# Concrete Slab vs Block vs Pier / Post Foundations



## carpenj4 (May 30, 2013)

I am working on an estimate and was wondering if, given my project, a concrete slab, block, or a concrete pier / wood post foundation would be best for a 15 x 30, two-story room addition? The home is on a slab foundation. The addition will be going on the top crest of a hill. Any suggestions, or additional information you would need to make a suggestion just let me know. Thanks.


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## FramingPro (Jan 31, 2010)

carpenj4 said:


> I am working on an estimate and was wondering if, given my project, a concrete slab, block, or a concrete pier / wood post foundation would be best for a 15 x 30, two-story room addition? The home is on a slab foundation. The addition will be going on the top crest of a hill. Any suggestions, or additional information you would need to make a suggestion just let me know. Thanks.


The problem i see with putting a slab there is that the ground at the top of the hill will be in an area where erosion can occur. Erosion, even if it happens over time will be detrimental to any slab. That being said, in my professional :laughing: opinion i would opt for a sonotube pier foundation capped with a wood subfloor.


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## concretemasonry (Dec 1, 2006)

For minimum initial site impact and for long life as erosion inevitably goes on, I would look at Sonotubes in augured holes with posts above the minimal projection above grade. - Not as much soil to get rid of and the tubes could be filled one at a time with no major material problems. Footings and piers require more material moving to get to a proper depth.

Going deeper is a plus because the top of a slope always will erode over the seasons and years. This always allows drainage with minimal changes.


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## AutumnWood Inc. (Aug 17, 2007)

carpenj4 said:


> I am working on an estimate and was wondering if, given my project, a concrete slab, block, or a concrete pier / wood post foundation would be best for a 15 x 30, two-story room addition? The home is on a slab foundation. The addition will be going on the top crest of a hill. Any suggestions, or additional information you would need to make a suggestion just let me know. Thanks.


Wouldn't code dictate the foundation to be used ?

I know here in the Detroit area ... If your doing a 3 seasons porch you can do post and beam deck style sub floor. 

But if your doing 4 season living space you have to have a trench footing around the perimeter of the addition. 

So here it would be a 12" x 42" footing for a 4 seasons room - slab floor or block and wood sub floor.

With the grade issue ... Footings - block for the grade transition, and wood sub-floor would seem best if again it is going to be a 4 season living space addition.


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## SticksandStones (May 13, 2013)

How many piers and what spacing are you using? I am pondering a 20 x 24 ft workshop/shed in my own yard for tool storage, and am facing similar problems. any help is greatly appreciated.


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