How much basement moisture is tolerable/ normal and how to tell if a french drain or other precautions are necessary?

[Adam Olsen]

It's necessary that I replace the floor in the basement of my duplex. I'm in the process of breaking out the old concrete and the earth under is wet. I understand that there should be moisture in the dirt but how wet is too wet and how do I figure out if an interior french drain and sump pump is necessary?

A little more information

Located in Salt Lake City.

Evidence of moisture on some of the walls including under a window well.

The old floor was a really bizarre construction. There was about 2 1/2" of concrete poured and 2x4s set directly in the concrete on 16" centers and used as floor joists and a plywood sub floor on top. This was not discovered by me or my home inspector while doing due diligence. When I began tearing out the old floor about half of the wood was moldy and rotted.

With this evidence of moisture I want to make sure I proceed with the rebuild correctly to avoid problems down the road.

Thoughts, advice and recommendations greatly appreciated.

Adam

[Bill S.]

@Adam Olsen too much moisture, IMO is anything more than atmosphere. Where you are that means it should feel dry. If not, you have water coming into your structure which is bad. Lots of times wet basements are the result of poor exterior drainage. Poor exterior drainage comes from broken, missing, and bad gutters, improper grading around the exterior, and improper drainage onto the site.

Before you plan for drying out your basement you have to figure out what is the source of the water. There was one unit that I looked at that the gutters were bad and dumped all the water into a low spot which then literally flooded the cellar. Sometimes the fix is quick and surprisingly easy so your interior French drain would be a waste. That's just one example of why you must identify the source of the water.

If your problem is high ground water (rare in the West ), then really truly the correct solution is an EXTERIOR French Drain. Anything else (ie, interior French Drain) leaves the water against the concrete on the exterior which is bad for the concrete long term. I know people get by with less and I know companies that go around selling less but I don't consider them to be long term solutions even if they are cheaper and easier.