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Beam and post foundation: no joists! (How to retrofit?)

Beam and post foundation: no joists! (How to retrofit?)

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  #1  
Old 11-07-19, 12:15 PM
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Beam and post foundation: no joists! (How to retrofit?)

My single-story home is approaching 60 years old. The foundation consists of only the concrete stem wall, 4x6 floor beams and 4x4 posts. There are no floor joists above the beams...just the subfloor, which I am estimating is slightly thicker than a typical subfloor over floor joists. (see sample photo below of a similar setup found online). Over time there has been settling in my home due to expansive soil. "Soft spots" have developed in my wood floor (typical oak) and a gap of about 1/16"~1/8" has developed between the tile floor of the bathroom and the baseboards. Bothersome creaking is heard below the kitchen tile floor and living room wood floor. I am also noting cracking of the tiles at the transition to the wood floor in the kitchen and bathroom. -- I wish to reinforce the floor and I am considering several options:

1) Install new 4x6 beams on posts parallel and in the span between the existing beams (approx. 5ft apart) in the areas where the soft spots are found. Net result would be beams every 2.5ft in areas where soft spots occur.

2) Add 2x6 members HORIZONTALLY between the existing beams, directly beneath the subfloor

3) Add 2ft x 2ft x 1" cut plywood squares in between the beams every 8 ft on new 4x4 posts + concrete piers

4) Just shim or replace the existing posts

Since the overall design of my foundation is apparently a bit different given there are no floor joists I'm trying to find out whether there is a standard approach to retrofitting/strengthening floors of this type that has been used elsewhere. Any insights would be greatly appreciated.

Many thanks in advance!!
 
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Last edited by MDSilverDIY; 11-07-19 at 12:42 PM.
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  #2  
Old 11-07-19, 12:34 PM
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How "proper" and legal do to intend to go?

My first thought is your idea of adding a new row of piers and a beam down the center of your existing span. Being in LA this would probably permits and I'm guessing the Inspections Dept. will want you to get an Engineer to design a fix, especially considering your seismic zone. In which case there isn't much point in asking online as you'll have to do what the Engineer comes up with. They might require proper footers and almost certainly attachment between your footers, piers and floor beams. My mind jumps to a couple thousand dollars in permits and engineering fees even before any work is done.
 
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Old 11-07-19, 01:03 PM
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Thank you Pilot Dane.

RE. "How 'proper' and legal do to intend to go?" given the fact I do not plan to move in the near future and i'm looking to place a DIY fix on an issue i'm experiencing my primary interest is in "proper". I had a foundation company look at my house and they had suggested a similar approach (ie. additional 4ft span post and beam) but I wanted to see whether there may be alternate approaches to this issue after learning about herringbone struts and horizontal blocking used to brace joists.
 

Last edited by MDSilverDIY; 11-07-19 at 02:44 PM.
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Old 11-07-19, 02:55 PM
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Set up a rotary laser in the crawlspace then jack and shim the existing posts using flat steel plates.
 
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Old 11-08-19, 03:41 AM
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Not sure what is going on here.

Is the floor sagging between the beams?
Or is it just that some of the supports/posts have sunk and are no longer supporting the floor?
Or both?
 
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Old 11-08-19, 10:19 AM
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Thank you Manden for your question. Yes...the floor appears to have some sagging whereby some beams are not well-supporting the subfloor or the subfloor is sagging in-between the beams. I believe the latter to be the case such that additional support of the subfloor is necessary. It's a pretty big gap between the beams/posts is it not?

My question is how to improve the support of the subfloor given the configuration (post and beam only).
 
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Old 11-08-19, 10:23 AM
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Thank you XSleeper for your suggestion. I'll see if I can find a rotary laser for rent.
 
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Old 11-08-19, 11:11 AM
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If doing this yourself I would do a combination. With the rotary laser find the sagging spots, jack and install steel shims under the existing piers.

Sagging of the subflooring may be difficult to remedy. Best would be to run another beam down the center splitting the span and having it's own piers. You will have to be a little careful when jacking the new beam and taking out sag. Don't be surprised if you need to jack some then let it sit for a few days and jack some more. You don't want to go too much too quickly and start pulling the subflooring up off the beams.
 
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Old 11-08-19, 01:18 PM
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Do you have as much head room as shown in your example picture?
If yes then I would try the following.
Get a couple bottle jacks. You may end up needing 4 of them.
Make an H out of 2X6 possibly double them up.
Put joist hangers on the ends.
Raise this up between the beams. Doing this may take some ingenuity.
Get one side where the top edge of the H is level with the beam and attach it to the beam with the joist hanger.
Now raise the other side until it also lines up with the other beam.
Do this slowly so it may take at least a couple days or more.

Once it is up there and the sag is gone attach that sides joist hangers to the beam.

Or you could try just jacking up on the center beam of the H.

Then move down the space making T's with joist hangers on all ends.

A beam would be better but may not be feasible for you to do.
Also if you have some supports that have sunk you have no guarantee the the new ones will not sink so you would have to check them periodically.

The only thing I am unsure of is how long the center of the H could be but I am sure other will chime in with suggestions the above is just how I would tackle it.
 
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Old 11-11-19, 08:07 PM
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Thanks Pilot Dane for the sage advice. Given the approx. 5 ft span between the beams a beam midway in between will certainly help if taken slowly. I was down there today and took note that there must have been some termite action in some places, which further weakened the subfloor across the 5' span. Definitely needs another beam!
 
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Old 11-11-19, 08:12 PM
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Manden...unfortunately the photo I provided is just a sample of my configuration. In fact I only have about 12~15" under my floors. It's a rough working environment. Was down there today and got awfully discouraged thinking about trying to maneuver beams and posts and laser levels and tools, etc. Need to plan very well so not an ounce of energy is wasted if I choose to go at this on my own. Thanks for the idea...basically use 4x6's as the joists between the beams. Got it!
 
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Old 11-12-19, 05:02 AM
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When facing a lot of tight crawl space work I often cover the floor with plastic as a first step. Here (in NC) plastic is often a good idea for moisture control and having it down makes it much easier and cleaner to move around when working.

Crawling back and forth transporting tools and materials can be very tiring. I have a heavy duty tote that I put my tools in. I put a rope on both ends of the tote and load it up with my tools. Tie one rope outside or near the crawl space opening. Then bring the other rope end with you when you crawl back. Then pull the rope to bring your tools. That way you don't have to crawl and carry.

Then once in the work area tie off that end of the rope. Now with both ends tied off you can send the tote back and forth without loosing the end of the rope. You can also untie the rope from the tote and tie it to materials to bring back.

For big heavy stuff a child's plastic snow sled can help. Even if you just put the nose end of a beam on the sled it will keep the front from digging in as you drag it back.

Don't skimp on light. Lights are one of the first things I bring in and I leave them under while the project is under way. With good light you can work faster and you don't misread measurements. It's also good for keeping scary goblins (snakes in my area) at bay.
 
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Old 11-15-19, 10:34 PM
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Wow! Sage advice there Pilot Dane. Thank you. I've thought about using an older masonry tub to pull things behind me with a rope tied to my foot, but the sled idea sounds even better (already has a rope or handle on one end). Really appreciate the insights.
 
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