What I'm Seeing Now


When HVAC Ducts Run Under The House

When HVAC ducts run under the house.

What?  Ducts that run under a slab?  Ducts that run underground? 

That was very common in the 60s and 70s in Virginia.

Can that be a problem?

Yes.  Such duct work can break down over time and deteriorate.

This house was built with a ground-level slab.  The HVAC duct work for the lower level ran entirely under the slab - entirely underground. 

As such, and if deterioration occurs, the duct work can fill up with water and mud, and even various sorts of animalia that can get inside.

I have seen ducts fill with tree roots!

When full of water, if/when the heat or AC is running the water in the duct work itself will contribute huge amounts of moisture to the house.  And that moisture can be laden with whatever microbial contribution that is amplifying inside the ducts!

Water staining can be seen in this particular duct and water has obviously sat in there in the past.  And where did this mud and detritus come from?

Obviously such this duct work technique is not done anymore, at least in my area.

Can the deteriorating condition of underground duct work be remedied?

Again, yes.  There are spray techniques that can coat and recondition underground ducts that have deteriorated or have filled with mud and moisture, and even molds.

My recommendation:  sometimes when you buy an older house you will find techniques and products that are no longer done or used.   Usually there are reasons for that!   This is one technique that is rife with the potential for future problems, which can develop quickly or over time.  And once such problems begin they don't simply stop or correct themselves.  When problems develop a remedy might be considered - and should be considered sooner rather than later.



Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560


Comment balloon 13 commentsJay Markanich • March 18 2017 11:10AM
When HVAC Ducts Run Under The House
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