Sagging hearth

[Brian99]

I am looking to install a wood stove on my existing hearth (Jotul Oslo) There is a significant slope from the firebox to the edge of the hearth extension (about a half inch). House is about thirty years old. Haven't noticed any new sag since we moved in four years ago. Construction appears to be self supporting plywood framed out by a few two by 8's that run from the sill plate to the main house beam. Box is filled with gravel as far as i can tell. Chimney was inspected four years ago. an insert was recommended and we had some other repairs done at the time ( waterproofing, new crown etc.) There are settling cracks that run along where the hearth meets the brick facing and firebox. Looks like previous owner filled in cracks with mortar and built shelving below. This looks like it Is supporting the left side but there isn't anything extra on the right.


Wife is not in love with the Vermont stone so I'm wondering if the hearth could be leveled/reinforced by just taking the top stone out, leveling it, and placing a new tile on top. Does this seem reasonable or would we need to rebuild the whole thing from the basement up? No room to add cinder block columns due to boiler placement.

Any thoughts or suggestions would be greatly appreciated.
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[ScotO]

Wow, if the hearth is sagging badly, a set of metal supports may be in order under the hearth area.....from floor to gang joist.

When the hearth sags, it's just a matter of time till you have cracks and problems right on up the chimney, I would think. I'd be getting an honest professional opinion, in other words get someone in that you trust to be honest that has the expertise to give you an honest assessment of what needs to be done.

 

[BrotherBart]

Yeah. Normally those are built like mine. With cantilevered reinforced concrete supporting the hearth. And even with that I sometimes have thoughts of a five hundred pound box full of burning wood falling into the basement.

 

[Brian99]

Yeah. Normally those are built like mine. With cantilevered reinforced concrete supporting the hearth. And even with that I sometimes have thoughts of a five hundred pound box full of burning wood falling into the basement.

Not sure what thy did here. Almost looks backwards. I assume a cantilevered install would have a 2x4 nailed to the joist which would support a sheet of plywood running to the block under the fireplace that could be filled with concrete. Mine seems to have an extra set of block at the sill plate which makes the support run downhill away from the wall.

 

[Nick Mystic]

I'm having a hard time knowing what I'm looking at in those basement photos. In the first picture there appear to be two cables (white and orange) going up through the subfloor. Is that supposed to be the area under your hearth extension? If so, where do those cable come out? If not, then what are we looking at? Then in the third photo are those three 2x6s running along where the front of the hearth extension would be lining up? Are you thinking that this beam is sagging causing the front of the hearth to drop the half inch you mention? If you can clarify this for me I can better understand your problem. I had a similar situation with my hearth extension.

 

[Brian99]

Yes. Those first photos are from below the hearth extension. The cables are coaxial cables that run to the end of the room and to a second floor room. I'm not sure if the the beam is sagging as there is a shelving area built underneath. The plywood sheet under the hearth has a noticeable sag though.

This first photo is under the left side of the hearth. The white dry lock tile is the height of the sill plate. Just to the right of the duct is where four two by fours frame out the side of the hearth. The three boards nailed together are the front of the hearth. The board closest to the wall is a two by four which is the lip the plywood is resting on. The other two by fours in the picture running floor to ceiling are shelves which also seem to be supporting the beam.

Te second picture here is looking from the left side of the hearth to the right underneath the extension. Boiler sits below.

 

[Michael Golden]

Yea it looks like there should be some concern over that. I ain't a building, but there are plenty here that can help your!

 

[Nick Mystic]

That looks like quite a sag in that second photo that you said shows the underside of the hearth extension. I think you are correct in thinking something needs to be done before you attempt to set a heavy wood stove on the extension. Since you say there is a boiler directly below the extension and you can't get any vertical support posts directly under the extension, then it seems like the only other option for support is to put in some floor joists that would run from your cinder block wall perpendicular to the hearth out a distance beyond the extension. Those floor joists would then tie into a new beam you would have to install, again beyond the hearth extension. If necessary you could then put some vertical support posts under that new beam. At any rate, you most likely are going to have to remove the existing hearth extension and replace your sagging subfloor before you do any of this structural work down below. I don't see any way to lift up that sag if you can't get underneath it due to the boiler being n the way. It doesn't look like any sort of quick fix to me.

 

[Brian99]

Thanks for the input. I can across your earlier posts and saw the small blocks under the front legs. Ideally, I'd like to see if I could have the hearth raised, and shored up underneath to get a stable and level area to place the stove will be talking to some masons soon.

 

[Nick Mystic]

Yes, my situation is a bit different from yours. In my case my hearth extension was lower in the front about 3/4" below the level of the back of the extension; however, it wasn't due to the floor sagging. To this day I can't explain why the front is lower, but I do know it hasn't moved in the 12 years I've lived in the house. The living room floor is perfectly level and in the lower level of the house below the hearth extension I have 2x10 floor joists that run perpendicular to my heart and all of those are level. My subfloor consists of two thicknesses of 3/4" plywood. The original owner of the house built it like a fortress! When I switched from an insert to the freestanding stove last year I did not want to put an additional 500 lbs. on the extension, so I slid the stove back just far enough so that the rear legs of the stove would sit inside the fireplace, which is on a foundation that is very substantial. When I positioned the new Jotul F 600 stove I leveled it with those oak spacers you alluded to. So far I haven't had any problems during the six months the stove has been sitting there.

 

[My Oslo heats my home]

Brian, the good part is you have access to the problem. You have room to shore up the sag before it gets any worse and prepare for a several hundred pound stove. I think I would try to slowly remove the noticeable sag over a short amount of time and then frame in some new support to handle both the sag and the new stove weight. With slowly jacking the sag back into place you may hold back any further damage to the brick and mortar.