This is an unusual situation I see from time to time. Water droplet stains on surfaces in the attic. Usually it will appear as dark stains in a random pattern on the insulation or flooring in the attic. You would think it is from a leaking roof, but this is usually not the case.

What is the cause? This was the question that the seller asked me today in a home in Lake Grove, NY.

When attics get hot in the summer, and when the humidity is high, water from the moist air can condense on the nails protruding through the roof sheathing (plywood or tongue and groove sheathing). This causes water droplets to form and drip off the nails onto the surfaces below.

If you look at the stains individually, you will see the stains are directly under the roofing nails. Attics like these need more ventilation. Call a ventilation contractor so a determination can be made, and the problem can be addressed. - Ray