A shear panel for constructing underlayments for floors and roofs of buildings includes a first rectangular layer of fire-resistant material, such as cementitious board, bonded to a second rectangular layer of thin high-strength material, such as galvanized steel. The length of the second layer is longer than the length of the first layer. The additional length of the second layer forms a tab extending from one end of the panel. During construction, a first panel is attached to a set of beams (floor joists or roof rafters) with the tab spanning between adjacent beams. A second panel is positioned on the beams with at least a portion of the second panel overlapping the tab of the first panel. The overlapping portion of the second panel is fastened to the tab of the first panel to form a continuous shear diaphragm for the floor or roof.