I am submitting my drawings for approval this week for my cob house here in Chemung NY. I just was told by our code enforcer that I will need a cement footer under the stone walls.....I am building a stone basement (walk out) under my cob house
How do I incorporate the rubble trench with a cement footer?
Thanks for all your help Permies peoples without it I would not have come this far! If my drawings are approved I will be digging next week, I promise pictures soon! So excited but so busy!
Not being a building inspector in NY, I'd suggest, dig the footer, put whatever steel into it that is required, pour the cement, then while the cement is still wet, set the first layer of rubble into the footing...
Sorry you have to go through such silliness. If I am not mistaken you are not far from Ithaca and the PA border...correct?
You might try suggesting politely to the "code enforcer," that "concrete is not how most of the Older and very well built traditional homes in your area are designed and built. I would further share with them..."nicely"...that these structures are enduring the decades that age them...much better...than many modern homes. "Gravel trench" foundations..."do not" actually require cement footers at all in most areas, and if they (code enforcer) could, "be so kind" as to show you where in the local building codes it states this is required for a "tectonic or compacted gravel foundation, to have cement added to the format of the build?" You will need large "sill stones" and/or a very strong concrete mix, which is never as strong as stone itself, until you get into some of the "geopolymers" which I don't think there are any suppliers in your area yet, unless there are in Ithaca now.
It may pay to have a PE look at and sign off on your designs as this will "supersede" the "code enforcers" authority in almost every example I have ever experienced here in America. In most cases they (code enforcers) try to "bully" folks into building a structure the way "they understand it should be done" and/or the way they "interpret code." A PE stamp takes care of this very swiftly and gives you the peace of mind that your design is solid. If you go this route, do find one that understand traditional building, and that can be a challenge in some areas.
Also, if you just "give in" to them and agree to pour concrete you will need a: "high early strength OPC fiber reinforced concrete footers"...
General Format for Gravel trench/pad for stone walls:
The format with or without concrete is typically to dig down to the level you are building your "walk our stone cellar" under the house and go approximately an additional 600 mm (~2 feet) beyond that point.
Now you should also be installing all your drainage trenches at this time with the proper filter cloth if that is part of the design.
The "concrete footers" (if they "have to be" part of the system) need to extend 300 mm (~1 foot) past the outer edges of the intended stone wall base thickness, and should be about a 12" thick (with 16" being much better.)
In your case I am assuming that the base of the stone wall is about 800 mm to 1 meter (~2.5' to 3') wide and having a good outward "batter."
The top of the wall I presume is approximately (~1 foot) wide for a 2.4 meter (~8 foot) high wall, with about 500 mm (~20") or so extending above finished grade. This can vary, but without you blueprints in hand I can not give more basic feedback than that.
Now the area, before gravel is "placed" not just "poured" should be level and clean mineral soils with all the drainage properly laid out.
The first lifts (layer) of stone/gravel should be 50 mm (~2") crushed stone in two 200 mm (~8") "lifts" (aka layers) to start this process. Some folks are now adding "geotextiles" before the gravel and between the lifts to add stability to the matrix of stone. Note: some PE require this.
Compacting traditionally was done with a "stump pile driver" but today you can rent a "plate compactor" that should run over each lift...8 times.
A final "half lift" can be laid with 20mm (~3/4) clean crushed stone (not "hard pack" which is stone with "stone dust added.") This too must be properly "tectonically stabilized" (aka compacted.)
This final layer s is where your "form work" will start for the..."high early strength OPC fiber reinforced concrete footers." This "form work" can be simple slab boards well laid out, and squared. The forms should be well staked and supported against collapse from the pressure of the poure, and with good "mold release" applied to the wood so the concrete doesn't stick to the boards. This can be a "beeswax wash" or a just paper lining, however the suppliers for the concrete will have their choice, and should be able to do the form work properly...For a fee.
I hope that covered the basics, and I am glad to offer more assistance where I am able.
I am sorry that your Uncle was not successful (or better equipped perhaps as a DIYer...) to achieve his goal of building with an all stone foundation. This can take place if the builder/DIYer is not fully versed in "stone work"...be that "dry laid" modalities or with different mortar laid methods like the common "Ashlar" or they less common, but more tectonically stable method of "herringbone."
I must share with all the reader of this post that taking "anything" off the "internet"...without vetting the information with someone accomplished in a given skill set...is always a "risky venture," and not advised. I further would not take the "ConcreteNetwork.com" as a very good sorce for a "complete concideration" of fondations. It definitely is not one to reference even a little bit if trying to build a "stone foundation," as the information is "biased" and very limited in scope.
Sorry Li, but that is not a link I would ever offer to clients or students in outlining methods for any type of "traditional or natural" foundation, and only limit its advice to the very narrow scope of OPC concretes, which of themselves, OPC has more pitfalls than positives in the building arts. I am currently corresponding with several Historical Building Professionals in the U.K. that are suffering all types of "ill effects" from the "over use" of OPC mortars, plasters/renders, and related applications of concrete. This material has actually a very limited context of application, and most modern forms are but pale shadows of the "natural cements" and/or "Roman Cements" and historic pozzolanic or "geopolymer" mixes.
Jay is correct, IRC/IBC CH 4 international code does not require a footer under a rubble trench. This jurisdiction must be making up their own rules for single story building's. A footer under a rubble trench makes drainage more difficult. If the building is 2+ stories code requires a spread footer. When it comes to ANY foundation getting loads to the ground the wider the footprint to the ground wins! There are ALOT of factors that can cause a home to tilt, if it does that is a good indication the design was bad to begin with....IE: Designer did not understand the properties of the soil (no soil test), foundation material, inaccurate stress Engineering, poor drainage.