Chimney Footing is very shallow.

[fufu]

Hi there.

I'm replacing the perimeter drain on one side of my home. The drain goes under the chimney. As you can see from the images (below), it looks like the footing under the chimney is only about 3” thick. I haven’t actually dug under to see if there’s anything else under there for fear of bringing the thing down. When I poke around with a screw driver, it goes right into dirt (heavy clay).

I’m not sure what to do now. I can’t replace the drain without digging the dirt out from under there, and I’m pretty sure I can’t dig under there without the chimney falling over. Any suggestions on how to support the footing? I think I’d like to pour a new footing if possible.

Any suggestions would be appreciated.

Thanks.

[pushkins]

Digging under a footing like a chimney footing is not for the faint of heart and should only ever be done by someone experienced in footings and or pining of footings.
I'd be surprised if the footing for the chimney was only 3" thick that chimney looks to be around 20' in height therefor amassing a reasonable amount of weight, a 3" footing on clay would have shown signs of problems like settling and or cracking. Having said that I have had the occasion to see much less footings on much greater structures and not a crack or settlement to be noted, (gotta be lucky sometimes I guess).

If it were me I'd divert my new perimeter drain around the chimney , it's not that greater extra distance and in the long run will save you a considerable amount of time and money if you upset the chimney footings.

[fufu]

I've added some text to the following image that I hope will help explain the problem a bit better. I have a couple questions as well.

I've poked a rod under the footing (which is actually 4 inches thick), and it goes right under there. There's nothing but wet organic clay soil.

So, if you look at the picture that has the whole side of the house and the chimney in it… there’s a door that leads into the basement right behind the chimney. Its right at the base of that door - in the corner closest to the chimney – that water is leaking into the basement.

If I install the drain around the chimney, will I solve the problem of water leaking into the basement?

Also, the drain pipe that runs under the chimney is the old red clay type (the drain tile has been replaced once, but they didn’t touch the part that goes under the chimney). I’m a bit worried that if I leave that old drain tile under there, it’s only a matter of time before the soil under that 4 inch slab settles and brings the thing down.

What can I do?

Here's the image.

[pushkins]

Wow ....4" footer!!!! Like I said I've seen less and they are still sound and stable structures.

Your right not to be fooling around with he 4" chimney footer, problem with situations like yours, is the whole chimney could come down if you mess too much with it and you can imagine that cost !!!!

If you dig out at the basement door where the leak is and seal that wall below grade with foundation sealer and possibly rubber membrane if you really want to do a good job, then divert your perimeter drain around the chimney making sure you grade around the wall toward the perimeter drain and backfill with gravel/rock. (Make sure you cut completely the old perimeter tile under the chimney so no water can run back into it, spray foam works a treat to seal it up).

If you want you could "sleeve" the clay tile that is under the chimney and connect either end to you "new" perimeter drain.
For example the clay tile is a 4" diameter then insert a 3" sleeve of PVC inside the clay tile and reduce and increase either end to match you new perimeter drain. Example = 4" perimeter drain pipe reduced to 3" under chimney sleeve pipe increased back to 4" perimeter drain pipe on the other side.
There is no high pressure involved with perimeter drains so this small reduction over about three feet and then increase wouldn't pose a problem.

This latter option would be my pick, but I'd still foundation seal the leaking section none the less after all, your going to have it dug out anyway.