I think i have a chimney-hearth separation problem - where do i start???

[HHE773]

So I bought my first house in November and have been enjoying home ownership so far. I was looking around near my fireplace and noticed that the hearth appears to be separating from the main chimney structure. (see pictures in link) If i put my finger on the crack and have my wife lightly bounce on the floor in front of the chimney i can feel the hearth moving with the floor signifying that the hearth is being held up by the floor joists. I went down below into the my (finished) basement and can see that the joist near the front edge of the fire place (in the ceiling) appear to be drooping causing a shadow near the wall. I tried to capture this in the photos but you may not be able to tell. I'm a DIY kind of guy and would love to fix this myself if possible. I am wondering where to start or what to tear into to figure out how much of a repair this will require. I figure i will be ripping out drywall down below to see what we are working with. Any advice would be great!

 

[bholler]

Start in the basement with what is (or in your case is not supporting) the hearthextension. I would bet it was built directly on the floor instead of a slab tied to the hearth as it should be

 

[Destructor]

Yup, the inner and outer hearth should have been poured as a monolithic concrete slab. The outer hearth cantilevers out from the chimney and should have had rebar installed from the back of the inner hearth to the outer hearth, totally self-supporting. Rebar in a cantilever slab is most efficient when installed closer to the top of the slab. I bet there is concrete block beneath the brick being supported by the floor alone. Also those mortar filled holes are the work of a sloppy mason, many finish bricks also are available as solid units. I would be suspect of other critical areas of the fireplace/chimney with that hearth construction.

 

[cjgoode]

If your hearth was build like this guys, you are in serious trouble


Kidding aside you have a problem. Do the joists run parallel or perpendicular to the front of the hearth.
DIY, If perpendicular you are in much better shape. You need to jack that floor back up GENTLY across all the beams under that hearth till the gap is gone and floor back to original. Then depending on your structure and where if any cross supports are you can sister joist the existing ones, attach new joists to both sides of the existing ones to make the floor stronger to support the weight. Also add some spacers between the joists under the hearth to keep the joists from twisting at all with the weight.. Same basic concept if they are parallel to the front of the hearth, but the spacers between the joists will be a lot more weight bearing and need to be fastened well and more of them. Strengthening the floor needs to extend well beyond the heart and preferably to any cross supports. I am not an engineer or architect, but the concepts are simple. If you have engineered beans the wooden I beams then you might want some help, I would not attach anything to an engineered beam. But if 2x6's 2x8's etc I have done this many times to fix sagging floors. I have built a T out of 4x4s maybe 4 feet wide and used a car bottle jack, once the top of the T is in contact with all the floor joists and you get some pressure it is very stable, and you can jack in very fine incremental amounts, it can be shocking how little pressure it takes to get it back, as the wood wants to go back. Once again I AM NOT AN ARCHITECT, but a DIY who does everything my self. An Architect/engineer figures out the minimal material to get the job done, I just get extra and go nuts and do sister joists on both sides where maybe one would work.

 

[bholler]

If your hearth was build like this guys, you are in serious trouble


Kidding aside you have a problem. Do the joists run parallel or perpendicular to the front of the hearth.
DIY, If perpendicular you are in much better shape. You need to jack that floor back up GENTLY across all the beams under that hearth till the gap is gone and floor back to original. Then depending on your structure and where if any cross supports are you can sister joist the existing ones, attach new joists to both sides of the existing ones to make the floor stronger to support the weight. Also add some spacers between the joists under the hearth to keep the joists from twisting at all with the weight.. Same basic concept if they are parallel to the front of the hearth, but the spacers between the joists will be a lot more weight bearing and need to be fastened well and more of them. Strengthening the floor needs to extend well beyond the heart and preferably to any cross supports. I am not an engineer or architect, but the concepts are simple. If you have engineered beans the wooden I beams then you might want some help, I would not attach anything to an engineered beam. But if 2x6's 2x8's etc I have done this many times to fix sagging floors. I have built a T out of 4x4s maybe 4 feet wide and used a car bottle jack, once the top of the T is in contact with all the floor joists and you get some pressure it is very stable, and you can jack in very fine incremental amounts, it can be shocking how little pressure it takes to get it back, as the wood wants to go back. Once again I AM NOT AN ARCHITECT, but a DIY who does everything my self. An Architect/engineer figures out the minimal material to get the job done, I just get extra and go nuts and do sister joists on both sides where maybe one would work.

No to fix it you need to take it all out cut out and combustibles underneath reframe the floor around the hearth extension. Then build noncombustible forms and pour a slab that is pinned back to the main hearth slab. Then rebuild the extension.

 

[Nick Mystic]

When I look closely at your photos it appears to me that your hearth extension is pulling away from the fireplace structure, rather than dropping down as failing floor joists would cause to happen. Is it possible that you could shore up the ends of the floor joists downstairs where they attach to the wall. This might be as simple as inserting some posts under a ledger below the joists. Then up in the room with the fireplace and hearth extension you could try using a jack to push horizontally to slide hearth extension back up tight to the fireplace. First, you would need to clean out the gaps well in the mortar joints to allow the extension to move back into place. The tricky part would be figuring out a way to create an anchor point to secure the jack so it would have something solid to push against. If you have a wood floor and sub-floor under your carpeting you might be able to bolt something to the floor. If you were careful you could probably go right through the carpet without damaging it.

 

[bholler]

When I look closely at your photos it appears to me that your hearth extension is pulling away from the fireplace structure, rather than dropping down as failing floor joists would cause to happen. Is it possible that you could shore up the ends of the floor joists downstairs where they attach to the wall. This might be as simple as inserting some posts under a ledger below the joists. Then up in the room with the fireplace and hearth extension you could try using a jack to push horizontally to slide hearth extension back up tight to the fireplace. First, you would need to clean out the gaps well in the mortar joints to allow the extension to move back into place. The tricky part would be figuring out a way to create an anchor point to secure the jack so it would have something solid to push against. If you have a wood floor and sub-floor under your carpeting you might be able to bolt something to the floor. If you were careful you could probably go right through the carpet without damaging it.

That doesnt address the issue of combustibles under the hearth extension. It needs fixed the way i said above.

 

[cjgoode]

bholler Why does the hearth need to have combustibles removed from underneath, if it was one row of bricks and the fire was on top of it I could see it. But how much heat would be transferred under the hearth part with 4 rows of bricks or possible cinder blocks with bricks on them. Or do you think there is a wood structure under one layer of bricks, or does it need to be repined so no chance there is any gap an ember could fall down in a crack. Not being sarcastic at all, just want to hear more details of your reasoning to learn more. to be honest I would not even count on a real slab being under the fire place either to tie into.

 

[HomeinPA]

bholler Why does the hearth need to have combustibles removed from underneath, if it was one row of bricks and the fire was on top of it I could see it. But how much heat would be transferred under the hearth part with 4 rows of bricks or possible cinder blocks with bricks on them. Or do you think there is a wood structure under one layer of bricks, or does it need to be repined so no chance there is any gap an ember could fall down in a crack. Not being sarcastic at all, just want to hear more details of your reasoning to learn more. to be honest I would not even count on a real slab being under the fire place either to tie into.

I'll defer to bholler here for the answer but he's 100% correct in his comments. (And you've answered a couple of your own questions.)

 

[bholler]

bholler Why does the hearth need to have combustibles removed from underneath, if it was one row of bricks and the fire was on top of it I could see it. But how much heat would be transferred under the hearth part with 4 rows of bricks or possible cinder blocks with bricks on them. Or do you think there is a wood structure under one layer of bricks, or does it need to be repined so no chance there is any gap an ember could fall down in a crack. Not being sarcastic at all, just want to hear more details of your reasoning to learn more. to be honest I would not even count on a real slab being under the fire place either to tie into.

Because that is what code calls for mainly. Yes in your case with a raised hearth i really doubt enough heat could transfer through to cause a problem. But now you have a crack right at the edge of the hearth leading directly down to the combustibles underneath. And that can be a big problem so fix it right.

 

[Destructor]

There is most likely framing directly below the front of the firebox/face brick, close to the inner hearth which sees a lot of heat. Normally the framing is boxed out around the outer hearth. A hairline crack is not uncommon at the inner outer hearth junction but you don't want it to open up.

 

[HomeinPA]

What you need to do if you'd like us to give you a more clear picture is to go down in the basement to the chimney and take a picture of the floor joist and subfloor along the base of the chimney so that we can see what is below the hearth extension. Basically lay on the basement floor in front of the chimney and take a picture straight up.

 

[HHE773]

Thanks for all of the comments so far. I'm planning on going down and ripping out some drywall one of these evenings after work to get a better look at whats going on. Once I get that far I can check if the floor joists are sagging via laser level, and can post some more pictures.

 

[Destructor]

Or there is a slab there with little to no reinforcing and it broke away. At this point you're better off without a slab as it would have to be removed in order to rebuild the hearth.

 

[Beer Belly]

I'll be watching.....I have the same issue since we put the Insert in. Our Joist are 2x8 16 on Center....our Yorkie (big boy, 17 pounds) walks by and you can feel the floor flex. It hasn't widened any in the past 7 years, any build up below will need to be engineered around the Furnace and Hot Water Tank.