We are thinking about gutting our house. My husband thinks it would be a great idea to rip out all of the walls and ceilings. We have foundation problems, a possible ventilation problems, definite plumbing issues. Would it be better to take down all the drywall, check the plumbing and ventilation throughout the entire house OR troubleshoot those problems leaving the drywall up.

If you are thinking of buying a house that is in bad condition, then you should be hiring an inspector to tell you what has to be and how much. You could be throwing good money after bad.

No I don't think it's a good idea to rip out all the drywall and replace if it isn't entirely necessary.

We have lived in our house for 6 years now. The foundation has gotten progressively worse - so we know we will have to fix that. We were just told my an HVAC guy that he thinks some of our ducts are blocked with sheetrock. (He is a really good guy - I trust what he says). We have leaks in an upstair bathroom that is causing mold in our downstairs master bath.

You'd typically only take down what you need to do the repairs. That's the nice thing about drywall.

The problem with taking down all the drywall it not the expense of doing that... it'll be all the other things you might decide to do since the walls are open such as re-plumb the house, re-wire, re-insulate, move walls, new flooring, new kitchen and bathrooms, etc. It'll be hard to stop from doing a complete reno. Doing all of it also means you'll need to move all your furniture out and find a rental. It could cost significantly more than just repairing the problems you mentioned.

So what is the foundation problem? I'm concerned that it is getting worse.