House in the hill

[bannerd]

With several kids now, the wife and I decided the small home we live in is no longer sufficient. So were going from a 700 sqft home to a 1600 plus a full basement. Otherwise it would just be 1600sqft. We always wanted to put a house on the hill near the pond. Since we have a 9ft slope, I decided to put a full basement in. I started excavating and it's all sand. When I dug down 3ft for the frost wall it was sand, more compact which is okay. Just that light sand you run into. When dried it's no good to work on.

How do you guys feel about pouring on sand? About 3ft down near the frost wall I thought I was hitting some rocks, but it was sand rocks. I back filled the area for now and will need to cut more out of the hill and grade the top. I'm going to pour either cobble or gravel but the core would be sand. Attached is the site, not much done as I don't get time to work on my own stuff, busy with others.

 

[DpSyChO]

Some people have horrible experience with their local building inspector but mine has been great. I've called him up several times prior to proceeding to the next step on my building to make sure how he wants it done. Sometimes he lets me know over the phone and other times he's said he would be in the area that day or a couple days later and would swing by if I wanted him to. I figure if I have not yet done that step, I'd rather find out if the way I planned on doing something would not pass BEFORE I do it. His job is to CYA so he will never tell me to proceed with something or or recommend less than what will meet code. Some may think it would be opening a can of worms by asking them to come out but how much $ and time are you willing to put into doing it only to find out it will not pass your local building code.

 

[Kaizen]

This is a good time for a soil analysis from a pro. building on sand without it is risky. you might need piers or I think they are called helicolumns to stabilize

 

[matt_i]

The best solution imo, for sub-soils that aren't excellent-bearing, is to increase the width and thickness of the pad at the bottom of the footing as well as add some perimeter-following rebars to it. What size were you intending on installing in your original plans?

You are probably going to have to excavate wider than intended, just due to the sand won't "hold a wall" the same as other soils.

 

[jives]

First, I cannot imagine that anywhere in upstate NY that 3' is deep enough for a footer and frost wall. Here in central NY it is 42" to 48". Second, generally you need to be on undisturbed soil for your footer, unless it is compacted properly. Meaning, you simply cannot lay down a few inches of gravel over the sand and call it good. If you are having these questions you REALLY need to talk to the local building inspector/code person. They are generally your friend, not your enemy. Time to do it right is now.

 

[bannerd]

The best solution imo, for sub-soils that aren't excellent-bearing, is to increase the width and thickness of the pad at the bottom of the footing as well as add some perimeter-following rebars to it. What size were you intending on installing in your original plans?

You are probably going to have to excavate wider than intended, just due to the sand won't "hold a wall" the same as other soils.

The footers will be 24" wide with 8" wall according to our contractor. Once the hole is dug, he wants it to sit for a year to settle.

 

[Cyberbear]

Building on sand has always been a risky choice, mostly avoided. Anything built thereon will be subject to future cracking and shifting of the structure, where doors don't close and windows won't open. I suppose if enough time, engineering and money is invested, anything can be done.

 

[LXCam]

What does your structural engineer say? or do you have one. At a minimum I'd spend the coin to have a soils engineering firm complete a survey for reference before going any further.

 

[bczygan]

Sit for a year???

Is that standard practice in your area?

How do builders ever finish a house?

Bill

 

[csp]

Threads like this make me glad that our local building department requires soils tests and engineered foundations based on the results of those tests. Takes the guesswork like letting it sit (seriously?) out of the equation.

 

[stanleyrleonard]

I watched the house in the attached video being built ["poured" is more like it] 27-28 years ago--started out as a simple sand hill--thought this would help with ideas--it is located @ 2001 Buckner Blvd in Dallas, Texas. Also, their exists three [3] UNDERGROUND homes in Plainview, Texas and one in Lubbock, Texas that were built back in the 70's--I always had an interest in pursuing the "UNDERGROUND/SIDE OF HILL IDEA" and alas, never took the first step--so I look forward to your build--Stan

Video:

 

[jives]

After re-reading it strikes me that you are only down 3', but will be going deeper for a full basement? What is down another 5 feet or so, at least on the uphill side? On the downhill side you you are still going to need to be 4 ft deep. Who knows, you may be at bedrock at 5 feet, meaning you simply have deeper frost walls.

 

[brownbagg]

sand is great for a building surface, I would say we do it all the time, well thats all we have is sand. so it not a unsuitable material by any means. just keep it confine. and sand likes water, a lot of water.

 

[wssix99]

+1 on consulting an engineer on this one. A local pro will probably know how far down you'll need to go to find solid soil. If you have deep sand, the most economical way to get a solid foundation is probably going to be to use piles.

BTW - VERY interesting mix of geology you have up there.

I ran into a 125 year old horse manure cespool under my planned foundation when we were building and I'm glad we called in the engineer. Things would have been very bad otherwise. (Sand is worse - but less "******.")

 

[theoldwizard1]

This is a good time for a soil analysis from a pro. building on sand without it is risky.

The best solution imo, for sub-soils that aren't excellent-bearing, is to increase the width and thickness of the pad at the bottom of the footing as well as add some perimeter-following rebars to it.

2 pieces of excellent advice.

 

[wssix99]

^ Spreading the footings out will deal with bearing but not compaction. Vibrations could cause the sand to compact and the house to settle. The local folks/pros should know how this is dealt with and if people usually dig deep and re-compact, do piles, do post tensioned foundations, etc.

 

[My Old Tools]

I watched the house in the attached video being built ["poured" is more like it] 27-28 years ago--started out as a simple sand hill--thought this would help with ideas--it is located @ 2001 Buckner Blvd in Dallas, Texas. Also, their exists three [3] UNDERGROUND homes in Plainview, Texas and one in Lubbock, Texas that were built back in the 70's--I always had an interest in pursuing the "UNDERGROUND/SIDE OF HILL IDEA" and alas, never took the first step--so I look forward to your build--Stan

Video:

Soil map of Dallas and my personal experience says that area of Buckner is blackland clay.

 

[stanleyrleonard]

Soil map of Dallas and my personal experience says that area of Buckner is blackland clay.

In addition, it is in a low lying area near the creek--so, my recollection has to be incorrect.