I’ve just picked out a stove and placed a deposit on it. Soon, we’ll have a new Woodstock Ideal Steel living here. However, that means I now have to think about a hearth (the stove we thought we were going with until recently needed ember protection only). The problem I’ve got is that the floor where the stove will be installed is VERY flexible! It’s far, far too flexible to put down any kind of brick, ceramic, or other masonry without it quickly cracking. I’ve looked at some commercially available hearth pads that don’t involve stone/ceramic on the internet and they are all god-awful ugly. The requirement for the Ideal Steel is a R0.41 pad. What can I use that will put up with the floor being so flexible and doesn’t look like something made from cheap vinyl tile?
I would feel better if I either shored up the joists and/or secured the subfloor to the joists before putting that kind of weight on a flexible floor. Then, you could do any kind of hearth you wanted too
Congrats! You'll love this stove. Can you describe in greater detail what you mean by "flexible floor"?
Basically the house was built before code was enforced in this county so it never had to pass inspection. The floor joists are 12" chord engineered I-joists under a 3/4" plywood subfloor. The joists are 22" on center. This just baaaaaaaarely meets guideline minimums for the loading of the I-joists. The result is that the floor flexes a lot because the 3/4" ply is spanning the 22" in each bay (which it doesn't really like) and the I-joists themselves are carrying just about all the load they can. The outside ends of the I-joists are connected to the rim joist using joist hangers and all that bears on marine plywood-faced SIPs, so the foundation itself isn't as rigid as in most construction. In doing research about what types of flooring I could use here when I first moved in, I found out that this is way too flexy for any sort of masonry. In fact, if you jump and deliberately land hard, you can actually feel it's slightly bouncy. I already planned to add additional 2x12 traditional wood joists in the middle of each bay that the stove will set over plus one bay to each side in order to cut the span down to 10-ish inches per bay rather than the existing 22" just to carry the load of the stove itself with a little more safety margin. I still don't expect this to make the floor rigid enough to avoid cracking grout, tile, or stone though.
I don't think I would run another joist down the middle of the joist space. Takes away any future use of that space. Maybe you could strengthen the stove area only by adding some crosspieces in the joist spaces? Of course, this also would prohibit and block off the use of the joist space, but you can remove them in the future. If you are set on adding the 2X12's, consider to add them flush next to the existing joists. Scabbing them onto the already existing joist will leave some space in each one for future use. Do you have a basement? This would make the project better for you; you could always add a floor jack to the area immediately below the wood stove.
Build to minimum specifications and you get what you have. It is good for the construction company that is saving costs but not for the homeowner. Your idea of adding additional joists is a good one. What you have to know is what the outside rim is constructed from; can you use joist hangers and add the additional 2X12s? You could also look at getting additional engineered I-joists and add them. The engineered I-joists are good; it is what allowed the builder to use 22" OC. The 3/4 " plywood floor should handle the load once you have reduced the span between the joists; this is probably true 3/4 inch and not the new reduced sized 3/4 inch.
What in the world would you want that space for in the future? Any utilities/duct work that needs to be there should be there already. I would think that it would be more important to make sure that you keep that 500# stove on the ground floor and not in the basement. I would absolutely add another joist in the middle of that bay and maybe the bays next door too. I can't imagine how much a 22" span flexes. We have a storage area at work that has 3/4 plywood thrown down over joist 16" on center and even that bows quite a bit when I (6'4"-250#) step right in the middle of two joists. Once you have the framing to support it, then you could do a proper hearth with the material of choice. Yup ^ ^ ^
You'd be amazed how many times you go back to use a joist space for adding something else only to find that sometime in the past, someone used an easy quick fix to a problem without considering the future. The floor will strengthen up by scabbing a joist onto already existing joists. Must be a reason why I keep seeing contractors strengthening floors that way and not down the center of the joist space.... But, it all boils down to personal preference, right?
I would agree with cross blocking. It would ideally be the same joist material. It should be hangered. You wouldn't be able to use the standard top flanged hanger, so you would need web stiffener to back the hangers to use a face mount hanger. The plus is that the web stiffener would add strength, and cross blocking would keep the joists from deflecting adding further strength. This is exactly what we'd do in a high load area during new construction, except we'd use top flanged hangers prior to sheathing. Web stiffeners may or may not be used depending on engineering requirement.
In this case, going down the center is going to be better than sistering a second beam to each joist due to the fact that 22" is really an unreasonable distance to ask the 3/4" ply subfloor to span. Sistering the joists would make the joists stiffer but do nothing for the fact the ply is unsupported. I'm also not worried about adding extra material due to the fact that I'll still have 10" wide bays if I HAVE to do something but also since there's absolutely no reason to ever add any large utilities in this area because it's just the corner of the garage (below) and great room (above). There's nothing you could put over here other than electric or data.
Just offering alternate suggestions Will. As in every case, the homeowner is the only one that ultimately makes the decision, right? FYI, at my cottage, I have 2X6 on 24" centers with a single layer of 1/2" plywood. Under the stove area, I just cross braced for extra strength and never had any issues with spongy or bouncing. Also, welcome aboard!
Idk what a ceramic tile's R value is, mutt if you used flexible mastic, small tile, and epoxy grout it should be able to handle the "flex" in your system. Combine all that with backer board and I bet your there.
Durock itself is enough R-value so yeah I should be good. Not being a mason, I had no idea about flexible mastic being able to isolate the ceramic/stone from at least some movement in the substrate. Thanks!
i would use tile smaller than 6" with this situation, The mastic like this would be flexible enough that they shouldnt pop, and small tile are more resistant to breaking and cracking than larger tile. Considering you wont be walking on it i wouldnt be too worried. BTW, Contractor for 25
