Thread: Supporting joists from below

Hi folks!

More about me in the introduction thread. I'll get straight to the point here.

I am doing a first floor bathroom in a 1912 house. It is an ell so there is nothing above it. It sits over a crawl space with masonry walls and a concrete floor. The floor looks properly poured (not just thrown over dirt as I have found in a previous old house). The joists are southern yellow pine 2x10s and one 2x8 (actual measurements), 16" OC and span 5'8", total of 4 in the work area.

Two of the 2x10 joists were significantly notched (10x6") at one end by an HVAC guy with a Sawzall. To be fair it really was the ONLY thing he could do at the time and I get that. He reinforced the joists with 2x4s glued and screwed and run all the way to the joist pocket on the notched end.

My reno plan includes marble tile. My deflection factor falls into spec. However, I could not account for the notching when I calculated it out. The floor absolutely does not move even when jumping on the affected area. I will be installing 3/4" plywood with the grain perpendicular to the joist with another layer of 1/2" ply on top. I would like to add some support under the floor with special attention to the two notched joists. My plan is to build a proper bearing wall with studs located under the joists all the way across the crawl space (span is 6' 8"). I can double the top plate if necessary but do not think it is required. I will cross brace the joists as well. It will not be dry-walled but left open to allow access to the area. The live load will be somewhat significant with the marble floor and a new shower (solid surface base not a mud bed) but the tile will actually be situated over the un-notched joists in an area that is only app 3.5" wide.

I want to make sure that this is an acceptable solution for my situation but I cannot get my city's building inspector to come out and tell me how they want me to fix the problem. I was told "we don't do that". It's not that I need them to tell me how to do it but how THEY want me to do it as it can be done in several ways that I am aware of. I cannot find this addressed in any code listed on-line. I'm very much aware that the notches are not to code but tearing out the ductwork, rerouting it and replacing the joists is not possible.

So my question is, is this a prudent, safe and accurate remedy to add support to this floor and should I reasonably expect it to pass muster?

Thanks in advance.
Lynne

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Anybody?

Originally Posted by Lynne Allison

Anybody?

I didn't see this before, but ...

Originally Posted by Lynne Allison

It sits over a crawl space with masonry walls and a concrete floor. The floor looks properly poured (not just thrown over dirt as I have found in a previous old house). The joists are southern yellow pine 2x10s and one 2x8 (actual measurements), 16" OC and span 5'8", total of 4 in the work area.

You have me confused.


You say the floor is "a concrete floor", then you say the "joists are ... " and a concrete floor should not be supported by wood.


Is the floor a concrete floor, or is the floor a wood floor system with a full mud set floor for the floor tiles, which likely would also have been the wall behind the tiles in the bathroom in 1912 ... a full mud set wall system, likely even on metal lath for the walls.

Originally Posted by Jerry Peck

I didn't see this before, but ...
You say the floor is "a concrete floor", then you say the "joists are ... " and a concrete floor should not be supported by wood.
Is the floor a concrete floor, or is the floor a wood floor system with a full mud set floor for the floor tiles, which likely would also have been the wall behind the tiles in the bathroom in 1912 ... a full mud set wall system, likely even on metal lath for the walls.

Sorry for the confusion. No, it's a normal wood floor in a first floor bathroom. Joists supported on masonry foundation walls in the usual fashion with a wooden subfloor. This bathroom was an un-permitted renovation done in the 50's of a large pantry type closet that sits in a bump out on the back of my house. There is a large crawlspace underneath the bathroom which gives me good access to the joists above. I have a full basement with access to this crawlspace which is actually about 3-3 1/2 feet above the basement floor because it's under the bump-out. The floor of the crawlspace is poured concrete rather than gravel or dirt. The bathroom floor is, or I should say was, 1x8 subfloor on the diagonal with a very narrow strip hardwood floor on top. If this still doesn't make sense I'll take a picture when I get home tonight and post it. Thank you for responding. Hopefully I'll get somewhere with this.

Without photos r a drawing it is hard to give a meaningful answer. Why can't the ductwork be placed below the joists?

Originally Posted by Mark Reinmiller

Why can't the ductwork be placed below the joists?

That's what I am wondering too, especially with 3-1/2 feet underneath.

Originally Posted by Jerry Peck

That's what I am wondering too, especially with 3-1/2 feet underneath.

Thanks for the reply. Because of the construction of the house and where we have to tie in there would be too many 90 degree turns in the duct. I have tried that route but the HVAC guys have said no bueno. All of them! So I'm back to my original question. I appreciate the thought you all are putting into this.

Generally speaking (without seeing details) I do not have a problem providing support for floor joists by using a stud wall bearing on a floor slab. The loads are small and as long as there are no large voids below the slab and there is not much potential for heaving of the slab this can work just fine.

Originally Posted by Mark Reinmiller

Generally speaking (without seeing details) I do not have a problem providing support for floor joists by using a stud wall bearing on a floor slab. The loads are small and as long as there are no large voids below the slab and there is not much potential for heaving of the slab this can work just fine.

Thank you so much Mark. It's good to know that I'm heading in the right direction. The inspectors in my town can be somewhat difficult to deal with even when I, as a homeowner, am trying to do the right thing. Most people refuse to deal with them and don't pull permits at all. That's not how I roll. I respect the job you guys do and want to do things the right way.

If I get a chance later tonight I will throw some pictures up so you can see. I'm not terribly concerned that I'm going to have huge issues as the span is not even 6 feet and the joists are enormous but I come from a family of overbuilders and always take the conservative approach. Also, I'm not cheaping out on the materials I'm using and I'd rather not, and probably couldn't, have to pay for a redo because I failed to put some forethought into this project.

Your input is much appreciated.

- - - Updated - - -

You really don't want to change the type of foundation support.
I have no idea what type of soil or foundation you have, but in general a basement or crawl space slab will behave differently than a full footing foundation or piered foundation. Simple slabs are designed to float on the soil while the supporting foundation is dug deeper into undisturbed soil or rock at a deeper, and therefore more stable, zone.
Heaving is not the only concern, especially if you have clay soils and different seasonal moisture levels.
I see this quite often in my area with older crawl space foundations and it never works adequately and sometimes literally tears the house apart with differential movement. I would encourage an alternate solution that transfers the load to the existing foundation and/or consult a structural engineer familiar with the soils in your area.

Originally Posted by Jim Luttrall

You really don't want to change the type of foundation support.
I have no idea what type of soil or foundation you have, but in general a basement or crawl space slab will behave differently than a full footing foundation or piered foundation. Simple slabs are designed to float on the soil while the supporting foundation is dug deeper into undisturbed soil or rock at a deeper, and therefore more stable, zone.
Heaving is not the only concern, especially if you have clay soils and different seasonal moisture levels.
I see this quite often in my area with older crawl space foundations and it never works adequately and sometimes literally tears the house apart with differential movement. I would encourage an alternate solution that transfers the load to the existing foundation and/or consult a structural engineer familiar with the soils in your area.

The problem with answering general questions when people live in different areas is that things do vary significantly from one area to another. Being in TX maybe you deal with shrink/swell clays. In my area and in Ohio that is not the case. We have a lot of clay, but it is generally pretty stable. Assuming a crawl space slab is not sitting on very wet clay this practice works quite well in my area.

Originally Posted by Mark Reinmiller

The problem with answering general questions when people live in different areas is that things do vary significantly from one area to another. Being in TX maybe you deal with shrink/swell clays. In my area and in Ohio that is not the case. We have a lot of clay, but it is generally pretty stable. Assuming a crawl space slab is not sitting on very wet clay this practice works quite well in my area.

Thank you both for your input. I clearly have much to learn and further investigating to do. As it stands since the local building inspectors who know of such things as soil stability in my area are unwilling to indicate how they would like me to handle the situation I'm pretty much going to be forced to try Plan A and see if it passes muster then go on to Plan B if it doesn't. Or C. Or D.

Originally Posted by Lynne Allison

Thank you both for your input. I clearly have much to learn and further investigating to do. As it stands since the local building inspectors who know of such things as soil stability in my area are unwilling to indicate how they would like me to handle the situation I'm pretty much going to be forced to try Plan A and see if it passes muster then go on to Plan B if it doesn't. Or C. Or D.

Investing in the advice of a professional prior to beginning the job won't be wasted money.
The advice of a structural engineer or other professionally make your job cheaper in the long run.

Originally Posted by Jim Luttrall

Investing in the advice of a professional prior to beginning the job won't be wasted money.
The advice of a structural engineer or other professionally make your job cheaper in the long run.

I completely agree. I have done this in the past. Unfortunately the local BIs did not agree with the structural engineer. Long story.

With that small of an area, and with 3-3 1/2 feet working space, why not bolt ledgers to the existing block walls, installed a girder from ledger to ledger, then vertically support the joists from the girder - that way everything is attached together and any movement will be consistent with each other, no differential movement of the slab or ground.

Granted, you may need to knock a few holes in the block and fill the vertical cells with concrete so you can bolt the ledgers to the block walls, but that seems easy enough to do and the comparative reduction in work an supporting the supports from the same structure eliminates other potential issues.

Originally Posted by Lynne Allison

I completely agree. I have done this in the past. Unfortunately the local BIs did not agree with the structural engineer. Long story.

Lynne, I would like to make sure you understand this is a forum for "home inspectors," not for "building inspectors." The two fields are very different.

I have never met a competent building inspector who would weigh-in on how a particular assembly should be constructed. That would be a professional conflict of interest for a building inspector.

Perhaps you already have realized the nature of this site. I hope your project proceeds nicely for you.

Originally Posted by Jerry Peck

With that small of an area, and with 3-3 1/2 feet working space, why not bolt ledgers to the existing block walls, installed a girder from ledger to ledger, then vertically support the joists from the girder - that way everything is attached together and any movement will be consistent with each other, no differential movement of the slab or ground.

Granted, you may need to knock a few holes in the block and fill the vertical cells with concrete so you can bolt the ledgers to the block walls, but that seems easy enough to do and the comparative reduction in work an supporting the supports from the same structure eliminates other potential issues.

That is an excellent idea that never occurred to me! It shouldn't be difficult to do. Dirty but not difficult.

Originally Posted by Grant Medich

Lynne, I would like to make sure you understand this is a forum for "home inspectors," not for "building inspectors." The two fields are very different.

I have never met a competent building inspector who would weigh-in on how a particular assembly should be constructed. That would be a professional conflict of interest for a building inspector.

Perhaps you already have realized the nature of this site. I hope your project proceeds nicely for you.

My apologies. I think I did equate one with the other. Although wouldn't the knowledge base of the two distinct entities somewhat parallel each other? At any rate. I didn't want the BI to tell me HOW to do it as there are several ways I could accomplish this. What I needed from them is how they WANTED me to do it to meet my city's code as I have been unable to find anything anywhere that addresses this particular situation. Frankly, I didn't want to put the time an money into simply guessing what would satisfy them only to have them tell me it was inadequate and I should have done it some other way.

Thank you for pointing out my mistake. Again, please accept my apologies for the confusion. I appreciate everyone's efforts to assist me.

No apologies are necessary, of course. The thread is titled "Questions from Home Owners, Home Buyers and DIY" to encourage this kind of supportive discussion. It keeps us mindful (and our minds sharpened) by engaging in such discussions.

I just did not want you to have the impression that you were discussing the matter with building inspectors. One of the main tenets of professional home inspectors are that we are not "code" inspectors. This simply means that the ever-evolving world of building codes do not form our own industry's guidelines.

Building inspectors, on the other hand, are simply code enforcers. Once they approve a project's progress, they will likely never visit it again. Although "quality" is a code requirement under the form of "workmanship," they are simply not in the position to favor one code-compliant assembly over another. You are not alone in wishing they sometimes would do exactly that.