My tiny central New Jersey home is about 100 years old. I'm not sure what type of contruction it is called, but there is no sill plate, meaning that behind the plater & lath wall there is an opening from the basement to the atic. Every so often, especially in the winter months, we have what appears to be sticy yellow sap running down some walls from the ceiling to the baseboard. This week, I've noticed alot of it in my bedroom which was painted about a year ago on the outside wall. The wall feels damp when the others don't. That side of the house faces about south east and receives a lot of sun all day. What is this sticky substance, why is it happening and how do I stop it?