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Old 02-20-2010, 10:32 AM   #1
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Adding piers under beam


I have a couple of existing 4X6 beams that span about 11 feet. I'd like to add an additional pier under each for more support. I can easily dig down to firm, undisturbed soil within 1 to 2 feet. This location is under the house and it stays dry. This is a crawl space so there isn't a lot of working room... not too bad though, maybe about 20 inches.

Questions:
1. Is it sufficient to just dig down to undisturbed soil even if it's only 1 foot or should I go deeper? 18 inches? 24 inches?
2. What are some ideas for building a form that will still allow me to pour in the limited crawl space?

Thanks, David

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Old 02-20-2010, 11:09 AM   #2
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Adding piers under beam


where are you?

grout pump.

if you dig down only 12 inches or so, expect to be adjusting the pier annually with shims due to heaving if you are in a frost area.

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Old 02-20-2010, 11:26 AM   #3
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SF Bay Area... frost here is very rare and very limited. Soil never freezes.
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Old 02-20-2010, 06:52 PM   #4
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Quote:
Originally Posted by davidr222 View Post
Questions:
1. Is it sufficient to just dig down to undisturbed soil even if it's only 1 foot or should I go deeper? 18 inches? 24 inches?
2. What are some ideas for building a form that will still allow me to pour in the limited crawl space?

Thanks, David
Because of where you are, it has to be seismic code compliant.
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Old 02-21-2010, 01:05 AM   #5
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Adding piers under beam


The earlier respondents are quite correct that you must meet all your local building code requirements, and there is probably little downside to calling your building department and asking a few questions (although I don't know your building department).

But, if I lived in a world without such concerns, I would:
  1. Dig a footing hole that was a least 1' square at the bottom to a depth at least 1' below the frost line or below grade.
  2. If the hole is tight enough, I would skip building a form and use the earth as the form. If the hole was too big, I would build an appropriately sized box out of just about anything convenient and use the excavated dirt to back fill around the box. Or you can buy sonotube, or you can line a milk crate with a trash bag, or whatever... The dirt is usually enough to counter balance the weight of the concrete so you don't need to worry too much about the form's construction. If you have 20" clearance, I would imagine you don't need to build the form in place. The form can stay in place when you are done.
  3. Buy enough bag concrete to fill that hole, a post cap, post base, post and fasteners.
  4. Pre cut and assemble the post to the base and cap. Attach the hardware tight to the post.
  5. Work with a friend to attach the post assembly to the beam so that is as snug as possible, meaning tight, to the beam. When you are done it is hanging above the footing hole.
  6. Use a bottle jack on a large flat block (a length of 4x12?) to raise the beam about 1/8" above its current location, or if the beam is sagging, put a string on the beam and jack it to straight plus 1/8".
  7. Mix and pour the concrete as close to the crawl as you can and haul the mix to the footing in 5 gal pails.
  8. Use a small level to make sure you are putting the post in plumb.
  9. After the concrete has cured for a day, remove the jack.
If wanted to be exercise greater caution, my footing would get deeper and wider, I would add re-bar, and I would buy bigger, heavier duty caps and bases. If this was only to address a sagging floor, I wouldn't go too far down that road. If it had to do with the structural integrity of the house, I would.

Have fun,
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Last edited by Rory Read; 02-21-2010 at 01:07 AM. Reason: too vs to, it's late
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Old 02-21-2010, 08:17 AM   #6
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Adding piers under beam


#5 answer looks good as this is an existing structure that you are just trying to beef up a beam or two. Go for it.
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Old 02-21-2010, 10:49 AM   #7
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Adding piers under beam


You may be able to save some time and effort by purchasing precast concrete piers, in your case about 1 foot square. You can buy them in 6 inch thick increments. You dig your footing, stack the piers, and as previously noted you jack up the beam a small amount, and set the precast piers tight up against the top. If you can't get them tight, you can shim them.

As for depth, the deeper the footing, the less settlement your are going to get. Also, as previously noted, you are not building a reinforced column here, so you are only getting a friction fit. These piers will be effectively useless in an earthquake. To make an earthquake resistant column would require a carefully designed footing, with a properly designed and constructed connection to the beam. Kicks the project into a whole different level of complexity.

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