Raised floor on concrete slab

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  #1  
Old 07-07-09, 08:53 PM
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Raised floor on concrete slab

Hello,
I'm planning a renovation of a former garage off a kitchen. The kitchen doorway opens to the garage where there is currently about a 16" drop (two steps) to the concrete garage floor. I would like to extend the kitchen floor out the door about another 8-10 feet into the garage to allow room to add a pantry and a small half bath. This would allow the pantry to feel more like part of the kitchen and make the half-bath easily accessible (also the raised floor makes the plumbing for the bath easier).

So my question is how to best build the sub-floor structure on the concrete slab...and make sure it is even with the existing kitchen floor. I assume on the kitchen wall side, I could attach joist hangers to the rim joist to get level with the current floor. On the other end of the new floor joists, how is the best way to anchor on the concrete floor support for the joists 16" up?

Thanks,
Guy
 
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Old 07-15-09, 12:19 PM
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- Knock knock.
- Who's there?
- Bump.
- Bump who?
- Bump, to see if anyone has any ideas for me...
 
  #3  
Old 07-15-09, 01:39 PM
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Is the garage floor level? often they slope to the outside. So you need to take that into consideration. I wood position a double 2X8 ten feet out from the kitchen.. The exact height would depend on the flour you planed to install. Example if you planed to use two layers of " CDX plywood and sheet vinyl it would be approximately 1" lower then the kitchen floor.

Frame in the garage door with a 2X4 stud wall. Run a rim joist of 2X8 across the front and rear of the garage and with joist hangers temporarily support this beam at the right height. Align the double beam to a set of doubled studs behind the rim joist in each wall.

Build a concrete form box approximately 15" by !5" just high enough to slide under the 2X8 double beam in the middle Fill with concrete up to the beam and let set.

Using joist hangers between a rim joist on the kitchen wall and the double beam install 2X8s on 16" centers. Note this assumes southern pine 2X8s and a span of less then 13 feet and a span of no more then 16 feet for the double 2X8 beam.

The 15"X15" for a poured center support is a gut measure not based on engineering specs. You could also just block up under the beam using a 8X16 four inch thick concrete pad and then various thickness of board and plywood. You may want to use two supports between the rim joists.

Ok really all is gut engineering so wait for corrections from the experts. If I have misunderstood and you plan to use the whole garage then the double beam won't be needed.
 
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Old 07-15-09, 05:27 PM
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To further Ray's comments, depending on the width of the garage, place those concrete piers about 8' apart, or divide the garage into thirds and put two of them, at least. You will be using the existing framing on the side walls and on the door wall to support your rims, so that support is probably all you will need.
Just make sure your ledger is level and at the proper height to take into consideration the subflooring, or any other flooring you plan on using (hardwoods, tile, linoleum, carpet).
NOW, you have just closed one method of egress from your house. You need two. Is there a door that exits to the ground nearby? Not to a deck, but to the ground. Do you plan on installing a door at the back of the pantry to access the garage?
 
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Old 07-17-09, 09:11 PM
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Thanks guy! (I apologize for the bump...I'm not that clever) I will try to post a pic that might help to clarify what I'm going after.

Basically, current garage is 21' x 25', with the kitchen door more or less centered on one of the walls. From that kitchen, I'm trying to extend a 8' x 8' area at the same floor height as the kitchen (approx 16" above the current concrete floor). So this raised square area would only share one wall with the kitchen, the rest would be in the middle of the garage.

I understand the joist and beam design described above, but isn't there some advantage to distributing that load across the garage floor instead of concentrating that half onto two piers?

Again, if I can figure out how to get a pic of my design that I have in mind, I will post it.
Thanks again,
Guy
 
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Old 07-17-09, 09:42 PM
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I understand the joist and beam design described above, but isn't there some advantage to distributing that load across the garage floor instead of concentrating that half onto two piers?
The ledger beam (double 2X8) also transfers load to the rim joists on either end, That is part of the reason I suggested a double stud behind the joist hanger on the rim joist where the ledger beam is. That double 2X4 acts as a post. You could run a 4X6 underneath the floor joists at their center point if you want to over engineer a bit

Of course you could just build a stud wall from floor to ceiling instead of the double .2X8. Then just fasten a single 2X8 to that wall as a ledger for your joists. No piers needed. Actually better then my original idea.
 
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Old 07-17-09, 10:41 PM
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If you are in the planning stages for a permit, great. I did a garage conversion the County had me build an engineered short wall with osb sheathing and concrete footings under it with seisic hold-downs. You need to transfer the floor load to the footings, not the slab. Check with your local B.D. for safety codes.

Egress through a garage is not a problem, it doesn't pertain. On the main level, only one side hinged door 36" wide is required, and an egress window in every bedroom. Be safe, G
 
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Old 07-18-09, 01:57 PM
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OK, here are a few images of what I have in mind. Note, the stuff with color is the existing kitchen wall, while everything in white is what I'm planning to add:









A few questions:
1) Does this look overall feasible?
2) Can I just use joist hangers for all the joist hanging from the new rim joist (which is attached directly to the studs on the new walls)?
3) Any special watchouts around the new step area?
Also note, I will be adding a wall on this raised area basically dividing it into a hall and a bathroom.

Thanks for the help!
Guy
 
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Old 07-18-09, 06:56 PM
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G, egress does matter if that main level has no egress sized windows, so lighten up a little on stopping safety concerns from entering the posts. Some shotgun type kitchens I have been in are almost tubular in design with a door at the end and no means of egress within 20'. The kitchen window, if any, wouldn't suffice, in those instances. So egress from a door to safety would make sense. Now the OP may have a different design, and we'll let him and his inspectors decide on his particular situation.
And the OP is working under the Southern Building Code, which may differ from where you are located.
 
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Old 07-18-09, 08:17 PM
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Chandler, I wasn't stopping a safety concern from entering the posts. I understood the codes to only require 1 door to the exterior, without a second door or window on the main level for egress, other than bedrooms.

1. Egress for a house is through a 36" hinged door, as I stated.
One door is all that is required for egress on the main floor and not through a garage. The garage/house walls need fire stopping wallboard, metal duct penetrations, weather stripped self closing door, etc. But it is not an egress path.

2. I'm having difficulty finding the code on a second means of egress (other than bedrooms) required on the main level. Do you have the number and type for me? It may be a local thing.

3. Egress not to a deck? The deck must be securely attached to the building is all I've found. There must be thousands of front decks with a front egress door, just around here. This must be a new code I'm not familiar with, where is that number, please?

4. A window for the main level is required for egress. I can only find window size for light and ventilation, other than bedrooms. I could be wrong, could you tell me the code number on that, as well, please?

"floor load to the footings, not the slab. Check with your local B.D. for safety codes." I usually include that, as I did this time. I'm all for safety, and always open to new rules and regulations. These new rules you stated may be in the new codes, and I only have the new revisions of them. Im truly interested in their numbers and which book, thank you.

Door with direct access to exterior req'd (not through garage)
. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . ... . .[311.1] {1005.3.2.3}

Bedrooms & [habitable] {all} basements req. emergency escape to exterior
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [310.1] {310.4}

Be safe, G
 
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Old 07-18-09, 08:28 PM
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I am south of Nashville so my suggestions may not apply. Piers are not used here. Blocks of block and beam usually rest on 16"X16"X4" thick pads just enough into the ground to level. Concrete floors generally don't have peers. I saw the slab as a thicker stronger substitute for pads. My answer may well have been totally wrong for his area so please ignore.
 
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Old 07-19-09, 05:26 AM
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G, Egress to a deck without stairs, probably would have been a better choice of words. Such egress wouldn't help, as in our local area, where most decks are 12' off the ground.
And the reference I mentioned may have been purely local, but our inspector insisted we not block off any exits that were already built into the house, or provide for additional egress if we did, in addition to the front door. Quite often the front doors of these houses is not 36", but 32", so it could have played a part.
 
 

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