I am wondering how different installers install around the country. Do you leave an expansion gap when installing solid nail down or do you cut tight against the baseboard moldings?

Since the rules are written to leave a gap, that is what is best to do.

Now with that said, some old historic homes, you cannot disturb the baseboards, and you cannot install shoe or quarter round. That is when you better fully understand wood science.

Howard told us in class, about historic homes around the Boston area and the restrictions placed on restoration.