Structural Load Question

[CassMcC]

Hello all! We are contemplating the DIY installation of a fireplace in our living room. We want to do a floor to ceiling stone facade fireplace that is about 6 feet wide with an electric insert.

The house was built just over 2 years ago and the joists are I-joists and are stamped with the following information:
LPI 20 plus 11-7/8
240 MSR NLGA 1650Fb 1.5E R 1/4
They are 16" on center. The wall that we would like to place the fireplace on runs parallel with the joists. The framing and stone for the fireplace we estimate will be around 1,000 pounds.

Are we structurally okay? I am just concerned because the of the parallel design and the fact that the joists span about 20 feet with no support poles under them in the basement. Our builder upgraded the joists to keep the basement as open as possible.

Any input is greatly appreciated as I am no structural engineer!

 

[bholler]

Hello all! We are contemplating the DIY installation of a fireplace in our living room. We want to do a floor to ceiling stone facade fireplace that is about 6 feet wide with an electric insert.

The house was built just over 2 years ago and the joists are I-joists and are stamped with the following information:
LPI 20 plus 11-7/8
240 MSR NLGA 1650Fb 1.5E R 1/4
They are 16" on center. The wall that we would like to place the fireplace on runs parallel with the joists. The framing and stone for the fireplace we estimate will be around 1,000 pounds.

Are we structurally okay? I am just concerned because the of the parallel design and the fact that the joists span about 20 feet with no support poles under them in the basement. Our builder upgraded the joists to keep the basement as open as possible.

Any input is greatly appreciated as I am no structural engineer!

The load should probably be transferred down to the footer. But the basement floor should be ok due to the fact it is pretty much just a veneer

 

[mcdougy]

Sure doesn't sound like its a simple "no problem" I would advise that you try and get your builder back and take a look for you. 1000lbs isn't a herendous load, but still worthwhile to get his opinion.

 

[johneh]

If you were in Canada you would need a structural engineer
to sign off. Keeps the insurance company and the town/city
building inspector happy.

 

[Isaac Carlson]

1,ooo lbs is not a crazy load, but a lot depends on how many beams will support the load and where the load is along the beams.

We put our 1,000 lb stove in our living room, with 16 ft span and it has slowly been deflecting the beams and will need support posts under it.

Can you use fake stone to reduce the weight? They make beautiful foam based stone.

 

[zrock]

no matter where you live you should have a engineer do up the plans and the structural requirements... For the few $$ it may save alot more in the future if done wrong. More than likely your are going to need something below to transfer the weight to the floor below and may have to pour a deeper footing for the weight... Im thinking you are really underestimating the weight. I would guess 2000-3000 depending on the stone facing your using... stove itself will probably be 300-500lbs by itself

 

[peakbagger]

I am not a structural but here are some rules of thumb. Floors generally are designed for live load of 40 lbs per square foot. Live load does not include the weight of the actual floor, its the movable stuff on top of it, that includes furniture and people. The spacing is 16" so for every linear foot of beam its rated for 30 lbs. The beam is most likely capable of carrying more but then something call deflection figures in. Deflection is the amount of sag in the floor between the support points on either end. If deflection is not an issue that same beam with proper side bracing may be good for lot more weight but it makes for bouncy floor. Local codes may set a maximum deflection. The numbers I have used is 1/360 for main floors 1/240 for accessory rooms like attic floors. High end homes may be spec lower deflections to give that nice rock solid feeling. Drywall does not like much over 1/240 or it can crack. Loads bouncing up and down can actually put short term dynamic loads that are higher than then dead loads. Pile a bunch of cartons on the floor slowly and you can considerably exceed the load rating. Remove some of the the "dead loads" and replace it with a person of the same weight who is jumping up and down (live load) and the floor may fail. The problem with minimizing deflection is that trying to reduce it usually means make the support joists taller. There is something called the section modulus for any beam supported between two points. The section modulus is also called "I". If you look through the I joist engineering info tables there will be list of I values. The standard I formula for a rectangular beam is 1/12bh3 where B is the width of the beam and H is the height. The I joist (note the clever use of I in the name to hint that an I joist has a high I value) is going to have a more complex formula but looking at the equation you can see that adding width to a beam doesn't get you much because it is multiplied by a fraction while adding some height makes a big difference as its cubed.

So your proposed stove is going to exceed the load rating of the floor, its wide enough that the load is spread out over two beams the 30 lbs per linear foot is now 60 pounds per linear foot. It also makes a difference where along the beam is located, if its at the center between the supports its lot worse than over near the sides. Even if you spread the load out between three joists my guess is you probably are still deflecting too much.

So the options are pretty simple in theory but not so easy to implement

Reduce the span of the beam. Ideally stick a post under the beams that support the stove down to a footing in the basement and be done with it. If you cant put it directly under the stove put some off to the sides. Shortening the span between supports really reduces the deflection. It varies by the square, so double the span the deflection goes up 4 times (2squared) Cut the span in half and the deflection is reduced by 1/4. (1/2 squared).

Add more I joists between the existing ones, cut the spacing between the joists to 8" and you double the load you can have on the floor at the same deflection. Its usually a PITA as there are usually pipes, wires and crossbracing in the way plus getting the beam up on the supports is tough due to lack of clearance on either end. Make sure if you do this that the cross bracing is put back in place as other bad things could happen.

Add height to the floor joists. Especially with I joists that is something best left for a structural engineer. A general concept a structural engineer may do is add some height to the beam below the lower flange of the I joist by adding a a thick wood or plywood strip to the bottom of the beam, maybe 4" thick, then cut some structural plywood strips to the new height and slide the plywood up between the joists and glue and screw the plywood to top, bottom flanges on both sides of the I joist and its added lower section. The tricky part is recalculating the I value to see if you increased it enough that the 1/360 criteria is met.

The other approach is put some steel in. Steel bends a lot less under load than wood (roughly 30 to 1 ) if the I joist was made out of steel the load rating would be much higher Replacing a joist is not easy so the alternative is box out the beam with steel similar to what I described above without the added depth. This is tough as steel expands and contracts at a different rate than wood so getting a permanent bond between the wooden flanges and the steel is difficult. I have done this method on standard 2 by lumber and just predrill holes in the steel plates, goop up the surfaces, then bolt right through the wood. Not so easy with an I joist. It really stiffens things up.

Note this all may be moot if the local codes require a structural engineer to sign off. he has a lot more tools than I do. There are also seismic codes that complicate things

(Note earlier in my career I designed an elevated railroad trestle inside a building supported from a lower floor for my employer. Its been close to 35 years and its still standing. I designed it for two railroads cars on top of each other( I put in plenty of extra steel)

 

[Isaac Carlson]

Peakbagger is spot on and knows what he is talking about.