A lap siding product, comprising: an elongated rectilinear panel with a length, a front side and a back side with a thickness therebetween, and a first edge and a second edge with a width therebetween; a central front side cut extending the length of the panel midway between the first edge and the second edge, said central front side cut having a depth extending half or more of the thickness of the panel; wherein the panel is configured to be divided manually along the central front side cut into a first lap siding piece and a second lap siding piece; characterised in that: the lap siding product comprises: a first back spacing cut positioned along the first edge of the back side and extending the length of the panel; a second back spacing cut positioned along the second edge of the back side and extending the length of the panel; wherein the first back spacing cut and the second back spacing cut are to assist in the horizontal location of the pieces of lap siding with respect to each other during installation by allowing the back spacing cut on the bottom of a piece of lap siding to sit on the top of an already installed piece of lap siding. an elongated rectilinear panel with a length, a front side and a back side with a thickness therebetween, and a first edge and a second edge with a width therebetween; a central front side cut extending the length of the panel midway between the first edge and the second edge, said central front side cut having a depth extending half or more of the thickness of the panel; wherein the panel is configured to be divided manually along the central front side cut into a first lap siding piece and a second lap siding piece; characterised in that: the lap siding product comprises: a first back spacing cut positioned along the first edge of the back side and extending the length of the panel; a second back spacing cut positioned along the second edge of the back side and extending the length of the panel; wherein the first back spacing cut and the second back spacing cut are to assist in the horizontal location of the pieces of lap siding with respect to each other during installation by allowing the back spacing cut on the bottom of a piece of lap siding to sit on the top of an already installed piece of lap siding. the lap siding product comprises: a first back spacing cut positioned along the first edge of the back side and extending the length of the panel; a second back spacing cut positioned along the second edge of the back side and extending the length of the panel; wherein the first back spacing cut and the second back spacing cut are to assist in the horizontal location of the pieces of lap siding with respect to each other during installation by allowing the back spacing cut on the bottom of a piece of lap siding to sit on the top of an already installed piece of lap siding. a first back spacing cut positioned along the first edge of the back side and extending the length of the panel; a second back spacing cut positioned along the second edge of the back side and extending the length of the panel; wherein the first back spacing cut and the second back spacing cut are to assist in the horizontal location of the pieces of lap siding with respect to each other during installation by allowing the back spacing cut on the bottom of a piece of lap siding to sit on the top of an already installed piece of lap siding.