I have a question about filling in under a foundation.  The dirt under the rear of my mothers  house has dropped quite significantly and she has not done anything about it.  I am trying to help her fix it before it gets really bad. What type of soil/sand should I use?  Topsoil with cushion sand underneath or just topsoil? I have no idea about any of this but I know that there should be dirt up to about 4-5" below the top of the foundation and slope gradually away from the house (or higher the closer towards the house).

They live on a creek lot and I swear they loose a foot of land a year from erosion.  The back of the house is built up 6 feet and railroad ties are stacked at the edge.  There is a deck built out over the railroad ties that used to be level with the house.  From wood shrinkage and whatever else the deck is now 4" below the ties.  Her foundation is hanging out in space and there is no dirt under it all across the rear of the house.  The house was built in 98 and I noticed this a month ago.  There is a flower bed with plants in between the foundation and the railroad ties which are about 4 feet away from the foundation.  

I live far away so I do not have pictures but I can go get some if I need to. Thanks for your help.

If you are loosing support under a foundation gravel is about the only acceptable thing.

If you are just looking for fill that is not going to bear weight you can use whatever you want.

Loosing support under a foundation is  BIG deal.
They are rarely designed for anything but almost 100% support, and cracks and shifting often quickly follow any significant loss of support.

I would fill in with concrete, gravel can wash out too.

Quoted: Quoted: I would fill in with concrete, gravel can wash out too. And get a professional to do it--the house is in grave danger of being destroyed, and this is not something that will be remedied by throwing a few shovel fulls of dirt at it.   If this house was built in 1998 instead of 1898, then someone has screwed up royally by allowing this to happen.

Yes 1998 - she is a 62 year old woman and clueless about homes/cars etc.  She was asking me about it because her flower bed dropped.  That is when I went outside to look at it. It is just the edge but it is a definite emergency situation.  I don't think it was constructed properly. There is still dirt under the foundation but you can see where the foundation stops.  So concrete should be poured there?  What is to stop this from happening again? I will get some pics as I am going over there Tuesday.  

Foundations are often built on undisturbed soil.
The load bearing rating of soil varies with type, and the footer width is adjusted to hold the calculated load from the building.

Even putting concrete under a foundation that is subject to flowing water will not do very much good.
The force of the water will simply erode the soil under the new concrete.

You will probably need a geotechnical engineer to figure out a way to protect the foundation if moving water is that close.

You also will quickly get into EPA issues with putting fill in (or even near) a stream.

people that want beach/river front property ususally get what they want.  mother nature will make sure of that and you wont be able to hold it back.

there are PROFESSIONAL companies that will jack up the house, but im not aware of anyone doing the foundation.

i would look to move the house.

Quoted: Foundations are often built on undisturbed soil. The load bearing rating of soil varies with type, and the footer width is adjusted to hold the calculated load from the building. Even putting concrete under a foundation that is subject to flowing water will not do very much good. The force of the water will simply erode the soil under the new concrete. You will probably need a geotechnical engineer to figure out a way to protect the foundation if moving water is that close. You also will quickly get into EPA issues with putting fill in (or even near) a stream.

The creek is about 80 yards behind the house.  It is a normal subdivision with 15 houses that back up to this creek.  The problem is there are no gutters and the water comes right off the roof into the flower bed. She is getting gutters now too.  There is not a water problem except for the fact there were no gutters.

Quoted: Quoted: Foundations are often built on undisturbed soil. The load bearing rating of soil varies with type, and the footer width is adjusted to hold the calculated load from the building. Even putting concrete under a foundation that is subject to flowing water will not do very much good. The force of the water will simply erode the soil under the new concrete. You will probably need a geotechnical engineer to figure out a way to protect the foundation if moving water is that close. You also will quickly get into EPA issues with putting fill in (or even near) a stream. The creek is about 80 yards behind the house.  It is a normal subdivision with 15 houses that back up to this creek.  The problem is there are no gutters and the water comes right off the roof into the flower bed. She is getting gutters now too.  There is not a water problem except for the fact there were no gutters.

All you need is packed gravel (even pea gravel) and to make sure erosion has been arrested.
Absent flowing water there should be no further issues.

I have dealt with lots of undermined foundations and i have never seen one get approval around here for just backfilling with gravel.  We always specified lean concrete for undermined foundations and over-excavations.

OK, had 2 foundation guys come out - 2 different companies.  They both said it was no big deal that the pears they put in the foundation made it incredibly strong.  They both said to simply add soil to 4" from the top of the foundation and to install gutters.  They both suggested to replace the retaining wall in the rear but said the foundation was fine.  There was a slight slope but said that it did not need anything to be done.  So I am going to get some pea gravel then a ton of dirt.  My mom will have someone come redo the retaining wall and install gutters and hopefully all will be good.

Thanks for everyones advice and suggestions.  I will get some pics before I start adding the gravel and soil.