My concrete slab has no plumbing under it. It's an addition to the house (outside breezway turned into a room - between garage and house). House was built in 1940's in Michigan. We have a leak on the floor by the doorwall, only when it rains. Cannot see where the water is coming in. The carpet becomes satuated with water in a small area. HELP!

You have a water leak somewhere in the roof area where it obviously seeps into the actual outside wall and then down into the carpeting. Quite common condition. Carefully examine the roof area at the same location as the leak and then at least 10 feet on either side of where the leak is on the floor area. Also, you need to check further up on the roof as well for any damage to the roof shingles. It might not be an easy fix to find the leak but it's definitely coming from the roof and then down into the actual walls themselves. I had a similar type problem and only until I fixed the actual roof I kept having problems with water running or seeping down the insides of the walls in my home.