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Cob foundation

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posted 2 years ago

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So this may be a dumb question, because I can't seem to find an answer anywhere.... We were planning on building a small roughly 1,200sf house/greenhouse. The front (north) wall is going to be a cement block based bottle wall using concrete. This wall will also be wrapping the sides for 12' of the 30' side walls. The back (south) wall will be an earth packed tire wall. The sides were planned to be pure cob. With brick and earthen floors. The concern is whether or not I need foundation/footers with it being on a slightly sloped clay bed (over all slope of 8" over a 40' distance) with a 2'x2' drainage ditch all the way around it and a 3' over hang planned for roof? If it matters we are located in South MS. Pretty dry except for a couple of non-consecutive months outta the year

Matt McSpadden

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Location: Central Maine (Zone 5a)

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posted 2 years ago

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Hi Kimberly,
There are some great builders here. I am not one of them :), but in my experience, every building needs some kind of foundation if it is to last. The size and materials may change based on geography. I would imagine you are going to want something.

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Kimberly Gainey

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posted 2 years ago

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Thanks. I was unsure if laying a brick and mortar floor would suffice for foundation in place of a solid slab. First attempt at building a cob/recycled building and all the conventional ones I've been a part of were built above ground lvl on blocks or "stilts". Don't want to put in all the labor only to have it collapse in 5yrs hahaha. Especially when I've heard of cob buildings lasting thousands of years.

Matt McSpadden

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Location: Central Maine (Zone 5a)

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posted 2 years ago

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In a very dry environment, I imagine you could probably get away with it. I would be worried though, about having two different materials making up the walls, that it would need something underneath to tie it all together so you don't get shifting and settling at different rates.

Kimberly Gainey

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posted 2 years ago

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That is a very valid point.... i didn't consider the weight difference in material for the walls in relation to settling. My main focus was on load bearing not the weight of the walls themselves....Sigh... I guess atleast footers would be smart. I would really like to avoid so much concrete as a slab though if feasible.

Matt McSpadden

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Posts: 2191

Location: Central Maine (Zone 5a)

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posted 2 years ago

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You could probably do what we call in the north a "frost wall"... I'm not sure what they would be called down south :)

It's just where you build a foundation around the edges of the building to hold the wall, and the middle is either left as dirt, or as a really thin cement slab.

Kimberly Gainey

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posted 2 years ago

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Thanks Matt! I didn't consider that. Lived in CO for a few years, but that has been over a decade ago. I forgot that was even a thing! Will definitely look into that option as well. Was researching rubble trenches and stone foundations, but the latter seems really intimidating without professional help haha.

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