Sometimes on a slab home, or a home with a lower level that opens up on the rear, I see the duct work running downward from the HVAC system to service the house.
I point out to my clients that ducts under a slab will very often be an issue.
The system seen here services every room on the lower level of this house. That is the supply duct visible on the left.
Every single register except one blows the air from the floor.
Personally I don't like floor registers even on upper levels because I find them less efficient during air conditioning and they always affect furniture placement. It seems that the registers are put into a room right where you would want the bureau to go! But that is just me.
But aside from that, what's wrong with ducts under a slab?
Many things can result. Among them are:
1. They are inaccessible. If anything goes wrong with them repairs can be difficult and/or expensive.
2. When the heat is operating those ducts are cool. Their temperature varies little. Condensation results. I have seen ducts blowing from under a slab onto a wall which is wet with condensation. People have called me out of the blue, after finding me online, to ask why their walls are wet!
3. The ducts are metal. Metal rusts. This duct is not rusting much yet. But you can see the pitting. Actually it is much better than I expected! Is the rust and pitting worse where the opening is not exposed to drier air?
4. As the duct rusts, it can open up.
- I have seen ducts under a slab that have a couple of inches of water in them from the water table outdoors!
- I have seen ducts full of mud!
- I have seen dead snakes, turtles and frogs inside ducts! No kidding here either.
- I have seen ducts that have completely disappeared and what is left is part slab and part soil!
- Sometimes as the lower duct material disappears, the soil level can raise as water deposits more material, effectively closing off the duct and creating a half moon of service. THIS IS EXTREMELY INEFFICIENT.
- I have seen ducts full of molds, fungus and even mushrooms. As they say, all manner of microbial growth! Can you spell H-E-A-L-T-H-F-U-L boys and girls?
Of course the problem worsens as the house ages.
My recommendation: even on new construction, if you have a property with ducts under the slab, have a peek. See what they are doing. But mention it to your clients. Physics have principles that are always obeyed unless they are overcome. When heat and cold mix, moisture results. Pure and simple. Unless something is in place to control that moisture, water will do what water does.
AND WATER IS THE KILLER OF HOUSES.
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560