How secure is a ledger fastened to concrete block?

jerseyguy1996 · 09-27-2009, 04:29 PM

Good Afternoon everyone,

I am brand new to this forum. I recently purchased an old house and I'm in the process of getting things set up. I know there will be plenty of projects to do on it (already we are removing wallpaper and painting) but I have one issue that needs fairly quick attention so I will begin my life on this forum with it.

The home is built on a crawl space. Most of the crawl space is accessible from the outside. However, a small addition (a mudroom) was added to the front of the house (not sure how long ago) and the crawl space under it is vented but the vent is not big enough to allow access into it. The only way to get in there that I can think of would be to go in through the top by ripping the floor out. I managed to snap a photo of the space through the vent and I can see that the joists are supported at the ends by what appears to be a 2X ledger, on it's side rather than on its end??? I would like to place a fairly heavy aquarium in that room and I am concerned about the weight of the water putting too much force on the ledger. The tank fully filled is probably about 700 lbs, plus the weight of any individual or individuals standing next to the tank. My concern is that since the 2X is on its side and it appears that the ends of the joists don't butt up fully with the concrete, that it could create a cantilever force that could rip the ledger out. Anyone have any thoughts on this possibility or some knowledge of how much weight those ledgers should be able to support?

Pictures of the crawl space are below.

Daniel Holzman · 09-27-2009, 04:46 PM

You have made a very astute observation. The ledger supporting the floor joists appears to be undersized, plus there is no way to tell from the photo how the ledger is attached to the concrete block. There are at least four possible failure modes for the structure, as follows:

1. The ledger bolts (if they are bolts) fail in shear. This would happen if the bolts are undersized.

2. The concrete blocks fails in shear from the vertical load on the bolts.

3. The ledger fails in bending due to the vertical load from the floor above.

4. The ledger fails in shear if the bolts are stronger than the ledger.

There are other possible failure modes, including buckling, which are more complex to analyze.

Regardless of whether you put an aquarium up there, you need to closely examine the connection detail between the joists and the ledger. You may be able to reinforce the connection using Simpson joist hangers on the sill. You may be able to attach a larger ledger to the block to replace the one that is there. You may be able to attach additional supporting elements (probably through bolts) to support the ledger.

The critical point is likely to be the strength of the connections between the various structural elements. Make sure you examine the method used to attach the ledger to the block very carefully.

**oh'mike** · 09-27-2009, 05:26 PM

From what I can see in your photo the floor joists appear to be sitting on a row of 1/2 blocks--measure the size of the blocks in your photo.

The 2x4 must be hiding a seam,I'll bet the 2x4 is there only to keep the joists aligned for the mason.

I hope I'm right.

Let us all know what you find out. If you and Daniel are right about that being a ledger--Well damn--- I can't imagine any one making a ledger that way. I bet they are on the block and your fish will be fine.--MIKE

jerseyguy1996 · 09-27-2009, 06:37 PM

Thank you Daniel and Mike for your observations. After reading Mike's comments I took a closer look at the photo at its original size. I need to try to take a shot at a different angle to confirm it but I think he may be right and they are sitting on a row of concrete blocks. If you are able to really zoom in on the connection between the joists and the concrete blocks it does appear that the lower 2X4 is resting on its side on a row of 1/2 blocks and the upper 2X4 is resting on its edge on the row of full blocks which I assume just gives something to nail the subfloor to. I hope that is the case. So the footing under the blocks would have to be wide enough to fit a row of full size blocks and a row of 1/2 size blocks.

**oh'mike** · 09-27-2009, 06:58 PM

That photo say's you're good. With a new place you'll find plenty of other things to worry about.

Glad that one turned out well.MIKE

KAdams4458 · 09-27-2009, 07:00 PM

I can't see the problem well enough to comment on the ledger, but I do have a couple of observations that have not yet been brought up.

1. I don't believe the wood in contact with the block is treated.

2. no vapor barrier.

Is this conditioned living space? I presume it is, if you're looking to put an aquarium in there. You might even find that insulating the floor would be nice. Of course, getting under there to do anything seems like it will be the tough part.

jerseyguy1996 · 09-27-2009, 07:12 PM

Oh yes....plenty to worry about Mike. My first two surprises have been good ones though. The first was when I peeled off the wallpaper in one of the bedrooms and found the original plaster walls in perfect condition. The second was the outcome of this thread. Of course going forward may not be so easy. I will never understand why anyone would feel it necessary to cover every square inch of a house with wallpaper or why they think that thin wood paneling is an appropriate substitute for plaster or drywall.

concretemasonry · 09-27-2009, 07:17 PM

I really do not see any floor joists supported by a ledger.

What I see is a 2x joist supported by a 2x sill that is sitting on a 4" (half high) solid concrete masonry unit and not attachment to any ledger.

The block below the 4" high unit may be either 8", 10" or 12" thick and the sill is at least 4" deep by 2" thick (nomiminally).

Dick

Is the 700# near the supporting wall and what is the floor area of the aquarium where people can not stand?

Dick

jerseyguy1996 · 09-27-2009, 07:19 PM

Good observations to make KAdams. I have thought about the vapor barrier situation. The house is built on piers rather than a solid wall foundation and at some point they built, I think they call it a skirt??? around the bottom to hide the opening. There is lots of ventilation. I can also say that having crawled around under the accessible side of the crawl space, the ground down there is absolutely bone dry. In fact I had to wear a mask because just my movement was causing the actual dirt (well more like sand) to blow around. I am not sure if that would be enough to not need a vapor barrier so I do plan to find out what it would take to put something down.

jerseyguy1996 · 09-27-2009, 07:38 PM

Thanks ConcreteMasonry for the reply. The attached picture is kind of a rough drawing of where I would like to put the tank.