The cost of construction is rising again. Trade disputes, hurricanes and rising demand from overseas are all pushing up the price of materials from gypsum wallboard to lumber and steel. …The price of wood is a big worry for apartment developers. After the Presidential election, the Trump administration threatened to add tariffs on Canadian lumber, on the grounds that the Canadian government illegally supports its timber industry. This disagreement has come up before—and the last time it did, the price of lumber more than doubled and stayed high for years. …Prices for lumber and plywood rose 6.8 percent over the year that ended in September. Most of those price increases came earlier this year.