Hi Guys/Gals,
According to everything I’ve read on code and footings, you have to dig and pour footings on undisturbed earth/dirt. Well, the new Home Depot is being built on about 20-30 feet of fill. I’m pretty sure every HD I’ve been in has a concrete slab for a floor and I doubt their footings are 30 feet deep. I know that it’s compacted and such but it’s still fill. So my question is: What constitutes undisturbed earth?
The reason I bring this up is we(my wife) want to build a greenhouse on our property and half is on fill from my excavation about 20 years ago. While I know this is fill dirt, if someone bought this property and wanted to do the same, they wouldn’t know fill from original grade. We have a clay based soil (pretty much rock below 20″) that I’ve added plenty of organic material over the last twenty years. I’ve driven my front loader (7000 lbs +) over most of it so it’s compacted in this area.
Any reason I can’t just dig 8″ deep footers for this and be done?
Thanks,
NCtim
Replies
I can't just dig 8" deep footers for this and be done?
yes you can, a greenhouse has no weight to it, all the foundation is doing is anchor the greenhouse down.
as far as orignal dirt, thats a joke.
Haha! Thanks. I needed that. As for the weight, I guess I wasn't thinking outside the box there. Thanks.
"Undisturbed earth" is just that, undisturbed.
When they built that Home Depot they had an engineer come in, develop a plan, make sure the folks compacted the soil in the proper lifts with the proper machines at the proper moisture levels, and then tested to make sure they achieved a high enough compaction to make it acceptable for load carrying.
When I was building a shop a few years back the backhoe guy dug a little too deep on the footers and the building inspector made me fill with gravel and compact with a plate tamper OR I could hire an engineer and fix with dirt as above. Gravel and a tamper was WAY cheaper.
If you are concerned about the soil an engineer can test the compaction level. Running a loader over it doesn't necessarily make it properly compacted.
Steve.
had an engineer come in, develop a plan, make sure the folks compacted the soil in the proper lifts with the proper machines at the proper moisture levels, and then tested to make sure they achieved a high enough compaction to make it acceptable for load carrying.about the soil an engineer can test the compaction level. Thats me, super tester, soil, concrete, asphalt, subsoil, enviromental, piling.
""Undisturbed earth" is just that, undisturbed."Where can you find any of that?
Well, there is some under the new shop I just built in the corner of my horse pasture that has been a pasture for as long as my neighbor can remember. He is 72 and was born here.Which is why the shop is in the pasture and not nearer my house which would have required tearing out a bunch of very large trees to make room.Steve.
Thanks to everyone who responded. I think I'm going to study on this one for a while. I sure don't want a bunch of broken glass to deal with.
"According to everything I've read on code ...."
Don't know what Code applies in your locale, but the International Building Code 2000 explains all this rather completely and, for a Code, rather simply in Chapter 18. Section 1805 is specifically for "Footings and Foundations". Compacted Fill requirements are covered in Section 1803, allowable load bearing of soils is covered in Section 1804.
Edited 6/8/2006 10:34 am by Tim
"Well, there is some under the new shop I just built in the corner of my horse pasture that has been a pasture for as long as my neighbor can remember. He is 72 and was born here."But 72 years is a very short time period compared with the life of earth.I doubt that there is a spot on the earth that has NEVER BEEN DISTRURED (your words. Kansas was under the sea at one time and the Rocky's where flat beach front.I am looking for some time frame that is great than yeasterday, but less than ice age periods.
That's probably a good thing. Tearing out big trees leaves big roots under ground. When they rot out, they leave voids. Which is certainly disturbing if it happens under your foundation.
-- J.S.
Use to have have "Wise" Building Inspectors who would grab a #4 rebar and with all his weight press it into the ground. There were areas that the bar would sink a couple of feet into the ground, further deepening would reveal an old tash dump. Otherwise, he bar would penetrate only an inch or two. Now a lot of Inspector require a Soils Report no mater what.
Had a foundation guy who would probe the bottom of all his footings, he found a really soft spot. He digging reveal a seal trash bag, inside was a dead dog, as soon as the bag was opened, all the flies in the neighborhood came and a couple of guys started throwing up.
For a greenhouse it doesn't matter. If the foundation sink 6", the plants don't care and the floor will drain better.
As Steve said, undisturbed earth OR "engineered fill".
Of course, what the inspector doesn't know won't hurt him. May hurt you, but won't hurt him.
If there's glass in that greenhouse I would try to make it not move around too much. A great place for Information, Comraderie, and a sucker punch.
Remodeling Contractor just outside the Glass City.
Quittin' Time
Standard greenhouse construction (not a "sunroom" or whatever) mounts the glass very loosely in the frames. Considerable racking would be required to cause significant glass breakage.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
just post hole some pier below frost
I'm actually planning a three-foot block knee wall with old windows from the Habitat Salvage Store. The back end will be earth bermed up to the sill on block wall for heat conservation/tempering. 8 inches of pea gravel for the floor for drainage and heat retention. I'm thinking polycarbonate roof panels from Lowe's or a local lumber yard if they're competitive.
That's one reason I'm concerned about the earth under the footings. Too much shifting will definitely rack this structure, and I don't want to make mama mad.
NCtim
I wouldn't build anything more than a doghouse on 8" footers if you live in an area that gets frost. It's not that it'll sink -- just the opposite! Glass walls/ceilings want to be stabile.
Mike Hennessy
Pittsburgh, PA
Frost line is officially 6 inches here but I've rarely seen it go below 4. 8 inches deep is pretty standard here for garages and anything not bermed into a bank. It is the mountains, so flat land is hard to come by. Most everything is back filled to a point.
Edited 6/8/2006 4:50 pm ET by NCtim
Nice place, Fairview. I'm headed up to my grandmom's 92nd Saturday to crank ice cream - she's in Arbor Terrace now; she and Grandad's farm had a Fairview PO box since 1954. Sold a couple years ago to pay for the Terrace.
sigh -
Forrest
Glad she's got another birthday. Hate they had to sell the farm. Not many left except where I live.
Just checked the old address 333 Webb Creek Road, Fletcher, NC
Forrest
Beautiful out there.
Tim:
I think you got your answer about undistrubed earth. I too live in NC. The code minimum for footers anywhere in the sate is a minimum of 12" below finished grade. Mountanious areas require deeper. I tried looking up Fairview, but there are several of 'em according to mapqest. What county do you live in? I could probably look it up for you if you give me the county.
It sounds like you are buildig a structure with a foundation so you need real footers, unless the building is real small. What is the proposed size of the floor?
Hey Matt,
Every house I've built here (Buncombe County) the footings have always been below grade so I've never had a problem. This was more of discussion question because I get different answers from different engineers and the code is confusing. My green house is the first thing I've ever built that is partially on grade and I thought the answers were interesting. I've never dug less than a 16 inch deep footer for around here, buit I can get away with 8.
Well, the new Home Depot is being built on about 20-30 feet of fill.
Well, your greenhouse probably doesn't have a signed-off set of reports from a soils engineer, or xxx' of compacted, lime-stabilized fill (to picky engineer's specs) with a fully-engineered slab filled with all sorts of rebar, either.
Probably doesn't need any of that, either, your proposed greenhouse.
However, "undisturbed soil" is just that. The question them becomes, "Who's asking?" If it's the BI or the Permit Office, that could get a bit sticky. Now, twenty years is getting up there to where that's undisturbed--but, I'm just some dude on the 'net, too.
Hmm, I suppose you could sit the BI down with BT, and just finish the slab while he surfs . . . <g>
I live in an area that deals with that "undisturbed soil" situation on a daily basis.
For us, when we pour a slab, the load carrying beam section of the slab must be 12" deep, and REST on undisturbed soil. What this means is that the area that the rest of the slab sits on must be filled and packed to a depth of 12", then dug back out where the load carrying beam trenches are located, down to "undisturbed soil". If the land is grassy, then when the inspector comes out he better see grass at the bottom of your beam trench. If you dug too far, it's time to call in an engineer and get a compaction report.
If building a deck, and using deck blocks, the blocks must rest on undisturbed soil (area cannot be dug out). Same thing for cinder blocks used as support piers on pier and beam homes.
The rule is really kinda stupid, but most of the i local inpsectors are very gung ho about it.
By the way... we don't use gravel or crushed granite for a base. We use dirt... Go figure...
James DuHamel
He who dies with the most toys.... Still dies!
"For what will it profit a man if he gains the whole world, and loses his soul?" MARK 8:36
http://www.godsfreemusic.com
If the land is grassy, then when the inspector comes out he better see grass at the bottom of your beam trench. If you dug too far, it's time to call in an engineer and get a compaction report.
So they encourage building on top of organic matter???
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Yep. Never said any of it makes good sense, but that's the way it is around here.
My home is pier and beam, and based on the extremely large number of cracked slabs I have seen and dealt with over the years, I wouldn't live in a home around here built on a slab. James DuHamel
He who dies with the most toys.... Still dies!
"For what will it profit a man if he gains the whole world, and loses his soul?" MARK 8:36
http://www.godsfreemusic.com
I would agree, especially if they making people place those slabs on grass...We would get a failed inspection so fast if we didn't scrape the sod off first, I just can't believe there are areas that would be counter to general building practices.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
"We would get a failed inspection so fast if we didn't scrape the sod off first, I just can't believe there are areas that would be counter to general building practices."
See numerous other current threads about clueless petty bureaucrats...
Yeah, some are picky and others are not. As an update, I dug the footings yesterday and it took me 4 hours with a maddock and a shovel to get through the fill. The undisturbed dirt was like shoveling well rotted horse manure and I dug those footers in an hour, even though the total length was twice as long. Go figure.