When walls and ceilings in a building are poorly insulated, with low temperatures outside, they are cold to touch. When there is no insulation or it is poor, it is easy for water to condense on surfaces, so damp and mold on walls and ceilings may appear.

When all windows and doors in a building are closed, you should not feel cold drafts anywhere, and if there are, the draft should be light. Air leaks (air intake from outside) usually occur next to windows and doors, shutter boxes, or through sockets. An easy way to check it is to lit an incense stick and see if the smoke drifts. Another way is paying attention to a potential “hiss” caused by air intake.