New House sagging floors 1

[tonydutt]

First time poster...
I am a mechanical PE, but, need some structural advice for my house...

4 year old, 2-story house with a crawl space in eastern VA. Crawl is dry, tested girders and joists for moisture, no issues.

House is supported with concrete block piers. Girders are 6x6 treated lumber (not sure exactly which type of pine) and joists are 2X12 regular untreated pine.

My issue is on the first floor tile is cracking, wood floors are wavy, and drywall on a load bearing wall has cracked. second floor has several areas (above the load bearing wall from 1st floor) where drywall is cracking.

From my inspection of the crawl (random sample of 3 areas) the joists which are above the pier are high and the joists not above a pier are low (not all). So, I put a level on the girders in between the piers (on the bottom obviously) - totally level.

So, what I think I need is to do is to support the joists somehow. I have found a bunch of solutions including jack systems - which seem easy to install given the correct footing. But, then I read some posts here which discuss metal straps and whole bunch of other ideas, including sistering joists.
I could use some thoughts and ideas on possible solutions, possible downfalls, and things to avoid so I don't get taken when I get an estimate later this week.
I want to be econmical, too. The jacking system seems to be the best, but, probably the most expensive.

All the best, Tony

 

[cntw1953]

"From my inspection of the crawl (random sample of 3 areas) the joists which are above the pier are high and the joists not above a pier are low (not all). So, I put a level on the girders in between the piers (on the bottom obviously) - totally level."

Shouldn't wood flooring has slope of somewhat?
Are you positive there is no settlement of the piers?

 

[Stillerz]

If it turns out that the 6x6's are the problem you could temporarily support the floor joists and remove the 6x6's. Them on your block piers, remove the top course of block
and repalce it with a 4" termite block and then install double 2x10 or 2x12 girders.

 

[dhengr]

Tony:
Don’t be so resistant to good advice, that’s what you asked for, and there is a bunch of it in the various posts, if you know which nuggets to pick out. A structural engineer!, not a civil engineer or designer/builder. It looks like the latter caused your problems. Most of us have trouble with the IRC, so quit reading so hard or worrying about which edition you have; span tables alone don’t address your problems, and your “there are a lot of piers” should include, ‘but apparently not located properly,’ again not tabulated in the IRC. In your first post: “joists which are above the pier are high and the joists not above a pier are low...”; in your second post #2. “I don’t see any unsupported lengths of girder or joists.” In my lingo the girder is unsupported btwn. the piers and the center line girder is almost certainly under sized for its spans and loading or the piers must be placed closer together and under heavy jamb loads, etc. See my first post, as I take my tongue out of my cheek. The 6x6 is deflecting and thus your first statement. Do the string thing or get a laser level down there. 6' is a long span for that 6x6 girder with some of what I think is going on there.

Economical methods of repair, as you requested, are immaterial until you understand the real problems and what’s causing them. You really do need a experienced structural engineer to look at your problems, he/she will be able to assess the important details. You’re not having similar problems at the exterior walls, are you? You seem resistant to giving enough or the right kind of info. needed to further the discussion here. A sketch of the whole girder line (the problem area) would have been most helpful, along with the actual jst. spans onto the girder. What’s the total length of the girder line (the house), what are each of the span lengths, c/c of piers and end walls, show simple/continuous girder conditions over each pier? We just can’t see the important details from here. The photo of the conc. blk. pier is nice, that’s about what they usually look like. Is the girder bearing on the gross area of the pier or is it bearing on the end cross shell? Do the string thing, does it appear that any of the piers have settled, what are the relative deflections of the girders? How do simple supports (your photo) vs. continuity over supports relate to deltas and cracking? How do these spans and max. deltas relate to jamb loads above, to cracking, etc.? There’s about 500 #/ft. of DL on these 6x6 girders, which, I doubt, are graded or intended to be used as significant bending members, look for a grade stamp and/or treating label. That DL a long term loading and doesn’t include concentrated DL’s or LL’s (another 800#/ft.).

RE: SWComps question 2), no, but it’s not my house either. On the exterior, it’s pretty likely that the roof, wall and fl. loads are being carried by the brk. veneer, through the rim jst. and spanning jsts., if the brk. veneer was brought up tight under them, since the 6x6 sill beam will likely have shrunk across the grain. Maybe the brick veneer was not brought up tight under the rim jst. then there might be bearing issues on the sill beam. How is the brk. veneer tied to the conc. blk.? There aren’t indications of openings and/or piers in the ext. found. wall, and those would be important structural considerations. Trainguy, I meant no harm, except to point out that these kinds of rules of thumb are potentially dangerous in the hands of Tony’s builder or someone who doesn’t even understand the loads or causes of the problems. Read my original post again, and email me some other rules, this time on railcars , we’ll start our own forum. Stillerz’s 6JAN 11:55 fix is a likely fix once someone really assesses and understands the problems and causes. Csd72's 6JAN 3:52 post should be enlarged and pasted to the front of your file on this matter, make it your mantra until this is fixed.

 

[vandede427]

You're right, 20 psf would have been better. For residential, I use 10 psf for carpet and 20 psf for tile/stone.

The spans don't seem long enough to even develop enough deflection to crack.

The axial cracking (or splitting) can be typical of a post member, but that won't affect its strength too much. I don't buy into the moisture argument since you've said the crawl space is dry.

I would suggest that it's an issue with expansion/contraction due to temperature, not moisture.

 

[cntw1953]

Tony:

It will bring more understanding if you can expand your sketch to include at least an interior pier and pointing out the defective bearing wall. The interior joist support beam (you call girder) could be the source of problems.

 

[BAretired]

Without more information, we can only guess what the problem could be. Probably best to retain a structural engineer to look at the problem and recommend corrective measures.

BA

 

[Stillerz]

I do have to interject something here.
There is a lot of talk on this forum about "you need an engineer not a builder...". I can understand where it comes from as this is an Engineering Tips website.
However, you cannot discount the advice of a good builder in a situation like this. Keep in mind that very good structures were built for thousands of years and remain standing ...even well before Timoshenko was born.

I doesnt seem like your house is facing an impending collapse or that the foundations are giving way. While I cannot say this for certain, your problem simply seems like shoddy construction that could have been avoided if you had a builder that knew his ass from a hole in the ground.
I have built 50-60 house which were entirely custom and many more that were not. By "built" I mean I actually drove some nails and even laid out and cut some rafters.
I am no longer employed (or self-employed as a builder)as I am a full-time structural engineer.
Having said this, it seems like this type of experience has eluded mnay on this site, no offense.
A good builder might be able to fix your problem "to code" and be out the door with the home fixed for less than reataining a structural engineer to look at it.
Blasphemy you say!!!!!

 

[Stillerz]

...let the ribbing begin.
I can already think of a few specific guys on here that are going to rip my ass for that last post.

 

[cntw1953]

stillerz:

While history glorify builder's accomplishment, it does not keep record of failures. That is the reason we continusly to educate ourself since ancient time. As the knowlege base grows bigger and bigger, the smart fews (builders) have gradually lost their's edges to those equipped with better tools (engineers).

Hope this makes sense. Wish you, and believe you will, do well at school.

 

[Stillerz]

School?
I have been out of school for years and years.
The knowledge one can gain with his hands can equal that of his mind. Don't kid yourself.

 

[cntw1953]

Sorry, I mis-read full time engineer as full time student. Do not mean disrespect.

 

[Stillerz]

Nor did I.
Just offering another view...dissenting, apparently.

 

[tonydutt]

Thanks everyone for the great data and info. I really don't think I was resistant to any advice before, but apologies to any who may have thought so.
Recently, I have spoken to one of the structural engineering firms in the area. They probably have 40 or so engineers on staff - not sure how many have sat for the PE, but, I spoke to the owner who is a fellow PE. He told me to not hire his firm, because my isse could probably be fixed by a builder type who would do the same exact thing he would propose for $4-6k.
I had one of those builder types come out with 20 years in the foundation biz. He and I went under the house and measured everything. What we couldn't find were any girders that were not level, using a laser level.
We did find joists that we low on the spans of about 7-9 feet. He wanteed $20k (which includes his engineer's fees) to put up new piers and girders and level everything, including the old girders.

Subsequently, I ran my own little experiment with a single house jack for $30 from Lowe's. I was able to begin to level out one small area of wood floor (the worst of the whole house) by lifting one joist 1/8". I am not going to move it anymore as that was just a test. Nonetheless, it was fun doing it.

Thanks again. I travel a lot ion my job and will be gone for the next 3 weeks. I will certainly follow the thread as best I can and respond. I will try to get the full drawing scanned in before I fly out Sunday morning.

Tony
I am not ready to fork over $20k

 

[msquared48]

Another thought here.

2X12's can vary in depth from joist to joist by as much a 1/4 to 1/2" according to local framers I have talked to in the past. If joist hangers were used, or the joists rest on top of the 6X6's, this will call a waviness in the floor.

If 3/4" plywood was used for the flooring, plus screws and glue, much of this could have been mitigated. But the floor disaphragm was probably nailed, maybe glued, allowing the nails to loosen with time - any squeeks?

If hangers were used, shimming the seat of the hangers to get a constant depth could help. Similarly shimming the underside of the joists over the 6X6's could help too, if possible.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[hokie66]

I think Mike may be onto something. If the problems are not caused by deflection or cross grain shrinkage, then the original size of the members, and the failure of the builder to adjust accordingly, may be the problem.

 

[tonydutt]

Hmmmm. That is a good idea as joist hangers were not used from my initial scan near the access door. I will look closer when it is light outside.

Thanks many,

Tony

 

[unclesyd]

One thing not mentioned is the use of treated wood. If this was the common variety of treated pine you could have started out with a very high moisture level which in turn could have caused excessive shrinkage as the member dries. I have some 4x6 treated for ground contact that have shrunk 7/16" in the 6 direction after drying out in a shed out of the weather.

Another point about the cracking tile, on a Holmes on Homes show there was an episode where the title in a kitchen was cracking and the home owner was told that the floor was sagging and that was the problem. It turned out the problem was the installation of the "Hardie Board" as the tile underlayment using only drywall screw that allowed the board to flex which in turn caused the tile to crack on the grout lines.

You might want to look at the following sites concerning post jacks.

http://www.ellisok.com/ellisok/rescon.html

http://www.tigerbrandjackpost.com/super_s.htm

My old B&C textbook (1975) doesn't list 6x6 members as either joists or girders in floor construction. One other thing noted is all the tables are based on a 40 psf live loading for residential construction. .

 

[concretemasonry]

Too many people looking at old prescriptive tables reflecting only longer term loading.

It only takes one or two short term situations to crack the grout and cause additional later cracking. - It all goes to short term conditions and not design tables that rely on historic lumber of different sizes, grading and densities. The tables are not reliable for new growth lumber of mixed species.

Dick

 

[hokie66]

I think too much has been made of the fact that 6 x 6 members were used as the bearers. They probably don't appear in cookbook tables because it is an inefficient use of the material, but there is really nothing wrong with using a 6 x 6 on a short span, provided the stress and deflection are satisfactory.

The poor performance of the tiles may or may not be related to the unevenness of the floors. The underlayment (and fastening of such as unclesyd pointed out), the adhesive, and the grout could all be factors.

 

[hokie66]

Tony,
By the way, while I often suggest to DIY'ers that they need a structural engineer, I am not in the camp of those suggesting that you need one to figure this out. You seem to be doing just fine on your own, with a bit of help from your friends here. A mechanical engineer should have all the logical skills needed to investigate and decide.