Replies

1. 
   jhausch | Nov 18, 2002 06:05am | #1

   http://www.spancrete.com/

   have at it!

   Steelkilt Lives!
2. 
   gordsco | Nov 18, 2002 06:28am | #2

   Any way you slice it, you'll need an engineer to sign off on this one. Hope your car stays out of the family room.

   Gordsco

1. 
   BillHartmann | Nov 18, 2002 06:47pm | #4

   "Any way you slice it, you'll need an engineer to sign off on this one. Hope your car stays out of the family room.."

   I don't understand what you are talking about. My home was build over tw..

   Wait!

   What is that sound?

   Is it the car falling through floor!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

   Ops, sorry false alarm. It was just the dog knocking something off the coffee table.

   As I was saying I build the house in 79 and the car has not fallen through the floor on to my table saw yet.

   This is one of those things that everyone automatically thinks is "impossible" until they look into it.

   First of all look at the loads. While the loads are concentrated at the tires the over all load is not that great, about 50 to 75 lb/sq ft. Just a little more than residendtial framing.

   Apparently it there are some variation in local practices. Where I am concrete floor poured over temporary supports is common.

   Mine is 24 x 24 with a steel I beam and center post under it. Plywood was used for the form than then steel joist where put under it to support the weight. I believe that it is just a 6" slab with a moderate amount of rebar in it. And no engineering drawings, but the part of the designers house plans.

   However, if I was building today I would look at some if the insulated foam form systems. One of the problems with mine is insulating the ceiling.

1. 
   gordsco | Nov 19, 2002 02:33pm | #8

   I didn't want the poster to think it was impossible. I wanted the poster to note that depending on the length of span etc. there would be some considerations best dealt with by an engineer. If you were to buy precast engineered slabs, they would be designed and rated to carry a specific load over a certain distance. Site poured overhead slabs are loaded with variables, and are not a common addition in residential construction.

   The last one I worked under was a 3 car garage over a 20'X20' home theater, site poured, full span, no posts. A combination of concrete and steel beams. They eliminated the insulation and opted for in slab heating. The biggest concern for the inspector was the basement entry from the garage. The exhaust from an idling car travels downward, so special attention was given to carbon monoxide sensors and two sets of self closing insulated doors so that everyone who died in the home theater was in a movie.

   Gordsco 

3. 
   MADCARPENTER | Nov 18, 2002 07:08am | #3

   me too

   i'm planing almost the same thing hopefully this spring. i,m building on a hill faceing a lake & want a work shop faceing the lake on the lower level with lots of windows as it faces south but property size & layout determins that if i want a garage it must be within the same foot print. it is also inportant that i keep the overall hieght of the lower level to no more than 8 or 9' to keep the elevations looking apropiate to the house but of course being a shop i need as much head space as possible....therefore i was thinking the same "I" beans with a reinforced cncrete pad..I guess a engeer will be nessecary however the more research we do up front the more time + dollars we should save on engeneering costs. I will keep you informed of any progress I make & wish you luck(meaning good planing)

   mad

1. 
   JohnFinn | Nov 18, 2002 09:27pm | #5

   I did one about a year ago, and after going back and forth between "conventional" reinforced concrete poured in place (on plywood forms, steel I-beams) we decided on a hollow core precast floor system. The final engineering was done by the precast company, along with accompaning drawings to submit to the building dept. The "slab" panels were 8" thick, and we also had to consider a 4" "leveling" top coat, which enables you to pitch the slab to drain, and also takes care of panel edge gaps. The slope of the lot allowed us to put in a pair of 3068 steel doors in the rear wall, which worked out good. Since finish floor of the garage was 1'-8" below the main level, we ended up with a 7'-8" height below the garage, which isn't too bad. The house had a 9' poured wall with a course of 8" block.

1. 
   MIKEDELTA2 | Nov 19, 2002 01:42am | #6

   What you need is a Puerto Rican builder, when I was stationed in Puerto Rico you see this all the time because a lot of houses are built on the side of the mountains, and the houses are usually made out of poured concrete or blocks with a sort of concrete stucco put on.  My friend lived in one where the garage was on top of two floors, middle one the public areas with the bedrooms on the bottom, when him and his wife were going through a divorce he use to joke about borrowing a full cement truck and parking it in the garage when his wife was sleeping.  Come to think of it the beams holding the ceiling must have been hidden pretty good because the rooms had smooth ceilings.

1. 
   Boxduh | Nov 19, 2002 02:13am | #7

   My garage is that size, and has a heated shop under it.  One of my options was to use the steel fabricator, with a P.E. on staff who would engineer the deck, and sign and seal the drawing.  We had a couple options, both involving one WF steel beam to carry the deck load at midspan.  One option used a small section WF and a center column, the other option had a heavier WF section and no post.  Both were to use 24 gage corrugated deckform sheet , with a WWF-reinforced 4" slab top.  Since my shop is heated, I chose to use a forming product called LiteDeck, which is a styrofoam form, in 24" width sections, each tongue and groove edge forms a beam pocket, so your deck is a series of concrete T-shaped beams, with resteel in the bottom of each beam.  Either approach, using steel and deckform, LiteDeck or something like it, or plywood forms, will require shoring at the 1/3 span points before the pour.  LiteDeck referred me to an engineer who came up with the resteel configuration and provided signed and sealed drawings.  With 2 to 8 inches of foam against the bottom of my garage floor structure, I get good insulation.  Be sure to use a commercial deck coating for the garage floor surface, as cars drip, and concrete cracks, and you don't want any water seeping through, ever, not a little tiny bit.  We used a Sonneborn product that is a moisture-curing urethane, with a 40 wet mil primer, and a 40 wet mil topcoat, sprinkled with granulated rubber and backrolled in, for traction.  It is not like getting free square footage; forms and shoring and the extra steel all cost money, and insulation will, also.  Figure that you will save, though, more than the cost of erecting a separate garage-sized building somewhere else on you property.

1. 
   BillHartmann | Nov 19, 2002 05:30pm | #9

   " It is not like getting free square footage; forms and shoring and the extra steel all cost money, and insulation will, also. Figure that you will save, though, more than the cost of erecting a separate garage-sized building somewhere else on you property."

   Don't forget the cost of doing it the other way. Of course it all depends on the circumstances. But a lot of time you have to bring in lots of fill and compact it and add some piers and/or grade beams.

   " Be sure to use a commercial deck coating for the garage floor surface, as cars drip, and concrete cracks, and you don't want any water seeping through, ever, not a little tiny bit."

   I had some old oil from my boat setting way back in the corner next to the overhead door. I don't have that much so it is usually everyother year I take it to be recycled. One of the containers broken and leaked for a while before I saw it. The oil ran down the edge of the slab and under the cold joint between the slab and the foundation wall.