# Under Slab Vents with water in Northern US



## janszen (Oct 26, 2016)

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!


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## Snoonyb (Oct 26, 2016)

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?


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## nealtw (Oct 26, 2016)

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?


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## janszen (Oct 27, 2016)

Snoonyb said:


> 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.



nealtw said:


> 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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## Snoonyb (Oct 27, 2016)

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?


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## janszen (Oct 27, 2016)

Snoonyb said:


> 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?


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## Snoonyb (Oct 27, 2016)

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.


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## nealtw (Oct 27, 2016)

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?


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## nealtw (Oct 27, 2016)

I have been reading this site.
There preferred fix is re routing.
http://inspectapedia.com/aircond/Ducts_in_Slabs.php


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## janszen (Oct 27, 2016)

nealtw said:


> 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.
> ...



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.


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## janszen (Oct 27, 2016)

nealtw said:


> I have been reading this site.
> There preferred fix is re routing.
> http://inspectapedia.com/aircond/Ducts_in_Slabs.php



I have read through this site also, I don't think I have any room to re run the ducts. There isn't really any way to get to the ceiling from the trunk lines.


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## nealtw (Oct 27, 2016)

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?


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## janszen (Oct 27, 2016)

nealtw said:


> 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.


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## nealtw (Oct 27, 2016)

janszen said:


> 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.


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## janszen (Oct 27, 2016)

ceiling height is 7ft.
height of passage over the block wall is 10"

Updated pictures.


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## nealtw (Oct 27, 2016)

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.


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## janszen (Oct 27, 2016)

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.


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## janszen (Oct 27, 2016)

Couple of picture that may help


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## nealtw (Oct 27, 2016)

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.


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## nealtw (Oct 28, 2016)

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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## nealtw (Oct 28, 2016)

I was wondering why you had a 7 ft ceiling, my guess is the city made them raise the floor to keep the heat ducts above the drain tile.
If they knew he was going deeper they would have called for it to have it's own weeping tile system. Somebody cheated.


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## Snoonyb (Oct 28, 2016)

nealtw said:


> I was wondering why you had a 7 ft ceiling, my guess is the city made them raise the floor to keep the heat ducts above the drain tile.
> If they knew he was going deeper they would have called for it to have it's own weeping tile system. Somebody cheated.



From the Seattle residential building code;1208.2 Minimum ceiling heights. Occupiable spaces, habitable spaces and corridors shall have
2 a ceiling height of not less than 7 feet 6 inches (2286 mm). Bathrooms, toilet rooms, kitchens,3 storage rooms and laundry rooms shall have a ceiling height of not less than 7 feet (2134 mm).


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## nealtw (Oct 28, 2016)

Snoonyb said:


> From the Seattle residential building code;1208.2 Minimum ceiling heights. Occupiable spaces, habitable spaces and corridors shall have
> 2 a ceiling height of not less than 7 feet 6 inches (2286 mm). Bathrooms, toilet rooms, kitchens,3 storage rooms and laundry rooms shall have a ceiling height of not less than 7 feet (2134 mm).



Yes that is the new code but there are acceptations for beams and such and they can be 78"

Up here they still use 80" for doors, stairs and drops.
http://www.doityourself.com/stry/explaining-ceiling-heights-under-the-international-building-code


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## nealtw (Oct 28, 2016)

If I was going to dig it up and repair it I would also consider drainage.
Drain tile around the duct and change to solid pipe, straight out the front under the footing, two feet away from the footing turn and tie into the drain near the front porch.
I would do most in solid pipe so you are not changing the moisture content of the dirt supporting the footing.


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