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DaveBell
Moderator
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# Posted: 10 Apr 2016 07:24am
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http://www.small-cabin.com/forum/6_3459_0.html
What are the pros and cons of this foundation? Is it allowed by code? I would like to have a slab foundation for a 16x24 but it may cost $6000 with one whole load just for footers 24" deep.
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Don_P
Member
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# Posted: 10 Apr 2016 08:05am
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Pros, gravel drains freely, no water= no frost heave. If gravel gives you frost depth then you're good. Con... If the gravel can't just roll out from under it. That looks to be an issue here. The gravel can be in a draining trench under the perimeter to carry the thickened edge of the slab with just 4" of gravel under the body of the slab. Also look at frost protected shallow foundations in the code book.
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Steve_S
Member
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# Posted: 10 Apr 2016 08:32am
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The Monolithic Slab is what your after I believe. Note that there is a drop around the perimeter. Typically the slab is 4" thick while the perimeter is 8-10" thick by 8-12" wide. That would be for a typical Stick Framed structure... Log, Cordwood, Stone/Block require different perimeter relative to loads.
Takes the Slab one step further preventing thermal transfer between the ground & the slab itself which increases the comfort level. An additional bonus with FPSF foundations is the ability to plumb in PEX for Radiant Heat which when done properly can keep your heating & cooling costs down, increasing comfort and saving you the ever precious cash that's so hard to hang onto these days.
For Radiant Heating info & materials check out http://www.radiantcompany.com/ who I purchased my Radiant Kit from.
BTW: I supplied my own 4" XPS Foam for under the slab (bought from commercial roofer @ < 1/4 retail big-box $) but the Forming, Pouring & Setting with finish & sealer cost me 4K for a 20x24 pad + another 6x8 pad for my powerhouse (also pexed & insulated)
Concrete Options:
Check and see if there is a local Ready-Mix / Site-Mix concrete supplier. They come on-site and mix what is needed on site and pour... This is often cheaper than Factory mix and can be adjusted for your needs... Much easier to colour the concrete if going that route BTW.
Lessons Learned suggestion:
If possible have them use Fly-Ash in the concrete as it makes it stronger with tighter bond. You could also have them add Fibre Reinforcement into the concrete to prevent cracking (above & beyond the steel reinforcement).
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Littlecooner
Member
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# Posted: 10 Apr 2016 10:15am
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Agree with Steve_S on the adding of fiber reinforcement to any pad of this size under a building. It only cost a few dollars extra per cubic yard and will keep the slab from cracking over the years. You may also want to check the pricing of various strength of concrete. Most ready mix plants deliver 3000 psi if you just say " i need concrete". I would recommend looking at a 4000 psi concrete. If you go all the way to a 5000 psi concrete, that mix is almost indestructible even before you add the fiber.
I have no idea what part of the world you are in, but your estimated cost appears way to high for my area. A very close friend of mine just poured a 36 x 36 pad for his workshop about two weeks ago. The 4000 mix with fiber was about $ 110 or 115 a yard. the trucks are 8 yards and one truck would do your pad and some very large footers. That would be $ 1000 or so for concrete. Around here, I would be able to get professional finishers to finish that pad for $500-600. Add some gravel, build your own forms and you would have a pad for around $ 2000 in my part of the world with a little "sweat equity". I think i could even contract your pad here for half of what you though it would cost. Good luck on the build and if I was using that for a finished floor, would really look into that piping and heated floor, they are great in the winter months.
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bldginsp
Member
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# Posted: 10 Apr 2016 10:36am
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You asked about code- codes require any footing to be at least 12" deep in the ground, but you should go to the frost depth.
All the 'code compliant' slabs I see have a thickened perimeter footing at least 12" down, and minimum one #4 rebar top and bottom.
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