Abstract: A bottom construction for a shaft furnace, has a plurality of horizontal layers of refractory material, and a gastight metal membrane located above at least the lowest layer of refractory material. So that the membrane is easily constructed, can accommodate thermal movements and has a level upper surface, the layer of refractory material immediately underneath the metal membrane is formed of blocks and has a level top surface and the metal membrane is formed of loosely laid, mutually abutting metal plates which are stacked in at least three layers. The pattern of the joints of the plates of each of these three layers is offset, as seen in plan view, with respect to the pattern of the joints of both the other two layers. The plates may be copper sheets. The membrane may have a peripheral flange cemented in a slot at the furnace wall.