First the details - This is a second home and we're here around 1-3 weekends a month. The house is a raised ranch style log house in the Southern Berkshires (MA) - a cold, rainy, damp place. The basement / lower level is partly under the ground level and partly above. It gets pretty damp in the spring, summer and fall. Last weekend it was 82% RH in the basement as the dehumidifier had failed. I replaced the dehumidifier and it's all well in the basement floor / lower level now and close to the 50% RH I've set on the dehumidifier which drains continuously into a drainage pipe. The upper level unfortunately still has 70% RH. There is no air-conditioning and no house exhaust fan. In the winter, the heat (electric) keeps the humidity fairly low and there is no issue.
How do I reduce the RH levels in the upper level of the house? When we're at the house, if it gets hot, we open the skylights and turn on the fan - this cools the living space but the RH level is still around 70%. Outside RH is in the 50%-60% range in spring, summer.