Two story house with concrete 2nd story floor?

[AMR]

I manage the construction of buildings for colleges and universities. All of the buildings we construct are concrete foundations, frequently on piles and the like, steel frame, typically masonry exteriors with concrete masonry unit back up, complex air/vapor barrier systems, slab on deck, etc. slate roofs, on and on

I finished my house 5 years ago, conventionally framed, glue-lams, LVI's, TJI's, etc. and I kick myself for not considering things like slab on deck, etc.

I am a civil engineer and I have been dealing with construction for 18 years now, it is startling how completely foriegn the residential construction industry remains to me. Working with the GC that I hired to build my house I just couldn't believe how loose the residential construction industry is and how much quality varies from person to person.

I tried to run my house construction like a commercial project but it was useless.

I know I will build another house in the future and I am definately going to mix in more commerical and institutional elements. A 4" concrete slab on deck between the basement and level 1 and then level 1 to level 2 would be infinately better then conventional wood framing for transmission of sound, mass does a lot to help with transmission of sound.

One of our neighbours has a concrete house with conventional hardi-plank and azec over it. It looks beaeutiful but I think that they are into a 2,900 SF house for nearly $1 M. It is extremely energy efficient but I am not sure they will ever see the payback nor sell it for its cost.

 

[beppington]

Wow, this is some great discussion! Thanks to all ...

I'll definitely post pics whenever I get going, assuming I can afford any of the alternates being discussed.

My dad just told me he knew a guy that built his house on the Gulf Coast; It had to be built up due to shore proximity, & he had concrete piers & a concrete floor ... & he said the piers + floor were about 1/2 the cost of the whole house. I don't need piers, but ...

 

[Duffster]

Wow, this is some great discussion! Thanks to all ...

I'll definitely post pics whenever I get going, assuming I can afford any of the alternates being discussed.

My dad just told me he knew a guy that built his house on the Gulf Coast; It had to be built up due to shore proximity, & he had concrete piers & a concrete floor ... & he said the piers + floor were about 1/2 the cost of the whole house. I don't need piers, but ...

Maybe not piers but piles. One of the biggest problems with the amount of concrete you are talking about is pouring enough footing to get enough surface bearing area. That may be tough to do if you are "near" flood areas.

I think prestressed will be the lightest and best option.

 

[beppington]

Maybe not piers but piles. One of the biggest problems with the amount of concrete you are talking about is pouring enough footing to get enough surface bearing area. That may be tough to do if you are "near" fold areas.

I think prestressed will be the lightest and best option.

The ground floor garage/ utility/ work-shop area would be fully enclosed, having a concrete foundation, and the exterior ground floor walls would be either block or poured concrete.

My intent is for the house to look like a common 2-story house from the outside, when in reality the 1st floor (ground floor) is entirely garage.

 

[MarkV]

As has been said it sure is doable. Where you will run into problems is crossing over into the commercial constitution trades to find contractors that are familiar with that type of build. It is a different world from residential construction. I'll bet you will raise the cost of your build by a 1/3 minimum.

It sounds like noise transmission is your biggest issue. I think you will find less expensive ways to do that than pouring a free span, open garage/workshop below, concrete second floor. If noise in your garage coming from above is that big of issue to you I would look into some of the spray foam applications available. Most are for insulation value but some are designed for sound proofing.

MarkV

 

[buckeyefarmer]

I've seen a deck on a new house near me that has a concrete deck built off the 1st floor, with a walkout under it from the basement. From the road it looks like prestressed sections of concrete that are put together like a parking deck is done.

 

[Larry Caldwell]

Concrete second floors require some engineering. The primary consideration is the behavior in earthquakes of hanging all that mass in the air. The basement walls have to be some pretty strong shear panels. The floor itself is pretty simple. Either you can do as others suggested and lay precast, or you can form up a pan, tie in a bunch of rebar, and cast the second floor in place. A good engineer will draw plans and cut sheets that would let any contractor do a good job, reinforced by the engineer inspecting the rebar before the pour, spec'ing the concrete batch, and having a testing lab break core samples to make sure the concrete came up to strength. Even if you do precast, you are going to have to have an engineer do the foundation and basement walls.

A few years back I did an underground house with a concrete roof covered with 6' of soil. The engineering and plans were pretty straightforward. A concrete slab can be as strong as you want it to be.

 

[MikeD74T]

beppington, all the engineering you need for cast in place concrete, 2nd floor or 39th floor, can be found in 'Architectual Graphic Standards".
Amazon.com: Architectural Graphic Standards, Tenth Edition (Book only) (9780471348160): Charles George Ramsey, John Ray Hoke Jr.: Books
Gives concrete thickness, rebar size & spacing, etc based on clear span. Also cast beam specs. That's where the engineers go. Your idea is very DIY if you're willing to research the tradesmen/contractors in your area. One caution, be very thorough in your planning for electric, hvac, etc. After thought holes in cast concrete are tough to accomplish.

I did a 16'x18' clear span cast floor a few years ago for a friend. He'd seen my house with cast floors & trusted my judgement (which I gleaned from AGS). Building inspector wanted an engineer's approval before he'd issue an occupancy permit. We went a little heavier on the rebar to pour before the engineers results came back. The 6" slab spec came back at 125 psf where only 40 psf was required. You'd have to hit that slab with a hammer to be heard on the other side. For forms I set up staging, put 2x10 planks on edge & corregated steel decking on the planks, & covered with 6 mil poly. 28 days later removed the staging, planks, & metal. MikeD74T

 

[Kays Supply]

I have worked on apartment buildings that have had the 2x4 floor truss system and 2" of ultralight concrete poured on top of a plywood floor. You can't screem loud enough to be heard between floors. We had to get walkytalkys to talk to each other. The put the wall plates down before they poured the concrete so the electrical and plumbing could be drilled. We had them put slabs of 2x12 where the tubs and stools were. After the second building we had the kinks worked out pretty good. It is pretty easy to put a sprinkler head or two in the garage area using city water just in case. If you are going to put any tile you need to put a plastic matt down before because the concrete tends to crack near doors. It worked so well the contractor started using it on all concrete floors. The truss floor system is a dream for the mechanicals, HVAC and plumbers love them.

 

[winstonfiore]

Hi Beppington,

I see it's been a few years since this thread was active. Did you ever end up going forward with this idea? I ask because I recently had this exact same idea myself. My girlfriend and I will be putting down roots in New Orleans, and flooding is a concern in the area as well (understatement). I thought a workable solution could be to build a home whose first floor is a garage/workshop and whose second floor is the living area on concrete. Upon googling around, I came across this forum...

I'd be curious to get a follow-up from you. Assuming you went through with this plan, how much did it cost you? How did you structure it? Any chance you'd be willing to share blueprints? I'll take any advice you can muster! Thanks so much,

--
Winston Fiore
Sgt/USMC
smiletrek.org