And yet another, but different, hearth build scenario...

[delp]

Unlike most folks, I need to build my hearth up from “thin air†to meet the top of the wood floor; my situation is not one where I’m building up from combustible floor surface.

I’m asking for feedback and input from this keen-eyed group.

My basic concern is the strength of the bridge/deck that I need to build to span the empty space under my hearth. I have wood 2 x 9 framing the perimeter on three sides. I looked at the steel studs at home depot, but they are thin, 25 gauge steel, and I’m not confident in their load bearing strength. Do note that the Englander 13 will sit mostly within the firebox, which consists of many, many feet of dirt/stone/rubble. I plan to pour concrete in what is now the dug out firebox floor to bring it level with the wood floor and the hearth pad I need to build, less tile thickness.

The idea is to frame the void with wood 2x4’s that would work as joists spanning and bridging the void, placed perpendicular to the face of the fireplace, and then build up a sandwich of materials that will conform to the R2 value required under the 13NC.

Here’s the sandwich layers I’m thinking (bottom up):

2x4, 24guage sheet metal, Hardieboard, two layers of ½ Micore 300, Hardieboard, stacked spacer strips to create an air layer as well as to build up height (I’ll have about 3 ½†of space for the “sandwichâ€), Hardiebacker, thinset and, finally, tile.

Attached are photos of the void I’m dealing with. Even though my primary concern is strength, if I use wood joists then I want it to be as non-cumbustible as possible from the top down,

Comments? I’m all ears!

 

[SKIN052]

Good luck with that. In my opinion, frame out the void with the same framing as the rest of the floor. I would then add concreat board to become level with the rest of the floor and then build a suitable hearth so would like.

 

[fishingpol]

Use joist hangers for your 2x's and toenail them in. Construction adhesive on top of the joist and 3/4 ply to start. Build up from that. Screwed and glued makes a rigid base. Did that for my hearth tile re-build and no cracking whatsoever. My stove does not weight that much though.

The hole reminds me of the one I had in the floor. Kids got a kick out of it looking into the basement.

 

[jimbom]

Why not use one concrete slab from the hearth out to the wood floor. Form the void for a 4 inch thick slab. Tie the rebar layer into the bricks and into the joists on the other three sides. Put the layer of bar in the bottom of the slab with one inch of concrete below the lowest bar. Place and finish the concrete and keep it moist on top with wet towels or burlap for four days. After four weeks take out the props and strip the lower form. No combustible material below the slab. Single reinforced surface for finish materials.

 

[delp]

fishingpol - yup, stiffen the frame up with 3/4" ply; a better idea than the sheet metal

jimboM - not sure that I can take that on, although it is probably the best idea. i'd have to hire that out, and i guess it's worth getting some quotes.

thanks for the input

 

[Wood Duck]

I don't understand what the sheet metal is for. I don't think it is needed, and doesn't add any insulation for the wood joists below. I think the idea of steel joists makes sense - why add combustible material if you have options? If you are concerned about the strength of the steel, check the rated strength from the manufacturer and compare to a wood joist. For a small space it won't be a big expense to add extra joists for factor of safety and peace of mind. I like the idea of constructing entirely out of non-combustible materials.

 

[delp]

Thanks, WoodDuck, for your thoughts. Yes, my preference is all non-combustible, but I've done very little work with steel studs and am more comfortable building with wood. Since most people seem to build up their hearths with wood 2x's, I figured that whether I build up, or down, then wood joists would be okay. I'd need to rent a chop saw and find 16 gauge studs --the home depot stuff isn't really rated for more than walls with sheet rock. In fact, I'm not sure that any studs should even be used as joists...I'm not sure about a whole lot of critical stuff that falls in the arena of an engineer. It's true that the span is not very big and that, as usual, I'm probably over thinking all of this. Just want to do it as right as possible with the limited resources available to me, i.e., knowledge, money and people power.

 

[budman]

Why not use one concrete slab from the hearth out to the wood floor. Form the void for a 4 inch thick slab. Tie the rebar layer into the bricks and into the joists on the other three sides. Put the layer of bar in the bottom of the slab with one inch of concrete below the lowest bar. Place and finish the concrete and keep it moist on top with wet towels or burlap for four days. After four weeks take out the props and strip the lower form. No combustible material below the slab. Single reinforced surface for finish materials.

This is the proper way to go.

 

[maxed_out]

+2 for Jimbo's concrete slab idea. Pour the concrete so you can finish the floor height the way you want it. Ours finishes (tile) flush with the rest of the wood floor. No toe stubs! Strip off the forms and you'll have no combustables what so ever. You'll sleep better.

If it was me, I'd cut in an outside air duct now in case you ever want to use it. our stove has an OAK and it works for us.

 

[Wade A.]

This might just be me...but as long as your hearth joist band is 9", I see no reason to take it down to 2x4's. I'd at least go up to a 2x6 for the framing. That way, you'd never have to worry about deflection and cracking your tile. And this definitely would be just me....I'd stick to wood framing. A concrete job is heavy, messy, fussy and gives you no real advantage over a wooden frame that I can see. Your chance of failure is also much less AND wood is reversible should you change your mind our your plan.

Assume you've run the numbers on your build-up to comply with the R requirements for your stove? Sounds like though, with 2 layers of micore alone, you should have a high margin of error.

 

[fishingpol]

I think the layer of sheet metal mentioned is ember protection to prevent a stray ember from falling down a potential crack and hitting wooden framing. With the layers of sandwiching mentioned, it would probably not happen anyway. You would have to have a substantial crack through all layers.

 

[Wade A.]

More of a radiant barrier to reflect heat...at least that was what I was thinking when I included it in my hearth. Cheap insurance and no problem to throw it in there. Get you some rollled roof flashing, light gauge.

 

[delp]

Thanks everybody.

The sheet metal thought was more about ember protection but, as you said, fishingpol, it would take one hella-crack for an ember to get down through the proposed sandwich.

I've been all in my head about this slab idea, but it's something I just can't do. I'm flying solo, weight about 103lb on a good day -which is less than double what one bag of cement weighs...making the forms, jacking it up from the basement, rebar...can't go there. I did call a couple of creative cement people but I doubt I'll hear a quote of under $500 bucks for this.

Again, FP, I think your idea of using 2x6"s is smarter than 2x4, especially since my concern is about weight bearing. If I build that sandwich they way I'm thinking (after reading every possible thread on the matter on this forum), I think those 2x6's will not feel the heat. And, if after the first year, there is an issue, I can take the dang thing down and go the cement slab route. I just want to get the stove in place already!

 

[G-rott]

JomboM and budman nailed it.
Totally non combustible and it will leave no question if you change stoves(hearth requirements) later.

Really that much concrete can be mixed in a wheelbarrow and placed by hand.
You can do it, you will find lots of help here.

Garett

 

[SnapCracklePop]

I would frame with 2 by 6s, top that with 3/4" plywood, two layers of micore, tile. Plus, I'd put vertical braces below, assuming that there's room for them down yonder.

And, I'll offer to come and help you.

I have a chopsaw, Sawzall, levels, big-azz hammer, etc., from various Habitat for Humanity jobs I've done.

Shoot me a PM and we can work out the details if you want my help.

Nancy

 

[delp]

Nancy, you are a 100%, true Mensch! Next time you're in Pittsburgh, let me know, 'cause I'd love to take you out for food!

I went out a bought all the 2x'6's and lag bolts and assorted fasteners yesterday, but I'm going to wait and see if one of the cement people can come and give me a quote before I start to build...to be continued...

 

[SnapCracklePop]

It so happens that I will be in suburban Pittsburgh tomorrow. The Somerset County Community Band (in which I play drum set) is performing at the Three Rivers Festival at Upper St. Clair High School.

The festival band starts off at 2:30, and we play at 3, followed by a few other bands. Cookies and schmoozing afterward.

If you want to hear some great music, stop by. And, of course, look for me.

A-one and a-two and a...

Nancy

 

[delp]

Google maps says, 26 minutes. I'm gonna try and make this!

 

[Joe in MI]

I am a complete novice when it comes to building fireplaces, so take this for what its worth (which may not be much)

I always look at a project like this in this way, "If I were building this house right now, and I was planning on putting my stove here, how would I frame and build the floor in front of the chimney?" I doubt very much that anyone would frame the floor under the stove in thinner joist material than the surrounding floor. I am a little confused about what exactly you are doing here. Are you trying to get a certain thickness of fireproof material and have it come out perfectly flush with the wood floor? I guess if that's the case, I can kinda see where you're coming from. I would then agree that 2x6 framing with 3/4 plywood and then your "sandwich" on top of that.

I am a big fan of "simpler is generally better" though. Unless a raised hearth is totally out of the question, I would just build up the floor to match the old joists and subfloor, and put your hearth pad on top.

Also, have you considered the implications of what you are planning to do on any future improvements? For example, if you ever decide you want something different on the floor in that room, you will have to either perfectly match the floor level of the hearth, or have a sunk-in hearth. I would guess that you will never match the thickness of that old floor without some custom planing.

It just seems like building the floor as it would have been when new and building on top of it would give you the most flexibility for hearth shape and any future projects.

Again - just my 2 cents, and maybe not worth that much

Joe

 

[delp]

Joe, believe me, I appreciate all cents and sense folks are willing to share, so thank you.

The depth thing is definitely about bringing the hearth flush with the wood floors. I have no sub-floor, just true 2" x 9 1/2" joists with 7/8" t&g southern pine floorboards; this is true throughout the house, which is a brick row house from 1896. Since the fireplace is a huge triangle that sticks out into the middle of the floor space, I think it best not to have a raised hearth. A more perfect tripping hazard could not be better planned.

I appreciate your two premises: "simpler is generally better," and "if I was building the house right now." The latter is out of my league and financial reach and the first is inherently attractive. What I removed was a huge, 2 1/2" x 5' x 24" slab of slate that is broken into four pieces (was like that when I bought the house). Under the slab of slate were 9 5gal. buckets of rubble, dirt, rock, and some great old marbles! Holding up all that rubble and slab are 1" thick slabs of wood resting on a ledge nailed to the framing joist and on the brick and stone fireplace structure.

Several folks here have recommended a concrete slab, and I agree that this would really be the best solution. However, I do not have the rebar tying and anchoring skills necessary to build the thing as it should be. I got a quote of $525 today from two concrete guys off Craigslist... I have another, more artisan, cement guy coming on Monday and do not expect that his quote will be less than the CL people. All that to say that the concrete slab idea is fading toward the "no can do."

So, it looks like the 2x6 framing + 3/4" ply + non combustible sandwich will be what I end up doing.

 

[Joe in MI]

If it makes you feel any better about your decision, try to remember that the structure that was there before was built to literally build a fire on top of. There's a big difference between that and having a fire in the stove.

I'm with you on the tripping hazard. My hearth (still in the planning stages) will be higher than the surrounding floor by a couple inches, and I can see the value in flush-with-the floor. With no subfloor, though, I guess one of my points would still bear thinking about (for me at least). ANY future floor in that room will have to be installed ON TOP of your existing floor. Of course, if you were re-doing the entire room, it wouldn't be a huge deal to chip out that little bit of tile and add some cement board to bring the level up to the new floor.

Make sure you post more pictures, or we will assume this never happened, and you're just living some bizarre internet fantasy life........