Structure support under fireplace

COamateur

New Member
Feb 10, 2020
13
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.

DBCA0056-AA85-4A0F-B694-EA8E7D3357D6.jpeg 7FFD4139-C287-4955-B79F-5A6D5DF23F5E.jpeg 6CDCEADF-FFA6-4A6D-91F0-AB00A4982BAD.jpeg 8081F12E-4AC3-46E8-824B-C5C939B7E316.jpeg 04E4AE00-7793-4890-9A97-4D8A8BA2E0E2.jpeg 7C918E32-8722-44D5-9007-9602C0A46CA5.jpeg
 
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mark cline

Minister of Fire
Dec 20, 2012
652
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
10,932
Indiana
That’s pretty scary, there shouldn’t be any wood in there at all. It looks charred too!
 
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COamateur

New Member
Feb 10, 2020
13
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
13
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
652
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
652
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
21,947
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.
 

COamateur

New Member
Feb 10, 2020
13
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
13
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
21,947
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
 

COamateur

New Member
Feb 10, 2020
13
Denver
UPDATE!!

I ripped out the tile, brick, and cement under the existing hearth and into the fireplace.

What you see now (at hearth location) is 1x6s sitting on top of a curved barrel arch joist support below.

What you see in the back (of fireplace) is the top of the foundation wall. If you look closely, you can see where the tips of the arch joists sit on top of that wall. Kinda scary...they have maybe 2” on the edge of the wall!

From the bottom of the current joists to the top of the finished floor I have right at 10”.

At this point, I’m not sure if I ought to just rip out the barrel arch completely, as well as the header where the joists stop, sister in some new 2x6s and carry them all the way onto the sill / back of fireplace.

OR leave the header, and just carry new joists off of it onto the sill (instead of the arch).

OR just leave the arch as it is and reinforce with new 2x’s below and then fill with concrete.

Any advice?!
 

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bholler

Chimney sweep
Staff member
Jan 14, 2014
21,947
central pa
UPDATE!!

I ripped out the tile, brick, and cement under the existing hearth and into the fireplace.

What you see now (at hearth location) is 1x6s sitting on top of a curved barrel arch joist support below.

What you see in the back (of fireplace) is the top of the foundation wall. If you look closely, you can see where the tips of the arch joists sit on top of that wall. Kinda scary...they have maybe 2” on the edge of the wall!

From the bottom of the current joists to the top of the finished floor I have right at 10”.

At this point, I’m not sure if I ought to just rip out the barrel arch completely, as well as the header where the joists stop, sister in some new 2x6s and carry them all the way onto the sill / back of fireplace.

OR leave the header, and just carry new joists off of it onto the sill (instead of the arch).

OR just leave the arch as it is and reinforce with new 2x’s below and then fill with concrete.

Any advice?!
You need to take all of the wood out of there and make forms either out of metal or wood that you can remove. Then pour a reinforced slab
 

COamateur

New Member
Feb 10, 2020
13
Denver
You need to take all of the wood out of there and make forms either out of metal or wood that you can remove. Then pour a reinforced slab
But keep the arched joists? So rip out the wood that's sitting on the arched joists and then put sheet metal over them, forming a pan/mold for concrete?
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
21,947
central pa
But keep the arches joists? So rip out the wood that's sitting on the arched joists and then put sheet metal over them, forming a pan/mold for concrete?
No take out any and all wood under the hearth or hearth extension.
 

COamateur

New Member
Feb 10, 2020
13
Denver
@bholler thank you for the help! I'm not sure I understand, though...if I take all wood (including those wood joists), something has to carry the weight from that header (boxed in red in my attached pic) to the foundation wall. Some type of steel joist or channel? I'm not sure how to best connect that to the header. Any thoughts? Or pics you've seen online?
 

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bholler

Chimney sweep
Staff member
Jan 14, 2014
21,947
central pa
@bholler thank you for the help! I'm not sure I understand, though...if I take all wood (including those wood joists), something has to carry the weight from that header (boxed in red in my attached pic) to the foundation wall. Some type of steel joist or channel? I'm not sure how to best connect that to the header. Any thoughts? Or pics you've seen online?
You cannot have wood under any part of your hearth. Some times that means you have to change structure around so it is right.
 

begreen

Mooderator
Staff member
Nov 18, 2005
83,758
South Puget Sound, WA
Here is a thread of a proper, reinforced, poured hearth + extension from the underside after the form was removed. The poster further supported the sides with angle iron.


And here is a sideview drawing. Cleanout is optional. Rebar reinforces the cantilevered hearth extension.
fireplace.png
 

mark cline

Minister of Fire
Dec 20, 2012
652
Cattaraugus, NY
Begreen, being that the OP is putting in a VC stove , is it necessary to pour concrete, etc. for a fireplace, or does he need to provide support for the stove and provide the recommended clearance to combustibles that VC requires? Is there something in the Denver building code that a fireplace needs to be rebuilt to a proper fireplace even though it’s for a wood stove?
 

begreen

Mooderator
Staff member
Nov 18, 2005
83,758
South Puget Sound, WA
The fireplace hearth and extension were never done properly. One does not know how it will be used 10-20 years from now. As built, it nearly caused a house fire. The hearth should be fixed now or condemned as a fireplace. It is unsafe.
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
21,947
central pa
Yes @mark cline (@begreen ; @bholler )...I think that’s the question I’m after. Do I need to transform this into something it never was, or simply provide enough clearance and support for a VC Encore to sit on?

Appreciate the thoughts here!
The problem with just doing it for a stove is that once it is all built and covered up it will just look like a fireplace. In the future no one will be able to easily tell it isn't safe to use as a fireplace. Really at this point it doesn't seem like it will take all that much extra work to do it right. So it makes sense to me to do it properly
 

webby3650

Master of Fire
Sep 2, 2008
10,932
Indiana
We ran into this once on a job. The builder remodeled the room, we put an insert in the fireplace a few years later. The builder had removed the hearth extension, replaced it with a wood framed floor system, then cut the original bricks down and placed them over the wood subfloor. There was no way to know it was installed this way. The entire fireplace looked original to the home. It was a problem and guess who was at fault? Not the builder, or the home owner... the installer was. It was a ridiculous claim!
Do it right, you’ve gotten this far into it. It’s not fair to let someone else take the fall for shady work in the future.