Under Slab Vents with water in Northern US

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janszen

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Hi Everyone!

I'm new to the forum and I'm hoping someone can help me out with a issue I have been trying to find a solution to for a few years now.

Little back story..
I bought a split level home 3 years ago and when having the vents cleaned out we noticed water in the return vent (under slab below grade, lower level but not basement). Quite a bit of water.. Around 50+ gallons. I'v manage to drain it a few times using a we shopvac. But it fills up quickly after a rain.

Forward one year, I determined it had something to do with the drain tile. I replaced the drain tile around the house where the issue was. All seemed good until the next rain and the vent filled right back up. After talking with a few contractors we came to the conclusion that the return vent is actually lower than the footer. Making the drain tile ineffective when preventing water from entering the vent.

I believe my only option is to repair the vents under the slab. I think the only one that needs fully repaired is the return. One idea I have is to cut a channel in the slab and install two 4" PVC pipes and backfill with concrete. Eliminating the standing water in the vent and sealing them off completely from the ground. Good idea or not?

I have also though about running new vents overhead but there just isn't any room.

Attached are some images of the layout.

Any help or ideas would be greatly appreciated!

lowerlevel-basement.jpg

side-view.png
 
Will the 4" meet the volumetric requirements of the existing return air and is it your plan to manifold the PVC to the ducting beyond the elbow?
 
Do you have down spouts feeding the same drain system?
I think if you seal that area the water will just find the next spot.
How much lower is the basement?
 
Will the 4" meet the volumetric requirements of the existing return air and is it your plan to manifold the PVC to the ducting beyond the elbow?
Yes it should, it will at least be better than what air flow there is now.. Currently the vent is 50-70% filled with water. I only have two return vents upstairs that the duct feeds.

Do you have down spouts feeding the same drain system?
I think if you seal that area the water will just find the next spot.
How much lower is the basement?
No I do not, they are all piped above ground about 4ft away from the foundation. With proper grading away from the house also.
The basement is around 5ft deeper than the lower level slab. I have never noticed any water issues in the basement.
The water does only raise up to a certain level (50-70%) and does drain off into the sump eventually.. not sure how but I've used tracing dye and it does.
With the return vent where the water is being the lowest spot, I'm not sure where else it could go.
 
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I just hate to see someone having to cut an otherwise clean slab.

Have you had an xray performed to determine the exact location of the ducting, as well as what method of reinforcing was used in the slab?
 
I just hate to see someone having to cut an otherwise clean slab.

Have you had an xray performed to determine the exact location of the ducting, as well as what method of reinforcing was used in the slab?

I agree with you..

I have not but I'm 99% sure where the duct goes from visual inspection and cameras. I do not know what the method or reinforcing the slab is. The house was build in the mi 1960s. I don't think its per-stressed concrete. Are there any ways to determine this?
 
You may be able to determine the reinforcing method, if any, by visiting your building dept. Some will retain the plans on microfilm. Other than that, an xray.

A prestressed or post tensioning slab will be conspicuously marked, generally within a garage.

If there is reinforcing, you'l need to provide sufficient space between the cuts to recreate it, and rebar laps at 24 bar diameters.
 
What size is the duct below the floor?
What is your access to it?

I know you have thought about re routing it but I would like to look at that.
Do you have open access to the duct work in the basement

Is the basement finished?
What are the rooms in the lower used for?

I would also put temporary extensions on the down spouts to get the water further away from the house.

Where is the sump located?
 
What size is the duct below the floor?
What is your access to it?

I know you have thought about re routing it but I would like to look at that.
Do you have open access to the duct work in the basement

Is the basement finished?
What are the rooms in the lower used for?

I would also put temporary extensions on the down spouts to get the water further away from the house.

Where is the sump located?

There are two trunk lines that run from the basement to under the slab that I have access holes cut in. They are about 8" x 18" each.

Basement is not finished, One side is a office and the other is a living room.

Sump is located in the basement furthest corner from the stairs.
 
Where I live these under slab deals are a thing of the past and believe there is always a way to run ducts.

The ceiling joists run from the outside wall to the center wall, yes?
How much distance between the ceiling and the windows in that outside wall?
 
Where I live these under slab deals are a thing of the past and believe there is always a way to run ducts.

The ceiling joists run from the outside wall to the center wall, yes?
How much distance between the ceiling and the windows in that outside wall?

Yes the joists run from an outside wall to the center.

There's only 3-4inches above the windows.
 
Yes the joists run from an outside wall to the center.

There's only 3-4inches above the windows.

Can you sketch in the placement of the windows.

The height of the ceiling, the height of the passage to the next room on that floor.
The height of the opening for the stairs, if those stairs are leading to the basement.
 
ceiling height is 7ft.
height of passage over the block wall is 10"

Updated pictures.

p1.jpg

p2.png
 
Sorry, I assumed the center wall was a stud wall with a space to bring return from upstairs.
So where is the return air vent for that floor?
How did they get the heat ducts into the ceiling?
At the staircase up check the thickness of the floor above. from the lower ceiling to the upper floor should be about 11 inches.
 
the return vent for that floor is the same one that goes upstairs. just using the gap between studs to go upstairs and a opening at the bottom for that floor.

Heat ducts make it to the ceiling by going underground to the block wall then in between studs again to the upper level.

That is correct its about 11", but that floor has vaulted ceilings above the basement. No attic to go to.
 
Min. ceiling height is 80" and 3.5 inch rectangular duct are available off the shelf and smaller can be made. You could come across the bathroom with a drop and in the closet have access to a bay between ceiling joist and move the return vents up and down to that wall space at the center wall.

After that I think I am might be out of ideas.:)
 
If you were looking at the drop thru the bathroom, return air does not need a duct so 2 2x4s and a chunk of drywall.
 

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