foundation near a slope

[devildog]

 I wanted to run  this by the CP forum to see if anyone had any  idea what the setback is. I understand it might be different for each state, but I didnt know it could be a problem till yesterday.

While meeting with 2 different general contractors yesterday, they both mentioned that I had more than a 45 degree slope and that the building inspector would have to look at it and give his approval or I'd have to move the foundation back a little. I also heard the word "engineering" in there somewhere.

The problem with this is, that Ive also got to stay 10' away from the septic, and im already pushing it.

Also , could anyone tell me what part of the septic ststem I need to stay away from? Is it all of it? The tank? Drainfield?


Its hard to tell from the pic,but on the righr side of pic it drops off really hard.
thanks for any info you might have, Darrell

[glenn kangiser]

Around here they make you stay off of fill or get a compaction test, but I have seen houses on pretty good stilts - using proper building techniques - of course.  Wouldn't hurt to ask the inspector his opinion either though if you will be dealing with him anyway.

I think it's minimum 5' from the tank and farther from the leach lines.

[diyfrank]

Sounds like he's talking about the angle of repose. You need to be a 1 to 1. For every ft down you need to be a ft away.  If the bottom of your footing is lets say 3 ft deep and there's a drop off next to it, that drops 10 ft the bottom of your footing needs to be no closer than 7 ft from the drop off.   If that's not possible you can have a geotech look at it, and if he determines the soil will support the load with less than a 1 to 1 and gives you a report to show than you should be good to go.
You can google angle of repose for more info.

[Don_P]

Section 403.1.7 is worth reviewing;
https://www2.iccsafe.org/states/Virginia/Residential/PDFs/Chapter%204_Foundations.pdf

[John Raabe]

You can do just about anything with enough engineering - but soil testing and the resulting engineering work can be very $$$$$!

Ask for a site visit with the inspector before you get too far into this.

A client had a nice view site in Seattle where they spent $2.5k to find out that they could spend their entire project budget on retaining walls and compacted fill. They sold that lot and built elsewhere.

[waggin]

Are you sure they said 45 DEGREES and not 45 PERCENT?  45 degrees would be a 1:1 rise to run, or a 100% slope.  From your picture, it sure doesn't look like it's a 45 degree slope.  For comparison, look at some of the projects on here where people have a 12/12 roof.  That's a 45 degree slope or 100%.  I can't imagine any building dep't allowing building on that unless it's basically solid granite.  45% would equal 24.2 degrees.

My jurisdiction has a 50' setback plus a 15' building setback, a fancy way of saying 65' total from anything 40% or more slope, which is about 22 degrees.  To build closer, you have to have a geotechnical study done.  With that, my county will probably allow me to be within about 30-35' from my slope, which is just over 40 percent.  That's based on a neighbor's approval.  For my lot, I've been quoted around $3k for the study, and I'll probably do it to best situate buildings in a limited area.

See this link for a table on converting slope measurements:

http://www.greenbeltconsulting.com/articles/relationships.html

As others have mentioned, setbacks from septic components vary depending on what part of the system you're talking about.  Setbacks from tanks, lines & pumps are probably minimal, but from drainfields, it's more critical, plus an additional factor if you're cutting into a grade.  So if you'd be cutting into grade, you'd probably have to add an additional x' of distance to your 10' setback for every y' of cut depth.

[devildog]

Thanks to all who responded. The building dept. was closed today. Ill try again tomorrow.
I  never considered, or even thought that this would be an issue,but I dont want any additional costs. So if he tells me to move it back, then I guess thats what Ill do.Its very dissapointing though. From the beginning, thats where I wanted it. Maybe he'll say its O.K.
waggin, I dont remember now if it was 45 deg. or 45%, but it is pretty steep.

http://www1.snapfish.com/thumbnailshare/AlbumID=242066705/a=10226827_10226827/t_=10226827
some of these pics show how steep

[diyfrank]

Ya its steep.
It doesn't look too steep from a structural point . your county may have some requirements that prevent building too close tho.
What type of foundation are you planning to go with? 
As long as your footing is deep enough on the drop off side to get your angle you should be fine.
Ive put in a number of foundation that look to be hanging off cliffs but they maintain the correct angle.
A lot of the lot jobs we do are 5' off the property line. Then a rockery that drops 4' to the next lot, and so on.

[devildog]

I talked with the building inspector today. The info that Don P added was exactly what he said.
So, what I have to do is measure down 18"(frost depth) from top ofslope, and then measure from that point to the bottom of slope and divide by 3. And that is how far back my foundation has to set back from drop off( top of slope). so 60' down slope  would be 20' setback. Im going back in 2 weeks to measure and reset stakes.
The building inspector said that the foundation had to be 10' from septic tank only, the drainfield doesnt matter. its because the pressure of the foundation could cause the tank to cave in.
Darrell

diyfrank you posted while I was typing. Its a crawlspace