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The previous owner of my property built a roughly 16x12 outbuilding on posts. Besides doing many things in slightly stupid ways, the building overall isn't awful. I've converted it into a manhut where I drink beers and butcher deers.

The floor bounces, and when I crawled underneath, I could have punched him. He used 2x6 floor joists, 19" on center. I dont have much working room under the building and am on a budget.

Here is my plan: cut holes in subflooring. Using auger or post hole diggers, bury 6x6 posts (3) in concrete, shoulder cut 6x6 and use 2x10s to create a beam in the middle of the joists. Think this will be enough to take out the bounce and be strong enough to have a couple of guys standing, along with lots of outdoors gear/equipment in there without risking breaking joists?enter image description here

Grade of soil shown in diagram. In the footprint diagram, the lowest clearance is in the top right corner. The ground slopes from top right towards bottom left.

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  • So the 2x6 floor joists span across the outbuilding (12’)?
    – Lee Sam
    Jul 16 '18 at 1:15
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    Where is this? Termites common? I'd use the truncated pyramid concrete blocks sold at HD and Lowes. They are designed to take 2x on edge or a 4x4 post on end. I'd slide them under from the outside. Forget about digging holes. Jul 16 '18 at 1:22
  • 2x6 spans entire building. In Pennsylvania. Hard freeze in winter.
    – Dennis8483
    Jul 16 '18 at 1:31
  • Termites are a thing here, but I usually see more carpenter ants than termites
    – Dennis8483
    Jul 16 '18 at 1:39
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I've installed beams in situations like you describe. It's not fun at all, and will probably be a lot more sweating and swearing than you anticipate.

I would be sistering the joists with 2x10s. They don't need to be the full length of the existing joists. As long as they are attached to the existing joists within a short distance of the end, they'll provide enough stiffness. You can probably do most of the work above by cutting channels in the subfloor near each side wall.

  1. Cut access channels in the subfloor fairly close to the side walls about 18 to 24 inches wide.
  2. Slide each joist, precut to roughly the same length as the original joists, but slightly shorter, into position from outside the building.
  3. From inside the building lift the joists into position alongside the original joists, working through the channels you cut in the subfloor. Use ratchet straps or an assistant to pull them up tight to the subfloor. Run a screw through the subfloor at each end to hold them in place.
  4. Bolt each end of the new joist to the corresponding end of the old joist. Run 2-1/2" screws into the new joist through the subfloor.
  5. Screw the strips of subfloor that you cut out earlier back into position. Float scrap lumber blocks underneath joints were appropriate to prevent flexing.

This will stiffen up the floor nicely, and you shouldn't have much in the way of squeaking. Certainly not so much that it'll be a problem for your man hut.

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    Good thing I love sweating and swearing. Thanks for the input
    – Dennis8483
    Jul 16 '18 at 2:57
  • You're welcome. Please take the tour to make sure you understand how this site works.
    – isherwood
    Jul 16 '18 at 3:00
  • Will do, been a lurker off and on for awhile.
    – Dennis8483
    Jul 16 '18 at 3:03
  • I've never done framing, but can't resist commenting. I have seen a lot of foundation repair over the years in my neighborhood, and nearly all of this is around the perimeter of slab foundations. (Some interior piers are retrofitted and they jackhammer holes in the slab?! 10x difficulty and problems.) Sistering joists when there is 4 inches of clearance on one side?! Surely the existing joists would be OK if they would be supported by beams, maybe only two, one on each side of the coal bunker. The beams could be slid in from the downhill side and then jacked to support the joists. Jul 16 '18 at 11:20
  • I'm not exactly sure what you're getting at, Jim. Yes, a single beam down the center would be more than adequate, but getting it up tight and setting posts under in with minimal clearance is difficult. Perhaps if the posts were outside the structure's current perimeter....
    – isherwood
    Jul 16 '18 at 13:13
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I like Isherwood ‘s idea about working from above, but not the “sistering” idea because you’ll need to excavate 5”-6” out from under the ENTIRE building AND requires a lot of lumber.

I like @JimStewart ‘s idea about adding a beam at mid-span of the existing joists.

I’m sure the existing floor is very springy, because 2x6’s at 16” o.c. spanning 12’ will support about 20 lbs. per square foot. Adding a single beam at mid-span will increase the strength of the floor to about 185 lbs. per square foot. (The code requires normal rooms to be 40 lbs. per square foot.)

Adding a beam at mid-beam will require a trench, but only at the beam not under the entire building. The trench “runs” with the slope, so it could easily be dug to drain.

The beam could be a 6x10 or 3-2x10’s. Or, it could be a 4x8 or 2-2x8’s if you installed a support at mid-spans and only had the beam span 8’ I like @JimStewart ‘s idea about anchoring the ends (which could also be installed from above). If the coal bin is in the way, I’d move the support inboard a foot or so and let the beam cantilever the last foot or so.

BTW, Isherwood ‘s notion of NOT extending the sistered joists to a bearing is not acceptable. This is why drilling holes through joists is unacceptable.

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  • Since this beam would be close to the soil shouldn't it be made with pressure treated 2x lumber nailed together? Wouldn't this be the cheapest decay resistant beam? After all this is not a critical application. Jul 16 '18 at 22:29
  • @JimStewart Yes, I like that idea...even if it has the required 6” clearance from the beam to the ground.
    – Lee Sam
    Jul 17 '18 at 0:18
  • There is a new method for raising concrete and might be possibly be used to raise supports: polyurethane jacking olshanfoundation.com/blog/mudjacking-or-polyurethane-injection/… Jul 17 '18 at 12:40
  • @JimStewart I don’t know if it could be effective for individual footings. Do you?
    – Lee Sam
    Jul 17 '18 at 15:55
  • After thinking about it, I do not think it would do for an individual footing. I just heard about this and couldn't resist interjecting this new discovery. Jul 17 '18 at 16:03
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If footings must go below the frost line, then I'd dig them at the edge, one on each side of the building in the middle of the 16 ft long side, and fill with concrete. Then use the truncated pyramid blocks, or other blocks on top to support a beam. Attach the beam loosely on to the joists above, then put jacks under each end and raise the beam (and the shed) until you can slide supporting blocks under the ends of the beam.

The particular footing I use from Lowes or HD has slots at a right angle for 2x lumber and a square for a 4x4 in the center. Here I am using one to support a cedar post (6"concrete base x 3.5") so I laid in a piece of PT 2x4 with notches cut out on the corners.

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  • Jim - will definitely consider... but have coal bin on one side of building and ground is sloped toward building. Even if I could move coal bin, might have 4 inches of clearance. Gonna be real tough to access. Other side of building has easy access
    – Dennis8483
    Jul 16 '18 at 1:48
  • Need a scale diagram. On the uphill side can you locate piers on either side of the coal bin? Jul 16 '18 at 8:35
  • Added diagram. Quick sketch by hand
    – Dennis8483
    Jul 16 '18 at 12:28
  • And the joists are parallel to the 16' side? Jul 16 '18 at 15:05
  • Joists run perpendicular to 16 side. On diagram, running from top to bottom.
    – Dennis8483
    Jul 16 '18 at 18:37

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