Floor loading of hearth / stove

[mliiiwit]

I will be installing a 700 lb. Woodstock Progress Hybrid on a hearth I built over an existing floor. My house was built in 1958 and has 2x10 solid pine floor joists with 3/4" solid pine subfloor and 3/4" solid oak flooring, all with no known or suspected deficiencies. I built the hearth on top of the oak flooring as it would have been a shame to remove it, plus I expect the 3/4" oak is adding considerable strength and/or rigidity to the entire installation. What I am not fully certain of is if the combined structure needs to be braced in any way. This area is over a basement and the 2x10 joists are spanning a little over 12' to 2x4 load bearing walls'. The stove & hearth is installed in the middle of this span and the hearth is 60" along the joist spans and 44" across the joist spans (so directly bearing on 3 of the 12' span joists). The hearth consists of 2 layers of 3/4" underlayment plywood screwed together in a 1 foot grid pattern for rigidity, 2 layers of 1/2" concrete backerboard for R value, and 1 layer of 1/4" ceramic tile The hearth is secured to the existing oak flooring / pine sublfoor with #10 deck screws at 9 evenly distributed locations. I expect the oak flooring and pine subflooring are further distributing this load but I am not an engineer. Does anyone have any education/training based feedback on whether this install is structurally acceptable without any additional joist support? With all due respect, I am not seeking any un-educated "I'd do this just to be safe" speculative recommendations. I could easily over-engineer additional bracing myself.

 

[wingsfan]

I had a 120 gallon fish tank and stand on my floor near the center of the house like your setup.I estimate that with all the water and decor in the tank, it was pushing 1000 pounds. I never had any problems. If you are worried you can always put up a stantion post in the basement under the stove and you would be good to go.

 

[Dune]

You alreadly over-engineered it plenty with the two layers of 3/4 plywood. Be sure the joist bracing/blocking is intact.

 

[Stump_Branch]

Whats the spacing of the joists? Ill assume 16 inches. Solid pine 2x10s spanning 12ft has a good section modulas. Not as nice as 2x12s but you get the point. The rule for deflection of a floor is something like 1/3 inch per foot. This is so any drywall ceiling below doesnt crack. living areas are planned as having to meet 40lbs per square foot, sleeping areas are allowed 30lbs. Thats 40lbs is over the whole floor.

Sure you have a point load in near the center of the span, but if your hearth pad is rigid enough your decreasing the deflection rate.

You should be just fine. Homes built back then tend to be built better than todays anyways. Should you have a problem, i doubt youd notice it for a decade or more really. If anything the 2x4 load bearing wall you mention that catches the joists would be the only real suspect worth bracing.

Local building codes apply.

 

[Wade A.]

I agree with the opinions above, you are probably fine. Think of it this way....have you ever had ten or more people in your living room standing together? Think how much weight that equals. Your hearth build up is good and rigid. As it has been pointed out, the thing you most need to be concerned with is deflection over the span. I'm betting you won't have any. OTOH, if you have a drywalled ceiling below it, look for cracks along the seams. If they are present, and you are overly concerned, then yeah, you can shore it up with a jackstud wall below. Not that this is exacly optimum, I know, but it will give you a bomb-proof solution. I'm betting you won't need that.

 

[SteveKG]

I have a similar floor set-up, only 3/4 ply sub and 3/4 pine flooring. On that is sitting a 900 lb. cookstove. No hearth [sits on a plinth]. I have no floor troubles. My joists are 16" centered 2 x 10s running 14 ft or so. Your stove weight will be distributed over several joists.

 

[sksmass]

If you have access to the joists you could take this opportunity to add bracing <u>between</u> the joists. That might transfer some load between the joists. Also keep the joists from bowing side to side. But I don't think you'll have a problem.

 

[jimbom]

...44" across the joist spans (so directly bearing on 3 of the 12' span joists)...Does anyone have any education/training based feedback on whether this install is structurally acceptable without any additional joist support?

In general a 2" x 10" joist 12" on center will span 12' with no problem with the load you describe if decent lumber was used. The variables are member size, spacing, span, and strength of the lumber.

I will run the estimate. The following additional information is necessary: Joist spacing and end bearing conditions. End bearing questions come to mind because it is unusual to find floor joists erected on stud walls in the basement. Often floor joists bear on the perimeter foundation wall and a structural beam on column on footing arrangement. Is this the case in your home? Perhaps the 2" x 4" bearing walls might have been added later when the basement was finished.

The following additional information would be helpful: Any stamps or marks on the floor joists and what those marks read. Is there any blocking or xbracing between joists? Say at midspan or 1/3 span. Is a ceiling nailed to the bottom of the joists to finish a room in the basement? If so, what is the ceiling made of?

Why are you asking? Does your floor bounce under certain conditions or has some part of your home disappointed in some way? Good on you for thinking. That is one heavy stove.

 

[mliiiwit]

Thanks all for the feedback. To answer a few of your questions: The basement ceiling is finished but I believe it is acoustical tiles directly on the joists so probably no contribution to the structure. The joists are on 16" centers and are braced. The only ink stamps I can see look to read "82 PIB CONST", the PIB is questionable as the letters are crammed together in a ball shape. I don't know if that's a grade marking or simply a mill marking, however, the joists are very straight grained and to me appear to be choice old-growth lumber (was anything else available in 1958?).

There are 3 load-bearing walls in the basement which, along with a basement wall, form this central room. This central room is surrounded on 3 sides by additional rooms & utility areas beyond the load-bearing stud walls. All of the surrounding rooms are along the perimeter of the basement wall.

The stove is now installed and it does appear there may be a very slight deflection as a hairline crack has appeared in the grout joint between the hearth surface tile and the wall tile. Not the least bit alarming to me.

By the way, this old shack had a good shaking from the Oklahoma earthquakes last year. It creaked and groaned some but no cracks appeared anywhere. I never expected to feel an earthquake in this part of the world. The wife and I were sitting on the couch surfin when it sounded like strong wind gusts hit the house from all directions at the same time, then it just kept shaking for 15 or 20 seconds. Very interesting experience. The house is well-built, I have no question of that.

 

[jimbom]

...The joists are on 16" centers and are braced. The only ink stamps I can see look to read "82 PIB CONST", the PIB is questionable as the letters are crammed together in a ball shape....

This floor should be good for a 13.5 foot span with a live load of 50 psf, dead load of 20 psf, and deflection limit of L/180. You are good to go, as you already found out.

 

[BlankBlankBlank]

Ask yourself this question - can 4 full size adults stand in the same area the stove would occupy without any un-necessary or noticeable floor deflection, movement, bounce, etc.? You could always add cross bracing between the floor joists to be sure they would not twist under any possible deflection in the floor, though I doubt you would need it.

For my installation, I installed 2x10 cross blocking at various points under the hearth area, figuring it is easy and cheap enough to add it now rather than after the tile has cracked, or whatever. You probably don't need it though. Do the four grown man test or make it six for the fudge factor.