Building a hearth - floor strength issues?

[The Dali Lima]

I am going to be starting the hearth tomorrow and I was readingup on a few threads here and I am starting to get nervous about the sheer weight that I'm going to be placing on my joists. I am planning on a 60x60 (or so) inset hearth. I'm going to rip up the oak flooring and possibly the plywood subfloor to put down a few sheets of durock and then tile. Will this be too much stress on the joists? The durock, tile, and then the 400+ lbs stove seems like a lot! Just curoius.

thx!

 

[fossil]

Invite about 8 people over, offer them drinks, and have them cluster tightly together in the hearth location. If they don't fall through the floor, you're good to go. Rick

EDIT: Not having plywood (~3/4") beneath the Durock is not a good idea...you need the strength of the plywood, as Durock isn't a structural flooring material.

 

[woodconvert]

I'm going to rip up the oak flooring and possibly the plywood subfloor to put down a few sheets of durock and then tile. Will this be too much stress on the joists? The durock, tile, and then the 400+ lbs stove seems like a lot! Just curoius.

What size joists do you have?. Without further info i'd say you probably won't have a problem with weight. That 400+ pounds isn't sitting on one joist but it's distributed over multiple joists. If two 200+lb people can stand next to each other in your house without falling through your floor then 400+lbs over 25sq ft aint gunna either. That's really not that much of a load.

 

[woodconvert]

ooph...Fossil beat me to it.

 

[Adios Pantalones]

You put far more stress per square inch on the floor walking on it. If the hearth weighs 200#, and the stove weighs 400#- that's only the weight of 4 skinny people. I'm sure that you would not think twice about 4 people standing on that area (as per Fossil's suggestion).

 

[begreen]

Fossil hit the nail on the head. You definitely want something stiff under the cement board to stop flexing. We used 5/4 plywood in our bathroom and after 7 years, including lifting and raising the house, there is not even a hairline crack in the tiles. (Lots of them elsewhere lol). 400# is no big deal. It's distributed over a large area.

 

[The Dali Lima]

Thanks for the replies. The plywood will likely stay... we want to keep the floor flush with the existing oak, so I'm not sure how much Duroc I can lay once you add in the tile.

Thanks for relieving me of my worry - you are correct... 600 - 800# over 25 sqyuare feet really isn't that big of a deal.

 

[The Dali Lima]

By the way - what is a normal hearthpad (that you buy pre-fabricated) made out of?

 

[woodconvert]

Thanks for the replies. The plywood will likely stay... we want to keep the floor flush with the existing oak, so I'm not sure how much Duroc I can lay once you add in the tile.

If it's not possible to keep the hearth floor flush with the existing oak you could make an angled border to make up the difference and you wouldn't have something to trip over or stub your toes on. It's an option to think about.

 

[zionadams]

The Dali Lima" wrote: Thanks for the replies. The plywood will likely stay... we want to keep the floor flush with the existing oak, so I'm not sure how much Duroc I can lay once you add in the tile.







What you wrote about matching floor heights got me thinking..better to use the duroc, at least one thickness. If you can lay a heat barrier membrane below the duroc then that one layer might be all you need. Having said that, I can't give you a brand name for the heat fabric/barrier. Maybe someone in the construction trade will chime in. The idea for beveling the outside edge was a great safety option. It could be a nice detail in the project too.

Have fun with the hearth. I needed a chiropractor after building ours. LOL

 

[jrousell]

there is a bit of a difference betwene the live load of people walking and the dead load of the hearth . but that said-- most likely you will be fine. but it would be better not to asusme..

What size are the joists now? Is teh hearth goign to be located over or near a weight supporting wall beneath it? what is the span to the nearest suporting wall/post ( underneath)?


if it is undersized there are lots fo options... Is the floor cavity exposed form below? If so snap a picture and post it for us...

 

[fossil]

OK, invite about 8 dead people over and have them lie in a heap where you want the stove. You won't have to offer them drinks. If the bodies don't fall through the floor, you're good to go. Rick

 

[trailblaze]

wow... hahah...

any way, no need to rip anything up...

i made my hearth like this... the original floor consisted of 2 layers of hard wood floor over the joists, i then built a 2x4 frame with inside frame supports for airspace, laid a 3/4 inch plywood down, then 3 layers of durock with quick set, then about1/2-3/4 inch of mortar with 1.75-2 inch thick natural stone, then my 475lb stove.... the floor still holds strong!! my joists are 12" centers though (old home, built to stand)

 

[Elfin]

I concur with the advice posted here... the load isn't that much, and definitely use the plywood for a base under the concrete board... for the primary purpose of providing proper support for your tiles.

Regarding pre-fab hearth pads... yeah, I've tried to figure out what they are made of with close examinations of floor samples. The ones I've managed to get a close look at seem to be little more than mdf under the tile top. I'm sure they aren't all like that, but the ones I've seen I haven't been too impressed with.

 

[begreen]

This old farmhouse has stood through storm, earthquakes and even my terror raising it 3 ft.. Done that for 80 years with floor joists 24" on center, give or take a few inches. Built with local wood, they used what they had. FWIW, putting 800#+ of hearth and stove on these timbers didn't seem to even be noticed.

 

[G-rott]

You have some options for keeping you floor level if you have access from below and depending on the hearth r-value required. Post some specifics and maybe even a picture(we love pictures) and we can be more help.

Garett

 

[trailblaster]

I have a 150 saltwater tank covering only three joists and the tank with water and 200lbs of coral weighs over 1500lbs and I have no problem.

 

[jbrown56]

Steve,

I know I'm late in getting in on this but once you remove the hardwood, you'll be left with a 3/4" depression. You can then add 1/2" cement board over the existing sub floor, thin set mortar and tile. This will leave you 1/8" over the existig hardwood. It's plenty strong enough.

Jim

 

[Elfin]

For any type of application of floor tile, you do want to supplement your subfloor with a layer of plywood, since cement board has absolutely no structural strength. Especially with a heavy stove on top, the tile is going to be subject to cracking if applied directly to to the subfloor.