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Author Topic: Partial basement under slab on grade? Getting mixed reviews  (Read 2508 times)

wreckit87

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Partial basement under slab on grade? Getting mixed reviews
« on: November 17, 2017, 11:44:56 AM »

Hey fellas, I'm hoping someone can shed some light on this for me. Next spring, I'm looking to build a new shop/shouse on some undeveloped acreage. Thinking 60x80 or 60x100 slab on grade with 2x6 walls, 20x40 sectioned off for temporary living quarters. The deal is, I plan to build an ICF house in a few years when finances allow, also slab on grade, on the same parcel and would like to have a small partial basement under both for the mechanical rooms. I know it's a sin here but this will be Geothermal in both buildings with a solar array on the shop roof, both of which have far too many credits to overlook and will put me money ahead in 8 years. When the house goes up, I intend to build an ICF tunnel connecting the two because I hate winter and like secret rooms. I've talked to 3 different local concrete companies and they all think I'm nuts (I probably am) and that it's impossible, but I don't see any reason why one couldn't do what I want as long as there's a frost footing around the perimeter under the slab so it's monolithic. Shouldn't be any different than an attached garage when the house has a basement, right? They move together in bad frost upheaval with a proper frost wall, why couldn't a monolithic slab? I've spent days on Google trying to find some information and have had zero luck. Anyone ever done such a thing?
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Cabo

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Re: Partial basement under slab on grade? Getting mixed reviews
« Reply #1 on: November 17, 2017, 03:12:56 PM »

My shop/garage is done with ICF's with a slab poured over for the upper level.  I used corrugated bridge panning and poured a 5" slab on top.  I've also done a car museum for a client with regular poured walls, bar joist and bridge pans.  That was 42' X 60' freespan (no posts in basement, completely open).  All kinds of possibilities but if nothing else, get an engineer involved.  Spending a few dollars up fronts will save you many thousands down the road if something goes wrong.
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mlappin

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Re: Partial basement under slab on grade? Getting mixed reviews
« Reply #2 on: November 17, 2017, 03:38:55 PM »

I really don’t see why not, all our grain bins are monolithic pours, largest is 36’ diameter with lets say a 37’ foundation.
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wreckit87

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Re: Partial basement under slab on grade? Getting mixed reviews
« Reply #3 on: November 18, 2017, 08:03:27 AM »

My shop/garage is done with ICF's with a slab poured over for the upper level.  I used corrugated bridge panning and poured a 5" slab on top.  I've also done a car museum for a client with regular poured walls, bar joist and bridge pans.  That was 42' X 60' freespan (no posts in basement, completely open).  All kinds of possibilities but if nothing else, get an engineer involved.  Spending a few dollars up fronts will save you many thousands down the road if something goes wrong.

I'm only talking like a 20x20 span, just to bury the mechanicals in the basement and have tunnel access. I work commercial construction and have seen a lot of bar joist/ bridge pan construction, and that is my plan for the second floor of the house as well as the deck in each of these basements. 42x60 is really an impressive freespan!! Wow. I'm only wondering if since it's going to be a partial, that the frost upheaval will be different between the floating slab portion and the basement portion, causing stress issues. Like I said, the local guys I've asked about it have said it's completely impossible and treated me like the moron that asks stupid questions. A footing/ frost wall around the remaining perimeter of floating slab should, in theory, keep it monolithic. Right?
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Cabo

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Re: Partial basement under slab on grade? Getting mixed reviews
« Reply #4 on: November 18, 2017, 08:34:09 AM »

I would think as long as your on good soils and below frost line with your footing you would be fine.  An engineer will have some recommendations for pouring the slab from the full basement to the frost wall/slab area such as rebar/expansion joint, ect.  Your ideas are completely doable but the contractors you've spoken with are probably just not familiar with that type of construction.
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Cabo

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Re: Partial basement under slab on grade? Getting mixed reviews
« Reply #5 on: November 18, 2017, 03:09:50 PM »

Just realized that I never commented on your interest in an ICF home.  I've done 6 ICF basements (3 for myself) and have nothing but good things to say.  I've wanted to do a entire house out of them but ambition level is dropping as I get older but I would encourage anyone to do so.  The things are well insulated and virtually bulletproof.  Construction techniques vary a bit and that's why I think people are hesitant but if you're will to research the process I think you'll find it fairly easy.  Start out level and straight, then its just like putting Lego's together.  Good luck.
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wreckit87

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Re: Partial basement under slab on grade? Getting mixed reviews
« Reply #6 on: November 18, 2017, 09:16:12 PM »

Just realized that I never commented on your interest in an ICF home.  I've done 6 ICF basements (3 for myself) and have nothing but good things to say.  I've wanted to do a entire house out of them but ambition level is dropping as I get older but I would encourage anyone to do so.  The things are well insulated and virtually bulletproof.  Construction techniques vary a bit and that's why I think people are hesitant but if you're will to research the process I think you'll find it fairly easy.  Start out level and straight, then its just like putting Lego's together.  Good luck.

Thanks! Any recommendations on tying the second floor slab into the sidewall? I've seen some use the L blocks on the top course and lay insuldeck or something across after the wall is poured, then pour the slab, then start stacking blocks on top again, and others that build the wall all the way to the roof first and anchor beams into the wall after it's cured and support the slab off of them. Never seen it done in person nor talked to anyone who's done it.
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Cabo

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Re: Partial basement under slab on grade? Getting mixed reviews
« Reply #7 on: November 19, 2017, 04:49:11 AM »

Typically around here you would install install an engineered wood floor system inside your ICF's similar to a balloon framed wooden wall structure.  I'm sure in a commercial application it would be done how you described.
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