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Trucon01 08-01-2012 08:32 PM

How far under the basement slab is a typical footer?
3 Attachment(s)
I'm digging up the floor to put in some drainage and I'm already at 3 feet and still not to the footer????

concretemasonry 08-01-2012 08:50 PM

The minimum depth to the bottom of the footing is the local frost depth.

In some cases, it may be deeper if the excavator dug too deep or it was necessary to go deeper to get good soil bearing capacity. I have seen some that were almost 8' below the interior slab level.


Trucon01 08-01-2012 08:56 PM

Oh my god.... Why can't anything be easy? This weeping tile is not going to be the death of me...

Thanks for the quick response!

jomama45 08-01-2012 10:39 PM

Not sure why you're digging so deep for an interior draintlie, unless you plan to install and extremely deep sump crock.............

I take it these is a split level house or there's a partial exposure on this wall????

Trucon01 08-02-2012 11:43 AM

No, its a 3 story townhouse (2 stories above, 1 below). I had read everywhere that you should dig down to the footer, drill the blocks to relieve the pressure and lay the pipe next to the footer?

What is my best option at this point? I'm already 3 feet down and no footer.

oh'mike 08-02-2012 01:55 PM

Yikes---stop digging until you get an answer----the interior drains are there to relieve ground water pressure below the slab-- not to drain the outside of the foundation---

I'm not a foundation guy---wait for one to help---Mike----

jomama45 08-02-2012 10:42 PM

Ideally, the bottom of the interior draintile would be at least 12" below the top of the concrete basement floor. At 3' feet deep, you'll need at least a 4' deep sump crock to have any kind of storage between pump cycles.

As for how deep the footing might be, HERE in our environment it would be at just about 45-46" below the the top of floor in MOST common applications, but attempting to drain ground water that low would almost always be a losing battle........

Daniel Holzman 08-03-2012 08:27 AM

As previously stated, the purpose of drain tile is to keep your basement floor dry. The foundation could care less if it is dry, the tile IS NOT intended to dry out the foundation. Generally tile is put in about as Jomama indicated, typically about 12 inches below the slab level. Tile may be installed flat or with a slight pitch toward the sump. Tile can be installed outside the foundation wall or inside. You may want to review your project with someone who has successfully completed a similar project, I can't figure why you are going so deep.

Trucon01 08-15-2012 10:15 AM

This was just a test hole to see how far the footer was... I havn't dug anymore. If I only go 12" below the slab, should I still drill the blocks to relieve the pressure? I know the water would have to build up that high in the first place, but is it even worth it?


Trucon01 08-20-2012 10:29 AM

Any clue?

joecaption 08-20-2012 10:48 AM

Drilling hole is going to let water in not out.
While you have the foundation exposed I'd suggest applying water proofing foundation sealer up to the grade level.
It also will be a big help if you added fill around the foundation so there's a slight slope away from the foundation.

Trucon01 08-20-2012 11:17 AM

Hi Joe. The hole I dug is on the inside of the house, not outside... I was just wondering if I should drill those holes to allow the water in to the drain tile I'm about to install. That way the pressure wont build and seep through the walls.

joecaption 08-20-2012 11:23 AM

Why would you try to deal with the water after it's already made it's way through the block instead of preventing it on the outside?

Trucon01 08-20-2012 11:29 AM

I can't really afford 15k+ just for the excavation on the outside. Not to mention, there is no footer drains in this neighborhood to take the water away.

So I planned on installing a drain tile system next to the footer on the inside, but after I dug that hole, I found that its another 3.5 feet below the slab. So now I am asking, if I just put it a foot under the slab, what is the proper procedure.

concretemasonry 08-20-2012 12:46 PM

Joe -

He is trying to drain the soil under the slab and also provide foundation stability. He is also trying to drain the cores of the block to remove any moisture that could accumulate inside the cores (creating pressure to eliminate the water from the cores that has leaked through the exterior barrier, which is never perfect. The reduction of the hydrostatic pressure under the slab will also eliminate pressure cracks in the slab due to either from the exterior (outside the "footprint") or changes in water table under the home during the season.

In many areas, it is routine for good builders to install both interior and exterior drain pipe with plastic weeps as standard on every home during construction because of the low installation cost at that time. They usually provide pre-cut lengths of bulk 3/4" O.D. plastic/vinyl pipe to the mason contractors to install between the block and gravel around and under the drain tile. Usually, the mason contractor is responsible for the drain tile, bracing and backfilling since the basement slab is one of the last things poured (along with sidewalks and driveways).

This scheduling is done to allow the basement to be capped the day after the foundation is completed and interior utilities can be completed later whenever required. Very important when the foundation is built at 0F and the house must be enclosed and roofed in a few days with heat (the furnace is temporarily hung from the first floor joists) to allow interior finishing soon. This has caused the same process to be used in warm weather to minimize the effects heavy summer rains.


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