Make sure your refrigerator door seals are air tight. Test them by closing the door over a dollar bill. If you can pull the bill out easilly, the latch may need to be adjusted or the seal may need to be replaced.
Ventilation for crawl space and basement areas is a necessary in preventing mildew, musty odors, and even rot.
One way to help either screws and nails penetrate wood without splits is to use beeswax on the fastener. In fact, some carpenters will drill a hole in the end of a wood hammer handle to fill it with beeswax. An alternative is to buy a wax seal for a toilet. It's made of beeswax processed to stay soft, and costs much less.
If you suspect your toilet is leaking, but aren't sure where, add some food coloring to the water in the tank. If you see colored water inside the toilet bowl, suspect a defective flapper that needs to be adjusted or replaced. If it shows outside the toilet near the back, suspect a faulty tank-bowl gasket. If you see any water on the floor near the base, check for a faulty wax ring.