center open with a void between the outer members and the risers. The risers extend from the bottom of the block to above the outer member tops. A continuous tongue projects upward from the top of the outer members parallel thereto along the length of the outer member and mates with grooves along the bottom of a similar outer member stackable thereon for ease of block alignment. A next stacked block is nailed to the risers projecting into its center.