Structure support under fireplace

COamateur

New Member
Feb 10, 2020
6
Denver
Hey all!

I removed our old fireplace insert in exchange for a VC wood burning stove. Very excited about it, but after having a chimney professional take a look, he suggested clearing out the bottom brick and cement (which was all falling a part). I demo’ed it all down to the wood joists below and now I’m curious as to the best way to support it going forward.

Do these wood joists look to be supportive enough? (I believe it’s called barrel arch support). Is the best strategy to just fill with concrete and then concrete board (I would like to do tile)?

I would love any observations you all have from seeing these pics. Thanks so much!


PS the bricks along the back/bottom are the first row of bricks sitting on top of the foundation wall.

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Last edited:

mark cline

Minister of Fire
Dec 20, 2012
637
Cattaraugus, NY
To add some additional support from below, I would screw 2 or 3 - 2x6 across the width of the barrel arch to tie all the floor joists together. Be sure to span at least 2 floor joists on either side of your arch . Then go ahead and fill in the space to level with concrete and a pour in floor leveling compound , being sure to fill all voids, then your concrete board.
Then proceed to your final surface of tile.
 

webby3650

Master of Fire
Sep 2, 2008
10,812
Indiana
That’s pretty scary, there shouldn’t be any wood in there at all. It looks charred too!
 

COamateur

New Member
Feb 10, 2020
6
Denver
To add some additional support from below, I would screw 2 or 3 - 2x6 across the width of the barrel arch to tie all the floor joists together. Be sure to span at least 2 floor joists on either side of your arch . Then go ahead and fill in the space to level with concrete and a pour in floor leveling compound , being sure to fill all voids, then your concrete board.
Then proceed to your final surface of tile.
Thanks so much! That’s exactly what I was looking for. I think I’m going to continue pulling out the tile in front and expose the entire barrel arch joists and see what I can do to reinforce all over.

any recommendation on what building material should go over the supporting arch joists first? (To give something for the concrete to sit in). I’d like to avoid wood
 

COamateur

New Member
Feb 10, 2020
6
Denver
That’s pretty scary, there shouldn’t be any wood in there at all. It looks charred too!
You’re right! It’s definitely charred! No idea how it was used over the last 135 years, but probably coal + wood burning inserts at different times. It looked like different (albeit thin) layers of concrete over time too. My guess was originally it was wood over the joists, and then just brick and lime.

what would you recommend to place over the joists so I can create a cement bed?
 

mark cline

Minister of Fire
Dec 20, 2012
637
Cattaraugus, NY
With a sawzalll, cut all the wood subfloor out . Then you can put in piece of sheet metal or even fire rated drywall on top of your 2x6 . When you screw down your 2x6’s , start at the wall and work out . I would use about 8 - 2x6’s from the wall out, then lay in your sheet metal or drywall then a light weight concrete , then a pour in floor leveling compound. Tile on top to finish. If you can use 8 ft long 2x6’s , that would hold a truck.
 

mark cline

Minister of Fire
Dec 20, 2012
637
Cattaraugus, NY
Send us more pictures when you cut out the wood so we can see your progress.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
20,649
central pa
You need to form and pour a proper hearth slab. And either do it with metal forms or wood forms that can be removed.


It is all laid out here.
 
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COamateur

New Member
Feb 10, 2020
6
Denver
You need to form and pour a proper hearth slab. And either do it with metal forms or wood forms that can be removed.


It is all laid out here.

Very helpful @bholler! Much appreciated! Probably a silly question, but I'm new to it all: what's the difference between the "hearth" and "hearth extension"? I see where the hearth needs to be at least 4" thick, and the extension 2" minimum. Is the extension just everything in front of fireplace opening?
 

COamateur

New Member
Feb 10, 2020
6
Denver
Very helpful @bholler! Much appreciated! Probably a silly question, but I'm new to it all: what's the difference between the "hearth" and "hearth extension"? I see where the hearth needs to be at least 4" thick, and the extension 2" minimum. Is the extension just everything in front of fireplace opening?
Google is our friend. Just looked it up — I think my last statement was accurate. But if I'm wrong, please feel free to correct me!
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
20,649
central pa
Very helpful @bholler! Much appreciated! Probably a silly question, but I'm new to it all: what's the difference between the "hearth" and "hearth extension"? I see where the hearth needs to be at least 4" thick, and the extension 2" minimum. Is the extension just everything in front of fireplace opening?
You got it. The hearth is the firebox floor. The extension is everything infront