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Unread 11-17-2020, 05:04 PM   #1
omarcathy
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Having the same problem! Contractor cannot find a concrete block peir to use

Hello! I am replying to this nearly 10 year old thread as this is the only thing online I can find that relates to our problem. We have the exact same issue as the original poster - our hardwood floors are extra shaky when someone walks around our new granite island making it uncomfortable to enjoy being at the island clearly it should have been mentioned pre reno and our contractor neglected to address this, but now that we are done all we can do is try to add support underneath. Same problems as original poster - our basement is unfinished, but we have plumbing, electric, and hvac in the way preventing sistering of the insufficient 2X10X16 joists (our house was built in 1972 when codes were different ). We don't want to build a wall as that would cut a large usable space in half and look like a jail wall mid-basement, so our kitchen contractor has suggested using an LVL beam (it'd be about 12.5-13 feet long) supported by posts perpendicular to our joists and the island, right in the middle of the span and the island to 85-90% correct the extra shaking.

We have permanent jacks installed already supporting the load bearing walls at each side of the kitchen, each of those jacks are on plates resting on 2x2x2 of rocks buried beneath the concrete nearby where we would put those posts supporting the LVL, so we don't want to break up to concrete slab floor and dig out and make new footers for these posts as it would disturb those footers. So, we are trying to figure out what kind of concrete block pier to use on top of the concrete slab to distribute the weight of the LVL instead - our contractor says he can't find one and says since it's not load bearing, we don't need footers, we could just attach the posts with simpson brackets right to the concrete slab floor. Seems best to just use a footer since the concrete is only 4-6 inches thick, we don't want to take chances. Plus we have an old crack in the slab nearby from previous hydrostatic pressure (that has since been relieved by install of partial drain system and sump pump.) Can anyone help us with a suggestion, perhaps share a link of what could be bought for this so we can share it with our contractor? Any help would be very much appreciated!!

(Apologies if I am posting incorrectly - I am not sure how to "bump" threads as that might have been the right this to do here... again thanks in advance for any help!)
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Unread 11-17-2020, 06:56 PM   #2
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Welcome, Cathy.

I've separated your post form the other visitor's thread to avoid confusion in both places. We find the second visitor's situation is never really "the exact same issue" as the first visitor's. A moderator can give it a more generic title any time you'd like to suggest one.

Do you plan to tile the floor around this island?

I'm afraid we don't have enough information to allow what would be an engineering decision on what might be required to properly support your new beam. And I'm afraid I'm a bit confused by your description of your other support post design:
Quote:
Originally Posted by Cathy
...each of those jacks are on plates resting on 2x2x2 of rocks buried beneath the concrete...
If your current contractor is sufficiently knowledgeable to have sized your new support beam, I'm quite surprised that he would also say:
Quote:
Originally Posted by Cathy
...and says since it's not load bearing, we don't need footers.
Sounds like a load bearing situation to me.

Without knowing the design of your below grade slab I can't really suggest what you might need to set your support posts on. My first inclination would be to tell you to cut holes in the concrete and dig to a suitable depth for your location and pour some footers. Also, with my confusion about your existing support post situation, I can't address your concern with cutting such holes.

My opinion; worth price charged.
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Unread 11-18-2020, 12:29 PM   #3
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Need to bolster flooring from below, heavy granite causing shaking

Thanks for your reply cx! Sorry for confusion. Hopefully I can re-explain clearly this time, sorry in advance for the long description:

Per our contractor, the LVL and posts would only being used only to lessen the deflection of the flooring which our contractor says is what is causing the shaking when someone walks by the island due to the heavy load of the granite on the somewhat insufficient joists + thinner than average subfloors. We didn't have this problem in the kitchen before reno because there were several layers of subfloor and laminate sheet flooring piled up, which made the floor firmer, plus the table in the center was no where near as heavy as the granite + island cabs that is there now. With all the layers of old flooring removed now we have issues. We don't have tile floors - we wanted them but worried they'd be too heavy - but have hardwoods, and the subfloor is only 5/8 thickness instead of 3/4. We didn't replace subfloor for thicker since our plan was to feather the new hardwoods into the old hardwoods in the adjoining room, at the time we didn't realize we'd have this issue and now we are stuck with shaking. We did notice the subfloor felt "floaty" before hardwoods were installed and worried then it should be replaced but contractor sales rep insisted it'd be fine once 3/4 inch hardwoods were added and never mentioned this would occur. Side note - that sales rep was suddenly "no longer with the company" midway through our job, we can only guess due to this type of oversight - but here we are.

We already tried blocking, that didn't help. Per our contractor, given the electric, plumbing and HVAC in the way that makes sistering the joists a more complicated and costly option, our other options are to build a wall under the island or if we don't want to block off that whole area of the basement to use posts and an LVL. It's a 13.5 foot span from one load bearing wall to the other, we'd go from one load bearing wall to about 1 foot short of the other load bearing wall (to avoid plumbing). The reason our contractor says to use an LVL/wall across most of the span vs just under the island is because if we use a shorter LVL/wall the deflection would just transfer to several feet away where there is not support underneath.

The permanent jacks I mentioned are already in place and are supporting the load bearing walls on either side of our kitchen - on one side they are at 5.5 feet and 11 feet along the 16 foot span, on the other at 5.5 ft, 7 ft and 11 ft and were used to lift old joists that were insufficient for the load/stupidly cut for plumbing and sagging, and are now permanently bolstering those load bearing joists. They are essentially lally columns that each sit on larger plates below the concrete slab floor but on top of a large 2ish foot wide/2ish foot deep bed of filler rocks with concrete poured over it all to lock it in and even out with concrete slab floor.

The posts supporting the LVL would go between them at about 8 ft since this is the middle of the joists and the middle of the island/granite area. We can't dig out footers for the the posts for this new LVL because it would come too close to disturbing the footers for the load bearing permanent jacks - our contractor says we don't need to do footers though since the LVL will not really be load bearing, it's just helping to manage deflection of the floors. We thought since it's helping manage the load of the granite that footers would be good, but does what our contractor say sound right? And if not, what do we suggest he use as a footer on top of the concrete slab since we don't want to dig?

"Engineer Bob" had suggested concrete block piers in the previous post I originally replied to, which is why we are asking about this. OUR contractor says he cant find something to use but that we don't need them.

Need help figuring this out, hoping someone could give advice here.
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Unread 11-18-2020, 01:47 PM   #4
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If I'm reading this right, the supports for the LVL would bear on the slab? There is no provision for half measures in load calculations. It's load bearing or it's not. This certainly sounds like it will be.

If I were doing this I'd want to see that support post point load spread over as large an area as possible, but that's absolutely from the seat-of-my-pants and I'm not there to assess probability of success.

What's being proposed might go some distance to mitigate bounce, but I doubt you'd get an engineer to sign off on it. I guess my question to your contractor would be, "what if it doesn't work? Who will pay, and what would the next step mitigation be?"
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Unread 11-18-2020, 02:02 PM   #5
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you could also add in a partition wall in the basement below the room to add support. This spreads the load as much as possible. Not exactly structural per-se, but works for your purpose. Cut the vertical studs so they have to be tapped in with a mallet. Glue/nail a bottom plate and top plate. Do it in 2x6 for added support. No doubt, this would eliminate allot of the deflection. I did it in my house. When finishing the basement the added walls really stiffened up the first floor. Most builders will pre-build the interior walls and just shim them into place. This doesn't help much if at all. Build them in-place and cut each stud to fit.
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Unread 11-18-2020, 02:19 PM   #6
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To me it isn't load bearing, in the sense that it won't be supporting loads from the roof or a second story, but it will have to support the weight of the island. Semantics, I suppose, but I think that's what your contractor is saying.

And if it only needs to support the load from the island, I wonder if you couldn't just build a support under only the joists the island is sitting on. This would be easy, quick, and inexpensive to test. Buy however many 2X4's as there are joists, cut them juuuust long enough so they need to be hammered into place between the bottom of each joist and the concrete floor yet still be very close to plumb.

Then go walk around the island and kitchen as normal, see if the bounce is eliminated, or reduced to an acceptable level. If it is then acceptable you'd need only to support those joists with a more permanent solution, and perhaps a short wall would work.
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Unread 11-18-2020, 03:54 PM   #7
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Well, Dan, we'll have agree to disagree. Floor loads don't get a pass just because they're not holding up a roof or second story but I get your thinking.

I'd be willing to bet if one were to pull a tight string across the bottoms of joists there would be obvious sag. Getting that straightened out first would be my priority in addressing bounce.

I'm interpreting from original post that a wall would be less desirable or perhaps not possible, but agree a "test wall" might make for a quick for "floor feel" assessment.

As a side note and not really applicable in this case methinks: Sometimes I-joists at design span have more bounce than I'd like, but they do pass muster from an engineering standpoint. Heavy cabinetry and especially countertops exacerbate the issue. One of the few cases where I'd consider "more is better" a reasonable philosophy to adopt.
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Unread 11-18-2020, 04:20 PM   #8
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Gotta side with Peter on the load bearing aspect, Dan. If we're supporting part of the structural load of the building, we're making load bearing supports.

I also agree about the likelihood of some sag, perhaps even a good deal of sag, in the existing joists. Without some photos and perhaps a good drawing with dimensions it's tough to tell how much this floor really needs. And for me to get a picture in my pea brain about the relative locations of all the existing supports and the target area.

Paying a few hundred bucks for a local structural engineer to evaluate the situation might be dinero well spent. I've found that if you just need an evaluation and not a certification they can be pretty reasonable in their charges.

My opinion; worth price charged.
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Unread 11-18-2020, 05:06 PM   #9
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Probably has much to do with my relative inexperience, Peter. When I hear "load bearing" I immediately think structural walls, foundations, etc.

Like you, I'm certain the assembly is sagging a bit under the weight of the island. I'm just not convinced that, in this case, structural footers are necessary unless maybe if that island is a couple thousand pounds.

The joists are taking all the building structural loads at each end and at the rim/bands, and absorbing dynamic loads within the free span. So, at most, the new mid span support, in whatever form that takes, only needs to support the island.

If a short length wall could be built to support only the joists upon which the island is resting and solve the bouncy floor problem I'd be pretty comfortable with spreading that load along a 2X bottom plate on the concrete floor. If a short wall is out of the question and a much much longer beam must be installed with posts, the point loads are much greater.

In any case, it would be best to either remove the weight, or jack up the sagging joists, when implementing whatever fix is determined most suitable.
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Unread 11-20-2020, 11:36 AM   #10
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Having the same problem! Contractor cannot find a concrete block peir to use

Really appreciate everyone's thoughts! We'll have to fiddle with string this weekend and see if any sagging, but eyeballing it, there doesn't appear to be much if any sagging under the island - the reno was only finished in March so maybe not enough time for that yet. Definitely want to avoid that!!

Actually the joists closer to the edges/load bearing joist are lower, since the load bearing joists were sagging so badly for years they are still on the lower side compared to the center. That sag is barely noticeable now that we jacked up the load bearing joists when walking upstairs but if we did use an LVL, our contractor said he'd have to use shims on top of the LVL for some of those joists - including the ones the island sits on since they are in the center and higher from the floor than some of those towards the load bearing wall. Re: the comment about a prebuilt wall being shimmed in not being effective, that makes us wonder - is that a bad plan too?

Our contractor said he could just build a short partition wall right under the island, but then if that doesn't fix it/shaking just transfers to another spot we'd have to pay him again to come back out to lengthen it if needed. But our fridge is heavy too and our floors are old so too thin so we figured lets just sturdy up the whole length using an LVL and posts since the thought of the partition wall cutting up the large basement space wasn't ideal. Basically with our floors you can feel folks walking by you and it's not a big deal, but this island has made that walking feel like an elephant is walking nearby.

For spreading the load as far as possible on top of the concrete slab, what could we use that wouldn't look crazy to an inspector? This is where our contractor doesn't have an answer and we are not sure what to tell him. He's proposed using "Simpson ABA ZMAX Galvanized Adjustable Standoff Post Base for 4x4 Nominal Lumber" to secure the posts to the slab. Is a 2X bottom plate much different from this, could that be used for the LVL/post situation across the whole 13-sh foot span?

We don't know how long we'll be here so really don't want to do anything that raises eyebrows. We already hired and engineer to help asses the situation with the sagging load bearing joists, that cost us $700 just for a simple report with lots of info he said he would include missing. It was like pulling teeth to get more out of him, took over a month and maybe 20 emails. Though only 15 road miles from major cities, technicalyl we live in a rural area and because of this we have can't get anyone else out here for less than close to $1k. Building this wall/post and LVL would cost less than an engineer so we want to avoid that.

If it helps assess the load, the granite slab on the island is 38.5x58.5 and 1.25 thick if that helps...island cabs it sits on are 25 x 45, the granite overhangs 1 ft on two sides and 1.5 inch on the other sides. The granite can't possibly be a few thousand pounds because a couple of guys were capable of carrying it into the house.

We might be stuck with a full partition wall in the end if we can't figure out this load situation, might just add framing for a doorway so it could be small room or huge closet eventually...don't think jack studs for a doorway would need load distribution, right? Or would they too?

Again thank you all very much!!
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Unread 11-20-2020, 12:54 PM   #11
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Cathy, I fear we're still mixing some terms/descriptions here. First, all of your floor joists are load bearing. It might help a good deal here if you'd tell us exactly what you have for floor joists. Material (I'm assuming sawn dimension lumber), species, height, width, unsupported span, etc. Would give a better starting point in assessing the problem.

The LVL beam, if properly sized and supported, is a very good option to correct an overspanned joist problem. What to sit the supports upon is difficult to assess without being on site. And if you had a structural engineer evaluate the situation that is certainly one of the things that should have been specified. If spreading the load at the bottom of the support posts is all that's needed, something as simple as some 16"x16"x4" concrete blocks from your home center might be sufficient, but I can't tell that from over here. We would normally prefer to have the supports set upon a footer that is much the same as the rest of your foundation, but it might not be necessary in this application.

As for not doing anything that might "raise eyebrows," I think the presence of multiple lally columns will already have done that. But that's an indication of a problem corrected, which is far better than a problem existing such as you have now.

Nothing at all wrong with a little shimming under some of the joists when that support beam is installed. I would prefer, were I doing the work, to raise each individual joist into a flat, or nearly flat, plane before the final raising of the beam and setting of the end supports, but some shimming to make any final correction is not out of order so long as it's done correctly.

That island with its granite top in total can't weigh more than about 400 pounds, which is equivalent to two medium-large persons standing in the center of the room. While it's obviously causing you to feel its presence, it's not enough to upset the whole structure of your house. What useful information did the evaluating engineer give you, by the way, for your 700 dollars?

Again, some photos of your basement situation might be helpful.

My opinion; worth price charged.
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Unread 11-20-2020, 01:29 PM   #12
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Blocking between the joists helps to spread the load, but it does not actually increase the distributed load strength...it helps share the load with adjacent supports, but if they all are overloaded, they're still overloaded. It does change the resonant frequency of the floor's vibrations, which can help it appear to be stronger. Subflooring slightly improves the overall floor deflection rating, but only when fastened properly to the joists (generally, construction adhesive on the joist tops and proper fasteners). Subflooring is primarily providing strength between the joists (and to keep you from falling through!), not along the joists, as when installed, the primary strength axis is across them, not along them. More and thicker subflooring does add to the dead weight of the floor, leaving less margin for the overall strength for live loads (people, moveable items).

I wonder whether a steel plate with a lally column welded to it would spread the load enough to preserve the slab. Depending on the mix, concrete slab could have somewhere between 2500-5000psi compression strength (you'd not normally get on the high end for a residential install). Spreading the load out with a bigger plate than they normally have, say a 12" square versus a maybe 4x4 one that is more common would cut the load by a factor of 9, and going to a 15" square by 14.
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