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Discussion Starter · #1 ·
Hi all,

I'm going to be framing a natural gas fireplace on a basement slab. This will eventually be covered in stacked stone.

The basement walls are all floated at the bottom. The fireplace is to sit 6-8" up off the slab so I'll be building a platform for that.

My question is...

I don't think it's wise to float the bottom due to weight and this platform. So I was planning to float at the top by leaving the top plate 2" short and driving a spike up into the floor truss. However, I'm concerned about lateral load once the weight of the stacked stone is put on. Will the weight of the stone want to "pull" the framing forward and is there a chance those spikes could pull loose or bend?

Anyone have any suggestions on whether this would work, or alternatives?

Thanks folks!

Shane
 

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Discussion Starter · #3 ·
No idea what you mean by floating the bottom.
'round these parts (said with thick western accent, but actually in Saskatchewan, Canada) basement walls are "floated" due to the expansive soils that can cause slab heave. To avoid having the basement wall framing transferring that heave to the floor joists above and/or buckling your drywall, walls are floating most commonly at the bottom like this:

Top plate
Stud
Bottom Plate
2" space
Floor Plate

Then a hole is drilled through bottom plate, and a spike driven through that hole and into the treated floor plate. This prevents lateral movement, but allows the bottom plate to slide up and down on that spike.
 

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Interesting, we don't have to worry much about frost heave around here with our 18" frost line, but I'll give it my best shot. If you float the top and the slab were to heave then the entire fireplace will move, which can cause damage to the brick. The way I picture it is you need to stick with floating the bottom and add something in the ceiling to give the fireplace enough support for the brick. I would probably double up the ceiling joists where the fireplace connects then add some Simpson straps in there to make the connection. It's kind of like when a suspended range vent is specked out, they tell you to double up the ceiling joists to take the weight of the vent.
 

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Discussion Starter · #5 ·
Interesting, we don't have to worry much about frost heave around here with our 18" frost line, but I'll give it my best shot. If you float the top and the slab were to heave then the entire fireplace will move, which can cause damage to the brick. The way I picture it is you need to stick with floating the bottom and add something in the ceiling to give the fireplace enough support for the brick. I would probably double up the ceiling joists where the fireplace connects then add some Simpson straps in there to make the connection. It's kind of like when a suspended range vent is specked out, they tell you to double up the ceiling joists to take the weight of the vent.
The way I'm thinking to do it means the brick would all move WITH the fireplace.
 

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FreshConst said:
The way I'm thinking to do it means the brick would all move WITH the fireplace.
Maybe, but you couldn't fasten your mantle to the wall the way you explain it. You won't necessarily get even uplift either, I've seen slabs crack and slope all different kinds of direction.
 

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Discussion Starter · #7 ·
Maybe, but you couldn't fasten your mantle to the wall the way you explain it. You won't necessarily get even uplift either, I've seen slabs crack and slope all different kinds of direction.
That's correct. The wall is sheeted behind already anyway and I doubt it would line up with studs behind anyway. I could open that wall back up since it will be behind anyway, but I'm not planning to unless necessary.

But yes, the way I'm envisioning would be adhesive on the slab and spiked into the floor joists. No connection at the wall because you're right, IF it did move, connecting to the wall would defeat the whole purpose of floating it.
 

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It might work, it just sounds like a risky way to do it. If you wanted it done 100% the best possible way, I'd say anchor it solid to the ceiling and anchor it to the wall however you can, then float the bottom like everything else in the basement.
 

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I became familiar with this float thing when considering building along the front range area north and south of Denver. Expansive soils everywhere, and those Centennial staters loves them their basements. Finished basements abound.

Using tall baseboards and sheetrocking down to the bottom of the floating plate was easily understood as a concept, in that the floor can heave up, but I got to thinking about what happens at the doors, which are fixed to the upper fixed parts of the rough frame, with their jamb legs and casing legs resting down against whatever is attached to the slab.

So, when the slab heaves up, what happens?

This fireplace thing, I'm thinking it through, and might prefer it down on the slab, and the float parts up top.

People water their foundations out there, during extended dry periods, to prevent the kinds of foundation problems that can come from soil shrinkage.

It is like Goldilocks and the three bears. Not too hot, not too cold. Or for your soil under and around your foundation, not too wet, and not too dry.

Just right.
 
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