sonotube foundation

[rongaudier]

Does anyone have any actual experience building a sonotube foundation?

Here is my plan: Have 36" holes drilled along proposed foundation perimeter. The holes will be at least 48" deep.

Use a sonotube plastic bell mouth footing with 12" sonotube placed in drilled holes at appropriate intervals (yet to be determined).
Sonotubes will protude 18-36" above grade on sloped building site.

The proposed house is a 2 story 2x4 wood frame (www.houseplanguys.com #79-229).

I have several reasons for building this type of foundation:

1: I want to avoid disturbing natural water flow patterns around building site as much as possible. I believe this type of foundation will cause far less impact than a perimeter crawlspace or slab foundation.

2: By avoiding contact with ground, subterranian temites will be much easier to control (I live in Central Texas).

3: Underfloor access will allow for easier repairs and modifications to plumbing and other systems so routed.

4: I belive that by placing the footings for the sonotube piers at least 4 feet below grade I will avoid foundation movement caused by expansion and contraction of sub-surface clay deposits. (my thought is that the ground is more stable the further down one goes).

5: I believe this foundation will end up costing significantly less than other types (excluding conventional post and beam).

All comments are welcome

Thanks, Ron

[mjpliv]

The sono tubes you are placing in the ground and filling with concrete are not going to hold up the house. Its the soil underneath the sono tubes and concrete that actually holds up your house.

I know I am a long way from Texas but I would suspect there should be footings placed underneath your piers to provide enough bearing surface to support the weight of the structure unless they extend down to bedrock. Someone please correct me if I am wrong!

[rongaudier]

Oh yes, there will be footings. As I said in my first post I plant to use the plastic sonotube bell-mouth style footing (snaps onto end of sonotube). The footing is about 21" square. Apparently, the footing and sonotube are placed together in the hole, and then filled with concrete in one pour. An extra bell mouth footing can also be used as a funnel in the top of the sonotube when doing the pour. Naturally, I'll also use the appropriate rebar in the form.

[mjpliv]

Sorry about that, read that one too fast and missed it! :oops:

A couple of questions -

You mention installing sono tube pier all along the "foundation perimeter". Are there any interior bearing points?

Will you be relying on vertical rebar only in the piers or have they been speced with ties every 8 or 10 inches?

Will you be using any uplift restraints carried through to and including the roof assembly?

[rongaudier]

At this point I'm not sure of exactly how many piers I'm going to need and whether or not I will need interior load bearing points. The appoximate dimensions of the floor will be 24'x44' in a perfect rectangle. I was hoping I could simply space the piers in even intervals around the perimeter beams and then use 12" I-beam floor joists on 12" centers spanning the distance between the longitudinal beams wholly unsupported (about 23' 1/8" total span).

As far as the re-enforcement of the piers is concerned, yes I will use ties in the rebar.

Uplift restraints are a given as far as I'm concerned.

[mjpliv]

I just ran a 24' joist trough my TJI software. At that span with 12" centers you would need at least a 16" series 230 joist. Even thought it passes the deflection criteria of L/480 that deflection exceeds 1/2" in the center on live load only and over 1" under total load.

I would suggest adding a center beam and use smaller joists which will give you much better performance.

I would also suggest you shoot for 11' centers on your piers using a beam or structural rim to support the parameter and a center beam for mid point bearing also support at 11' centers.

[mjpliv]

If the center location for the beam doesn't fit the design, you should be able to jockey it around to line up with your bearing walls in the home.

[mjpliv]

I just had a llok at the plan set you mentioned - the center beam will not work

[rongaudier]

A center beam won't work? How come? This plan is approved for stem wall perimeter foundation as well as slab.

Actually, I was thinking I might need to support the centers of the floor joists due to the span. I've calculated 10 piers.
If you are interested here is the location of the footing info http://www.sonoco.com/topnav/products+and+services/industrial+packaging/engineered+carriers/ipd_tubebase.htm

Thanks for the info on the joists.

[mjpliv]

Its a two storey house (#79-229) and the walls supporting the second storey would not even bve close. Combine this with the fact you have some very large openings in (what I precieve to be) bearing walls then you will have some concentrated loads to deal with.

Give me a 10-15 minutes. I am working on it

[mjpliv]

Have a look at www.buildersmatrix.com/info/79-229.jpg and let me know if you understand the drawing

[rongaudier]

Wow, very intersting. I looks as though the second floor loads are transfered through the interior walls down to the first floor. Therefore, more support is needed in the points you have indicated. I don't understand exactly why there are additional piers under the living room floor where there are no load bearing walls located. Nor do I understand the uneven spacing around the perimeter. I suppose this is the result of some logarithm in your software.
I confess I'm not an engineer.
Thanks for your input.

[rongaudier]

Another question, are the additional piers located directly under the joists or are additional girders required in those locations?
I suppose I'm going to have to spring for the blue prints and see where they recommend additional support. Right now I'm in a very preliminary stage of planning.

[mjpliv]

The posts along the front varanda will support a drop beam (set back from the finished face so the lattice hides the concrete piers. This beam carries the porch joists (8') as well as the posts carrying the second story varanda.

The piers along the front face of the house carries a beam centered on the wall. This carries the living room joists running front to back as well as the other end of the porch/varanda joist which will be smaller and attched to the rim board of the floor system. The two end joists will probably be LVL lumber sized to carry your roof truss loads only because the floor loads in this area all go front to back.

from the stairs back, the joists change direction. The pier on either side wall carry a drop beam and are set back to accomodate lattice to hide the concrete piers. The joist cross a mid span drop beamthat is lined up with your stairwell opening (the one shown has 15 treads/16 rises and is sized for your 9' main floor ceilings)

Where the two interior drop beams meet, you will hang one from the other with an appropriate hanger. The large center space in the side-to-side interior beam lines up with the loads transmitted through the end of the walls by the stairwall and the entrance closets which is the open archway between the livingroom and dining area, this will probably be a 12" or larger LVL. Depending on who is designing the beams for you, the beam running front to back in the kitchen area may be able to stay at 9-1/2" and be buried in the ceiling.

As far as the rest of the piers go, they are spaced to give you decent support over a resonable distance. These spans can be adjusted to suit your final beam sizes. I really just wanted to give you a reasonable layout to accomodate the loads.

[mjpliv]

I should also mention that those dimensions are guestmates based on the rough plans availble on the website you mentioned.

[mjpliv]

in reply to the "additional piers" question -

The joists are completely supported by beams running under the floor assembly. The piers never really come in contact with the joists.

[mjpliv]

Clear as mud, Huh?

[rongaudier]

Wow that is amazing. Thanks alot. This sure gives me something to work with. I Guess 21 piers is workable, although I'd like to get away with less.
I'll print up and save your work. I'll keep you up to date with the progress of my project. Thanks again.
Ron

[mjpliv]

You can do it with maybe 3 less but you would have to bump up some beam sizes, one of which will extend into your 9' ceiling space in the kitchen.