For the nerd herd: Open Web Floor Joist strength questions
- Thread starter DaveB
- Start date
I've repaired those and similar type truss fl jsts in the past. They are a lot stronger than they look but under longer spans they will sag over time.
If the building is not constructed and you have the option ask the builder to use a floor system with less deflection such as L/480 in the room you are interested not the entire level. It will add a bit to the construction cost but labor will remain the same.
Else have some extra squash blocks installed and box the beams with cdx ply in the area you are considering setting up your monster.
If the building is not constructed and you have the option ask the builder to use a floor system with less deflection such as L/480 in the room you are interested not the entire level. It will add a bit to the construction cost but labor will remain the same.
Else have some extra squash blocks installed and box the beams with cdx ply in the area you are considering setting up your monster.
The builder of the place I probably won't buy (the one with the laundry/utility room) reported back to the agent and said it's 18" open web rated at 65psf and it's over a 17' span, and that he'd be confident in any size tank against the wall. What he did not specify was how far apart they are on center. But at 16" that'd be 6 trusses for 96" and a load over 6600 psf by the numbers. So in theory a 300+ would work just fine. Heck, even at 24", if lined up precisely on 4, it should hold it.
In that case I start to wonder not about the truss, but the framing. That's my next question for him and/or my landlord (who has yet to get back to me about the spacing in his unit, which is our more likely purchase). Chicago homes are cinder block outer walls and just a wood frame inside them (and usually poorly insulated- this city is full of shoddy construction). Some of the framing I've seen is actually like a 2x2. I assume this can't possibly bear a load. I've never seen one of these buildings in progress though so I don't know what does - perhaps the load is borne by some kind of cutout ridge in the cinder blocks? I think, but am not positive, that this is how it is in our current garage, which had no problems holding about 250 gallons worth of kiddie pool 2 summers ago for my dogs to cool off in. I'll have to go out and check tomorrow.
If that's the case, I assume that I can trust the PSF calculations.
If that's not the case, I'd have a really hard time trusting anything. Also (and this is the first question where I truly feel like a moron) - does it make a difference what floor you're on? Does a wood frame's ability to bear a heavy load decrease as you get up several stories?
In my mind, that seems less stable. But if that was the case, skyscrapers wouldn't exist, so I know my mind is just being dumb.
My best bet is to have the landlord tell me exactly what wood it is and where he got it, so I can then ask the supplier for the full specs, then give that to a structural engineer. It looks like to get a permit for some roof deck additions (pergola, garden, other stone-based landscaping for my dogs to pee on with the appropriate drainage system set up - great inspiration here) I need an engineer to come anyway before I get a permit, so I might as well have him consult on a tank too. But I'll still pester you smart people about it in the meantime, because that at least lets my mind keep wandering and making plans for homes I don't even own yet. (Sure beats working!)
In that case I start to wonder not about the truss, but the framing. That's my next question for him and/or my landlord (who has yet to get back to me about the spacing in his unit, which is our more likely purchase). Chicago homes are cinder block outer walls and just a wood frame inside them (and usually poorly insulated- this city is full of shoddy construction). Some of the framing I've seen is actually like a 2x2. I assume this can't possibly bear a load. I've never seen one of these buildings in progress though so I don't know what does - perhaps the load is borne by some kind of cutout ridge in the cinder blocks? I think, but am not positive, that this is how it is in our current garage, which had no problems holding about 250 gallons worth of kiddie pool 2 summers ago for my dogs to cool off in. I'll have to go out and check tomorrow.
If that's the case, I assume that I can trust the PSF calculations.
If that's not the case, I'd have a really hard time trusting anything. Also (and this is the first question where I truly feel like a moron) - does it make a difference what floor you're on? Does a wood frame's ability to bear a heavy load decrease as you get up several stories?
In my mind, that seems less stable. But if that was the case, skyscrapers wouldn't exist, so I know my mind is just being dumb.
My best bet is to have the landlord tell me exactly what wood it is and where he got it, so I can then ask the supplier for the full specs, then give that to a structural engineer. It looks like to get a permit for some roof deck additions (pergola, garden, other stone-based landscaping for my dogs to pee on with the appropriate drainage system set up - great inspiration here) I need an engineer to come anyway before I get a permit, so I might as well have him consult on a tank too. But I'll still pester you smart people about it in the meantime, because that at least lets my mind keep wandering and making plans for homes I don't even own yet. (Sure beats working!)
I've read that. It dispells some old myths but doesn't really get us any closer to making a conservative determination of what a certain floor should hold. It also seems pretty outdated since it doesn't even address IGF, let alone trusses.
I'm still also not clear on what happens if a stairway runs up along the side load bearing wall. If it's open above and below, do those several joists just get their loads completely handled by the single joist on either end that do continue over to the load bearing wall? Do they sister them on either side there to account for the additional strength needed? This has nothing to do with tanks, I'm just curious.
I'm still also not clear on what happens if a stairway runs up along the side load bearing wall. If it's open above and below, do those several joists just get their loads completely handled by the single joist on either end that do continue over to the load bearing wall? Do they sister them on either side there to account for the additional strength needed? This has nothing to do with tanks, I'm just curious.
Around stairwells and openings they use trimmers. A header will pick up the shorter span jst's and transmit that load equally to the trimmers. Some times this is just a double jst and if the load is too great you might see engineered lumber such as a L.V.L. or such. A lot of times with stariwells it is just one trimmer and the other end of the hdr sits on a bearing wall or similar.
Remember the jst's that the hdr supports have their load split in half with only 1/2 their load on the hdr and the other half on their other end. Then the hdr's load is split in half between the two trimmers or it's bearing ends.
The floor diaphragm you described sounds more than able to support the tank but if you have an engineer on hand to peruse your plans that would be advisable.
Remember the jst's that the hdr supports have their load split in half with only 1/2 their load on the hdr and the other half on their other end. Then the hdr's load is split in half between the two trimmers or it's bearing ends.
The floor diaphragm you described sounds more than able to support the tank but if you have an engineer on hand to peruse your plans that would be advisable.
Update: We saw the #1 possible place again tonight. The back wall, opposite the fireplace, is the PERFECT place for a big display tank. 19 feet of uninterrupted wall space. So yeah, the biggest possible tank is going there... I'm thinking 120x30 footprint could work 
I need to talk to his supplier and then verify it with a structural engineer, but he said it's open web trusses and they're 16" on center for sure, rather than going wider because they're stronger. They sit right on the block, which bears the load of a 17'7" span.
It was larger this time than my memory told me it was, so I was really pleased with it, fish tank-wise. Here's a pic of the space (they're working on adding in the new raised panel wainscoting). The couch cluster would only take up about 10 feet tops from the fireplace, leaving room for a nice aisle and then massive tank... now we just need to make sure we're on the same page for the price.
I need to talk to his supplier and then verify it with a structural engineer, but he said it's open web trusses and they're 16" on center for sure, rather than going wider because they're stronger. They sit right on the block, which bears the load of a 17'7" span.
It was larger this time than my memory told me it was, so I was really pleased with it, fish tank-wise. Here's a pic of the space (they're working on adding in the new raised panel wainscoting). The couch cluster would only take up about 10 feet tops from the fireplace, leaving room for a nice aisle and then massive tank... now we just need to make sure we're on the same page for the price.
The design of your tank stand should also be considered for spreading the load over more aria. For example a stand with four or six small legs directly on the floor transfers the load to a much smaller space than larger and more legs transferring the load to two by fours then to plywood then to the floor.
Followup:
We bought, closed, and moved into the house. It's pretty awesome to own instead of rent. My other big project, besides fish, is distributed A/V, so I'm wiring the whole thing. Today I poked a giant hole in the top of the back bedroom closet so I could see between the floors. I'm pretty sure I could park a car on the upstairs floors. Here's a picture of what we've got in there...
14" high open web trusses made from double stacked 2x4, spaced 19" on center.
I'm not sure how much strength the dual 2x4 stack actually adds, since I'm not an engineer, but I get the sense that it's bulkier than it really needs to be. But I expected 2x2 construction, not 2x4, so that 19" on center instead of 16 seems perfectly reasonable.
Right? Wrong? How much weight will it hold at one end of an 18' span? What about a 14' span to the stairs (ie, not terminated at the load bearing wall)? There are two potential spots, depending on how we furnish things.
Tearing apart a new house is fun.
We bought, closed, and moved into the house. It's pretty awesome to own instead of rent. My other big project, besides fish, is distributed A/V, so I'm wiring the whole thing. Today I poked a giant hole in the top of the back bedroom closet so I could see between the floors. I'm pretty sure I could park a car on the upstairs floors. Here's a picture of what we've got in there...
14" high open web trusses made from double stacked 2x4, spaced 19" on center.
I'm not sure how much strength the dual 2x4 stack actually adds, since I'm not an engineer, but I get the sense that it's bulkier than it really needs to be. But I expected 2x2 construction, not 2x4, so that 19" on center instead of 16 seems perfectly reasonable.
Right? Wrong? How much weight will it hold at one end of an 18' span? What about a 14' span to the stairs (ie, not terminated at the load bearing wall)? There are two potential spots, depending on how we furnish things.
Tearing apart a new house is fun.
