Lowered ceiling for half a room

[Mainer]

As you can see in the attached, my main floor garage floor is about 6" lower than the adjacent rooms. The floor system that supports this garage is very thin, which is unrealistic. I think the software is giving it a 4" slab instead of 12" floor joists. In reality I'll probably have at least 12" trusses supporting the 4" slab to carry the two vehicles. The full width room below is my basement garage-workshop. I'd like to depict that half of this room will have a lower ceiling due to the support the garage above will need. I believe my only two options are either an invisible wall and setting the ceiling heights differently, or placing a full width and depth 12" soffit at the basement ceiling to represent the ceiling trusses.

I'm leaning to the soffit idea but wanted to get other opinions. What would you do?
Thanks.

[daydreamer]

Hi Phil,

I think I would look the attached information over and discuss this aspect of the plan with a structural engineer. (see attached)

I think 2 x 12 are risky.

Here's a link for you to take a look at.

I wouldn't like to see those vehicles and the concrete slab in your workshop. That would be a lot more mess than the stairs on stairs.

http://www.huduser.org/Publications/pdf/res2000_2.pdf

[Allen42ACJ]

Phil
There was a good thread at CT about this with links to where you can get the floor system..
If I find it,will let you know..

[Mainer]

Thanks to both of you. The floor support will be designed by the truss company engineers. I'm just looking to make some kind of fair representation in my plan of what the truss system may be and didn't know if there was an advantage of using a soffit verses dividing the room in two and having a lowered ceiling.

[daydreamer]

Hey Phil,

If it's for looks, I think I would go with the Soffit. It seems it would be pretty easy.

[Allen42ACJ]

Open the room DBX and change it in the structure tab..
Check it in the basement after to..

[Mainer]

I took Allen's suggestion, which is I opened the upstairs garage room, selected the structure tab and changed the floor to 20" thick (hopefully, that should do it). and the result is in the attached pics. I had to offset the lights 20" below the ceiling cause they were not visible otherwise. The side view really doesn't show the 20" thick floor very well.
Thanks to all.

[Allen42ACJ]

Phil
What do you have for the floor joist?
You may have to build the floor framing and have it on in 3D.
You could just fill it in with a cad box with a fill style..

[Mainer]

I won't know what the floor joists will be until my carpenter brings the plan to the truss company and they design them. Currently, I've just specified a 20" concrete slab for the upstairs garage to get a visual effect. That 20" will probably be 4" of concrete and a 16" truss beneath it. I'm not familiar with how to have the software make a floor like that?

The plans I'm making are primarily for room size and placement, roof style, window placement, etc. They are not intended to dictate the structural design or integrity. That will be determined by the carpenter with the floor/roof truss company. Our City uses the BOCA building code and as long as the roof and floor truss plan have an engineer's stamp on them (provided by the truss company), I don't need to do that work (not qualified to anyway). My goal is to visually provide some space that hopefully accomodates what the engineer wants to put there. If I don't leave enough space visually, then we adapt as we go along.

[Larry]

I won't know what the floor joists will be until my carpenter brings the plan to the truss company and they design them. Currently, I've just specified a 20" concrete slab for the upstairs garage to get a visual effect. That 20" will probably be 4" of concrete and a 16" truss beneath it. I'm not familiar with how to have the software make a floor like that?
.

I have a friend that did this to an existing house and here is what I remember from it.

Aside from pouring more inside walls to actually hold the floor up.
He installed, what he called "pre-stressed concrete". This consisted of rebar about every 6" apart spanning the width (22'+) on little stands to place the rebar up about one third of the concrete thickness. He was instructed to pour 5 or 6" (can't remember now) of concrete on this. Being nervous he poured 7" of concrete on it. After about a month he removed his supports and has been doing wordworking under his truck and car for the last 6-7 years now. No cracks or problems.

This was designed by an Engineer and plans stamped.

In short: It doesn't take that much thickness if steel rebar takes up the pull slack at the right position.

I could contact him for more detail if needed but it will be up to an Eng. If you get killed under there you need to know who to sue....LOL

[daydreamer]

Phil,
What do you do for a floor drain? If you don't have a drain, what do you do with the water that will get in, especially from melting snow on the vehicles? You don't have any concerns about drainage?

Is this a common design in your area?
I've never seen a design done like this.

With all the land you appear to have in the picture in post #13 of the following thread http://hometalk.homedesignersoftware...ead.php?t=5755 you couldn't find a better solution for a garage?

I agree with you Larry. This looks like a nightmare waiting to happen.
Larry said, "If you get killed under there you need to know who to sue....LOL" and I say, so your family knows who to sue.

[Allen42ACJ]

http://www.chieftalk.com/showthread....t=garage+floor
Check out this thread..

[daydreamer]

I don't doubt that it's been done. God knows we drive across bridges with pre-stressed concrete supports and decking all the time.

But, to me... it seems a bit of a stretch for a residential home. Maybe Phil just want to have something really unique.

[Mainer]

Rick,
Since the ground will freeze as much as 6' deep under a snowplowed driveway in my area, garages typically have a full foundation under them if they are attached to your home. I know that putting a basement under such adds the cost of digging out the dirt and pouring another slab, but it is not that uncommon in my area (my family owns several skid-steers for digging). My current two car garage (20x24) has a full basement under it connected to the house basement. My father's house has the same. Whether or not a few steel support posts and maybe a metal I beam on the other end will be needed is the question the engineers will answer.

As for floor drains, we put one under the center of each vehicle's axles to drain away the melted snow. The drains are piped through the floor to the basement below into a large trap below which is emptied out once to twice a year of any sand that got in it. It is then drained outdoors to daylight.

My father has built a few 20 to 40 apartment buildings and he always has a concrete slab as the floor of the second story level. That is standard practice in our area.

[daydreamer]

Phil,

Thanks for filling me in. Like I said in my reply I didn't doubt that it had not been done, I just didn't know how much it was done. Each area of the country has its conditions. You are lucky to have a basement. We don't have them here in Florida.