Replies

1. 
   toolpouchguy | Jan 25, 2011 05:29am | #1

   IMO would do the walls footings a lot easier to frame and water proof, built a garage a few years back and did the slab on grade works well ,but it was hard to waterproof ,but worked out ok the owner is very happy .

   same idea spray floor with hose and walls .used puck board 4' up installed hoist large loft above 

   my own  work shop is a slab mono pour it is hard to clean floors 

   with the poured walls and slab it is easy to insulate ,before backfill on the inside walls i use 2"styro and pour the slab against this it runs to the footings .

1. 
   DanH | Jan 25, 2011 07:28am | #2

   Not sure how it sits with the code folks, but you can do a slab and then set a row or two of CMUs or concrete brick on top to elevate the plate off the slab.

   Of course, a lot depends on how level the site is.

1. 
   FairviewTim | Jan 31, 2011 05:17pm | #10

   Not sure how . . .

   Hi Dan,

   I've seen it quite a bit around here so it must be allowed. Our code doesn't address it specifically. My main issues with that style are the thermal bridge. I could set the pad back from the structure perimeter and insulate and veneer the step out to the structure edge but I'll either lose space inside or have to build larger which throws off buying standard material sizes and having waste.

   Since you brought this option up, I entertained the idea of using RASTRA or ICFs and modifying them to lip-over the mono slab to get a thermal break. I don't know if the expense id worth it.

   Any thoughts on that? We are on a mountain that experiences high wind gusts at times.

   Tim

2. 
   FairviewTim | Jan 31, 2011 04:56pm | #7

   garage

   Thanks! That's kind of the way I'm leaning but a lot of concrete finishers lean towards the mono pour. I think it's easier for them to finish because they don't have a stem wall to finish around.

2. 
   glacierfergus | Jan 25, 2011 12:56pm | #3

   My garage is a thickened edge slab (5 inch slab, edge is 18 inch by 12 inch).  We sloped the floor toward the doors, but kept the walls at level on 3 sides. To pour it I used 1.5 inch galvanized pipe (father-in-law had it laying around) as screed pipes to set the level, and I used cuts in the pipe to get them to bend so that 3 sides were level, and all the floors sloped away from the walls and toward the doors. The garage door side was a pain in the butt to frame, because the studs from the outside wall to the doors had to be cut a different length to keep the roof line level.  We only sloped about 1.25 inches in 30 feet, so you don't notice the slope, but water slowly runs out the doors.  I don't hose the floor out very often, but parking a wet or snowy car in there allows the water to head for the door. 

   If I was doing it again, I would do footings, wall and pour the floor afterward.  That way I could have all my walls at the same level making framing easier, I could insulate the slab easier, and I could set whatever slope I wanted on the floor without worrying about the walls.  Also, when I hose the floor out the splash would be against concrete instead of a frame wall.  We did it the way we did because it was getting late in the fall and we were worried that we might not have time to get 3 pours done before the ground froze.

   We are also on a VERY stable gravel soil, so there is very little chance of heaving, even though we are in a cold climate (Montana).  If there is a chance of heaving, I would definitely do walls and footings. We are also not heating the area, so insulation was not as important to us.

1. 
   FairviewTim | Jan 31, 2011 04:58pm | #8

   garage

   Thanks for the input. I like your user name. Sounds cold . . . brrrr.

3. 
   Waters | Jan 27, 2011 03:24pm | #4

   Poured Yesterday

   Just yesterday we poured the 20x26 mono slab for my shop.  It's got 3 loops of pex in it for radiant heat.

   I agonized over mono/stemwallsfootings too and went with mono, but going either way has it's benefits and drawbacks:

   MONO

   • Form once--pour once, which was the biggest plus for me

   • easy

   • Heated slab requires r-15 perimeter foam and r-10 in the field, foam exterior then needs flashing and stucco which is kind of a bad detail.

   • another big downer is that downturned slab edges can have a LOT of volume.  A lot of concrete used...

   Footing and stemwalls then slab

   • up to 3 pours

   • more excavating, filling, compacting

   • better insulation detail--you can bevel the foam up to the wall in the slab and have nothing exterior.

   Cheers!

   Pat

1. 
   FairviewTim | Jan 31, 2011 05:01pm | #9

   Poured

   Thanks, Pat. I'm more convinced to do the stem wall approach. I will be heating it so insulation is very important to me.

   Tim

4. 
   junkhound | Jan 27, 2011 03:32pm | #5

   My forge and heavy equipment workshop has 2ft high stem walls. 

   Main consideration was I did not want welding sparks to go skittering across the floor into anything combustible. 

5. 
   Clewless1 | Jan 29, 2011 09:41am | #6

   Dan points out a good option that keeps the mono style inexpensive.  CMU around the perimeter ... easy to tie into the anchor bolts or rebar. Another option would be to make a small second pour of concrete to do the same as the CMU ... whichever suits you best.

   Personally, either way you go, I'd insulate the exterior wall w/ polystyrene and provide protection/flashing to below grade. Since you are doing radiant slab, insulate under as well. With the monopour you end up w/ a bit of a thermal bridge at the perimeter ... no real way around that, I don't think.

   food for thought.