In slab ducts

Looks to me that the ducts were half full of water at one time.

Is the cracking of the ducts a concern? It seemed to be at the top portion. Is this from when they break them for the floor registers?

I have some verbiage that states: In slab ducts are subject to, and prone to water intrusion

Are those clay tile David?

I’ve seen under slab ducts made of of transite(asbestos) and plastic.


Yes they are clay.

I think your observation about being half full of water at one time is valid.

I also wonder how the tile you can’t see looks

Any under slab water will end up is those ducts so site drainage is of paramount importance.

Write it up and disclaim what you can’t see.

Sub-slab duct systems are nearly always a problem and the only reason I use the word “nearly” is because I am holding out for finding ONE that did not have problems. I don’t think I have seen a one that either did not have water in them or have water stains showing that water had been in them. I have seen clay tiles used for these ducts, as in the photo. Even if the contractor wraps them in plastic, as I have seen, they still leak.

Further, leaks in the ducts can be a route for soil gases to enter the home, especially if the duct is a return. If the area has radon problems, such soil gases can be a serious problem. In that case, I am thinking that the only resolution would be to install new duct work.

Now, maybe someone has observed a subslab system that doesn’t have problems, and maybe if the home is built high enough above grade, it might not at least have leak problems. But, I see no way to avoid soil gas migration problems, unless the fan is run constantly and the ducts are on the supply side.