The dropping of water from the under side of a corrugated iron roof is caused by the moisture of the warm atmosphere of the room condensing on the colder surface of the iron roof, and this condensation, of course, goes on more rapidly during frosty weather. The remedy is to fix at the bottom of each sheet of iron a small half-round gutter to catch the water. Lead it to one end of the roof, and bring it to the ground by a down pipe. A lining of slag wool or silicate cotton supported by matchboard will prevent the condensation sometimes.