Two story house with concrete 2nd story floor?

[beppington]

When I was 14-15 I helped my parents physically build our house (2-story). Then, when I was 22-23 they helped me build mine (1-story).

So, I do have experience building a 2-story house, but with wood joists (2x12's).

I'm thinking about building my next house, a 2-story, with a concrete 2nd story floor.

The reason: The house is going in a somewhat low area "near", but not in, areas that can flood. My better half is very concerned about this, so our plan is to build a 2-story house where the ground floor is entirely garage/ utility/ work-shop, & the actual living area is all on the 2nd floor.

I've never liked the feel or sound-travel of wood-joists floors, so, if reasonable, I'd like to be able to make the 2nd floor "seem" like it's a standard, ground-floor concrete slab.

I always appreciate hotels that have concrete floors on the floors above ground floor. They just seem more substantial & quality, & you never hear noise penetrating thru them. I'm not sure how they make them, though. Is it all concrete? Are there steel beams? Are the beams inside the concrete? Is there not actually any concrete at all??

With the work-shop & garage being on the ground floor directly below the living area, & me being a night owl, I'd like to not have to be super-quiet while others are sleeping above.

So, the question: Will it be prohibitively difficult and/or expensive to make the 2nd story floor concrete, compared to wood joists? What might the cost difference be?

 

[/pine]

there is basically two ways...prestressed, precast panels are one way...the other way is using steel bar joists then corregated sheetmetal is laid over the joists and then a slab is poured on the metal...usually lightweight concrete is used...

the precast panels are hollow so plumbing and electric can be run through them

not sure of the cost differential between conventional wood floor systems but I would guess about double the cost of wood...just a guess

 

[rjkobbeman]

There are also floor trusses out there that are extremely stiff/strong.

I used engineered floor trusses made entirely out of 2x4s. They are 24" tall. On 16" centers with 3/4" Advantech subfloor, they are very stiff with no noticeable flex/give. I have some pretty long spans too.

Here is a link to some photos of my floor being put in: Rob & Kirsten's New Home - robert-kirsten-kids' Photos

The concrete idea sounds interesting, but there are other options out there.

If you do go the concrete route, I would LOVE to see pics of that going in. Sounds really neat!:thumbsup:

 

[beppington]

I used engineered floor trusses made entirely out of 2x4s. They are 24" tall. On 16" centers with 3/4" Advantech subfloor, they are very stiff with no noticeable flex/give. I have some pretty long spans too.

What's the sound transfer between floors like with those?

I know with my parents' 2x12 joist floors, 16" o.c., with 3/4" plywood floor surfacing (glued & nailed), R30 insulation, & 1/2" plastered drywall on the ceiling side (below), you can still hear somebody talking thru it, if they talk a little loud. And, if you're on the 2nd floor & jump up & land, a huge boom will reverberate thru the house. In the hotel floors I mentioned, you can jump up & land & it's basically just like a concrete slab on ground.

 

[/pine]

regular glass insulation (R30 insulation) does almost nothing for sound penetration...

they do make sound absorbing insulation for floors etc...

FWIW... the R value of dead air space in horizontal applications (where there is no convection) is quite high...

 

[rjkobbeman]

You can hear everything through my floors. Mine are not insulated, but you're right... that only helps a little.

I hear a lot more in my basement from the upstairs... because of the walking on the floors.

I can hear noise from my basement when I am upstairs, but not as much. I don't know if I will ever insulate my floor... so I can't help you there.

When my grandfather built his home, his basement included the space under his concrete garage floor. You never see that today. I think he did it old-school... a bunch of support underneath with a concrete-and-rebar pour. It was a two stall garage and I can't remember if he had a post in the middle or not for support underneath.

The precast products that /pine mentioned are pretty amazing today. I looked into some precast products to solve a bridge/creek problem I have. Never got beyond the "research" stage though!

 

[dpgood1]

Check your local zoning laws. Most areas require fire resistant material between garages and living areas. CO2 sensors are also a must have, even if local codes don't require them.

One thing that you could look into is sound deadening material. That stuff is usually not cheap.

Go by one of the commercial buildings being built and talk with the contractor to get some ideas.

 

[tallyho8]

My last house had a concrete floor over one bedroom that was the floor for a 2nd story porch.

Every winter we had a bad mildew problem on the bedroom ceiling as water condensed on the cold concrete above.

Your heated area will be above the concrete so your situation may be different.

The floor was very good soundproofing though.

 

[rjkobbeman]

Check your local zoning laws. Most areas require fire resistant material between garages and living areas. CO2 sensors are also a must have, even if local codes don't require them.

One thing that you could look into is sound deadening material. That stuff is usually not cheap.

Go by one of the commercial buildings being built and talk with the contractor to get some ideas.

I have living space above my garages. In my area, "firecode" drywall is all that was required. Had to have "firecode" man doors also.

 

[czechsonofagun]

That type of building is very very common in Europe. Even my dad's cabin has a concrete floor between the basement and first floor. Typicaly I beams (or S beams) and forms and rebar and pour it like a slab.

Or you can use steel beams and build the floor from prefab beams - either concrete or brick clay - it helps with sound proofing and insulation since the brick clay beams are hollow.

All that said - good luck finding it in good ole USA. If it's not a pine dimensional lumber it is very hard to find. One of the ICF makers makes styrofoam beams you put in place and pour slab on top of it. Here, check it out.

 

[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