Replies

1. 
   IdahoDon | Apr 09, 2008 12:49am | #1

   Essentially the same as pouring the same bare concrete suspended floor without the ICF.  The forms are well supported until the concrete cures.  Lots of rebar. Beefy bracing.

   Prestressed slabs can do the same thing.  You don't need bracing underneith, which is a big plus, but the detailing is more involved since a 4" over-slab is required.

   I like the idea of ICF's for insulating the space underneith and providing something to screw sheetrock to.

    

   Beer was created so carpenters wouldn't rule the world.

1. 
   Hudson Valley Carpenter | Apr 09, 2008 02:44am | #2

   Don,

   Let me lay out what I have in mind.  I'm going to be building a three story home on a sloping view lot with road frontage on the high end of the property.  The driveway will be at road level, retained on three sides by concrete walls. 

   The foundation of the house could be built separately from those retaining walls, down the slope a short distance.  The garage could then be built between the driveway and the house on a concrete "bridge" approximately 20X20. 

   The other option is to make the stepped footings continuous, tying the driveway's retaining walls to the main structure and adding another footing from side to side at the mid-point of the garage.  This would allow a separate concrete wall to be built as a support for the garage floor and as retaining wall to allow for two level spaces to be created below the garage, perpendicular to it's entry and the driveway.  Those two spaces would probably be about six feet different in elevation from one another.

   Which of the two ideas I use is largely dependent on the cost of those prestressed slabs you mentioned vs. the cost of pouring the floor in place, using ICFs or corrogated steel decking.  

   Following option #2, the span would be decreased to about ten feet.  Steel would be fine but what about those ICF forms? 

   So far I have no plans to build any living space under the garage.  Though that's a distinct possibility, at this point there's no plan to use that space for anything other than to store large things under cover.  That's why either option mentioned is open.

   I'm leaning toward #2 because it creates the possibility of storage for seasonal recreational vehicles and machinery but financial considerations are significant.  This is a spec house, two-three years for my family and then out. The extras storage space is difficult to access, being on a slope and so will not have universal appeal on the open market.  It would also add to property taxes.

   So that's where I'm at with it. What makes more sense to you?  Do you have any idea how those those two methods compare for cost?  How about the cost of the prestressed slabs?  I'm thinking big bucks there...delivered from who knows where and requiring a crane waiting on site.  Visions of hundred dollar bills with wings, like a migratory formation of honkers on their way elsewhere. ;-) 

    

1. 
   IdahoDon | Apr 10, 2008 03:52am | #3

   We had a smallish 15' x 18' area covered by precast slabs and it was $5k for the slabs, an engineer to turn a crank and stamp the plans, and delivery on top of the concrete walls.  Spendy, but I don't know what it costs to rent the supports for wood forms (or your ICF's on top of the ply forms). 

   Beer was created so carpenters wouldn't rule the world.

1. 
   Hudson Valley Carpenter | Apr 10, 2008 08:58am | #4

   Thanks Don,

   I was hoping that it would be in that price range, makes it affordable. 

1. 
   IdahoDon | Apr 12, 2008 04:51am | #5

   I think I mentioned it, but part of the cost of the pre-cast is an additional 4" slab that must be poured over the precast sections and includes a decent amount of rebar tying everything together.  This required a separate pour and forming that we could have eliminated going with something like the floor forms.  For longer spans I imagine the precast makes more sense, while smaller areas that are easier to support benefit from casting in place.

   Another issue with the precast is the ceiling isn't flat, but arches up in the middle and requires some additional work to hang drywall under it.  The engineers didn't want to allow ramset nails or concrete screws in the precast to support any ceiling firring, which seemed strange and made it a pain in the arse. 

   Beer was created so carpenters wouldn't rule the world.

2. 
   Hudson Valley Carpenter | Apr 12, 2008 05:34am | #6

   I understand what you're getting at about pre-cast concrete.  It looks a lot more useful than it is, after all costs and additional work is factored in. 

   I'm leaning more toward steel decking, although I'm not yet certain that it will suit my needs perfectly.  http://www.sdi.org/ 

3. 
   ronbudgell | Apr 12, 2008 02:18pm | #7

   HVC,

   Have you ever seen Hambro trusses in use? They are seldom used on single family residential constructiion, but they can be.

   Installation is within the capabilities of anyone who can form a good ICF wall, though you need a good floor finishing crew to pour the slab.

   http://www.hambro-floors.ws/www/v4/ehambro.nsf

   Ron

4. 
   Jim_Allen | Apr 12, 2008 03:49pm | #8

   Interesting system Ron. I've got it bookmarked. Bob's next test date: 12/10/07

5. 
   Hudson Valley Carpenter | Apr 12, 2008 08:25pm | #9

   Ron,

   Bar joists are certainly an alternate means of support, relatively inexpensive too.   

   I've been focusing on keeping the headroom open underneath but now that you've reminded me, a few bar joists and some corrogated steel decking may be the cheapest and easiest method.

   Thanks for reopening my old mind.  It makes a point about the difference between focusing and fixating.  ~!~

   Peter 

6. 
   BillHartmann | Apr 12, 2008 09:29pm | #10

   My house, built in 79, is a poured concrete slab over temporary plywood and bar joist supports. I have seen a number if this area done like that.But mine is part of the house. First floor on slab, 1/2 flight to basement under garage, 1/2 flight to 2nd floor, and 1/2 flight to garage.The basement is used for shop and office space.If I was doing it now I would definitly use or look at using ICF system (also for the large exposed walls on the sides). I want the insulation in the ceiling. But again, in my case, this is used space.BTW, there was a article in FHB about 2-3 years ago doing such a floor..
   .
   A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

7. 
   Hudson Valley Carpenter | Apr 12, 2008 09:50pm | #11

   Bill,

   Thanks for sharing your experience and the tip on the FHB article.  One of these days, when I've got a few extra bucks, I plan to buy the DVD'ed back issues.

   I've gone through a number of thoughts about whether to use that space for something other than cold storage and/or fair weather shop space. 

   For a number of reasons, mostly related to heating requirements, it just makes more sense to use it for recreational vehicles, machinery, building materials and even firewood. 

8. 
   cargin | Apr 13, 2008 04:19pm | #12

   Hudson

   One of these days, when I've got a few extra bucks, I plan to buy the DVD'ed back issues.

   Just pay $20 to get Internet access to FHB site. Then you can look up any article you want.

   I have found it to be very helpful.

   I can get articles or pictures to show people techniques that I use in the field. 

   I have a friend who built his 3 stall garage floor with ICF, with shop area below.

   This is a big garage, 3 generous stalls maybe 32' deep.

   The shop below has ICF on 2 walls and insulated for sound to the house on the other 2 wall.

   Temp stays between 60-65 year round. There are electric heaters in there but they are never on.

   Rich

9. 
   Hudson Valley Carpenter | Apr 13, 2008 07:09pm | #13

   Rich,

   Thanks for the head's up on the FHB internet access.  I'm guessing that's an annual fee.  If so, well worth it. 

   I'm curious about what was used to support your friend's ICF floor and how much of it.  I guess I can find that information from manufacturers and/or the FHB article on that topic.

   While it's tempting to make the space under the garage usable as a shop, there's such a large amount of surface which is exposed to outside air temperatures as well as ground temperatures, not to mention the other additional materials and labor, that it's impractical to do that on a spec house.  ICFs ain't cheap, no matter what the aim is in using them. 

   We'll probably be living in this house for two-three years, during which time I'll be able to use the basement's 20X24 "recreation room" as my shop space.  For recreation, we'll use one of the spare bedrooms.   

   I expect that the space under the garage will be fine for limited cold storage.  I was thinking this morning about taking a few good cherry logs from that property to the mill to be sawn for flooring.  That space would be ideal for drying anything like that. 

   Peter 

    

    

10. 
    BillHartmann | Apr 13, 2008 07:19pm | #14

    That is the price if you already have a mag subscription. I think it is $49 a year for online only.But you can also get it monthly, maybe $5.95, but not sure of the exact price.
    .
    .
    A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

11. 
    Hudson Valley Carpenter | Apr 13, 2008 07:25pm | #15

    Thanks Bill,

    The monthly deal would work well for me right now.  I'm on a tight budget until I sell this house. 

12. 
    cargin | Apr 14, 2008 01:57am | #16

    Hudson

    I'm curious about what was used to support your friend's ICF floor and how much of it. 

    I wasn't part of the construction, but I think they used a series of 2x6 walls that were later reused to build the house.

    Rich

     

13. 
    Hudson Valley Carpenter | Apr 14, 2008 03:26am | #17

    I think they used a series of 2x6 walls

    That makes sense. 

    Under the conditions which I've previously described, it'll be simpler to use corrogated steel decking, probably supported by a few bar joists.