Newbie Starting a Pier and Beam cabin in TX

Started by Trantius_Rune, July 12, 2017, 08:39:05 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Trantius_Rune

Hello!
   I've enjoyed much of the awesome info I've found on here and am finally about to dig some holes to start my own 30x50 pier and beam cabin. One question I've got that makes me a little nervous is just how deep should I put my piers? The frostline is only 4ish inches deep but the clay content of my soil is fairly high for the top 3-4' though I am above the wolfe city sands formation so there's a healthy mix of sand in there the deeper I go. I feel like I am over thinking this a bit and would love some experienced feedback on whether I should go ahead and dig dig dig, or do sonotubes on 5 gal buckets cut it just fine in clay soils.

Thanks!
-Trantius Rune
Ellis county, TX

Don_P

 w*
If you google  pier foundation repair companies I suspect most will be in TX. Which I suppose means when this fails help isn't too far away. At 30x50 this is more than a light little cabin. Footings should never be less than 12" deep but should be on stable soils. With all that said I think you should be looking to local wisdom of what works with your soils.


ChugiakTinkerer

Hi Trantius_Rune, welcome to the forum!

The economy one gets with a pier foundation, in both time and cost, typically vanishes as you scale up the size of the structure.  If you're going to invest tens of thousands, if not hundreds of thousands, into building a place then you'll probably want to make sure it has a solid foundation.  if you are unsure of what is needed in your local area, you could consult an engineer.  That would be an upfront cost that will pay dividends down the road.

if there is a jurisdictional authority where you want to build, you will need to comply with the local code requirements.  That usually means building an approved continuous perimeter foundation as prescribed in the residential code, or having plans that are designed and stamped by an engineer licensed in your state.  Pier foundations can be done right, such that you never have to call the repair guys that Don P mentioned.  Or they can be done cheaply.  From what I've read on this and other web sites, trying for both never works.
My cabin build thread: Alaskan remote 16x28 1.5 story

icanreachit

Hi Trantius,

I'm not sure what the county requires but I have done slab on grade in Austin and have family in Dallas. In Austin we just go till we hit bedrock because it's usually no more than 30 inches. With Pier you just increase the pier size based on the load bearing capacity of the soil. With that said, Don_P is correct. However, Dallas has a lot more Clay than Austin. I would dig a few test holes to see how far down your bedrock is to see if you need to contact an engineer. They're cheap for what they do.

Trantius_Rune

Thanks for the feedback everyone, I'm really looking to do this as much I can on my own. With that being said I do like the idea of passing my plans by a structural engineer to make sure I'm not doing anything stupid or that I'll regret later. The biggest reason I'm looking to go with a pier and beam foundation over a concrete foundation is that I've had to deal with a slab leak in a former home and a foundation that settled unevenly (by about a 6inch difference) in another. I have no illusions about any foundation being perfect in my region of Texas due to the amount of clay we have to deal with, but being able to jack and re-level a pier and beam or climb under and fix plumbing makes any extra cost feel worth it to me.

I've done some more digging too and according to the usda's websoilsurvey I'm on top of Clay Loam 28-40" PZ, which if I'm reading it right should be considered a type A soil with compressive strength of about 1.5 tons per square foot or greater.

I'm also looking to build this on an old terraced section of land (all of the building will fall well within one terrace) but from one of the high corners to the two low corners is about a 1-2ft difference in elevation. I've been leaning towards using 12" sonotubes along my outer walls and then maybe dropping to 8" sonotubes on the interior piers with 3 joined 2x10s as beams. The current plan is to assemble one of those steel kit homes on top of the pier and beam foundation and then finish out the rest as I go.

The county we live in really only requires a building permit and doesn't care about much else unless you plan to make it a business. I'd still like to stick to code as much as possible though considering they are there for very good reasons most of the time.


icanreachit

Hey Trantius. Sounds great with the city! You may be able to go smaller than 12" with the compressive strength of clay, but that's where the engineer comes in (though there's probably a table somewhere, not saying you can't). However, I know that the expansive power of it is impressive so it may still be good to at least get down to caliche.

LatinForLiar

You need to make sure you have enough piers given the fact that you're on clay. Also remember you need to find undisturbed ground. Be careful, if it was terraced, it might not be virgin soil).

Add up the weight of the floor, ceiling, roof, and walls, and then figure out how many square feet of foundation on 2,500 lb clay you need to support it.

It may end up being easier to do a short foundation wall.



Don_P

That accounts for vertical loading but not lateral... wind/seismic. That is the reason for either doing a full perimeter foundation of bracing walls or calling in an engineer for an unbraced foundation like this.

Dave Sparks

Many counties do a plan check once you open the permit. Many will take a look before you pay and let you know if you are in the ball park.
Bring them a Pizza and tell them there is no rush but please check my plan. I have worked in a few counties that only want aged Whiskey :P
"we go where the power lines don't"


icanreachit

Quote from: Dave Sparks on July 16, 2017, 04:23:48 PM
Many counties do a plan check once you open the permit. Many will take a look before you pay and let you know if you are in the ball park.
Bring them a Pizza and tell them there is no rush but please check my plan. I have worked in a few counties that only want aged Whiskey :P

Dave that's a good point. Ours has a $60 fee but it's money well spent. The woman who went over my plan was an architect for 12 years beforehand. She had a lot of great advice. Also, she probably wouldn't have rejected a bottle of whisky.

Don_P

More often than not plan review actually happens at the rough in inspection, if then. I have a hard time looking upon them as qualified oversight in most cases, more so as you get out into the country. They also have no skin in the game, your engineer has his license and insurance on his work. The inspector is exempt from any responsibility by law. "Building to code" is a shorthand for building according to accepted engineering practices, which is what the structural parts of the code are based on. Building for the inspector is at best a very mixed bag, some know what they are doing, many do not.

icanreachit

Quote from: Don_P on July 16, 2017, 07:10:25 PM
More often than not plan review actually happens at the rough in inspection, if then. I have a hard time looking upon them as qualified oversight in most cases, more so as you get out into the country. They also have no skin in the game, your engineer has his license and insurance on his work. The inspector is exempt from any responsibility by law. "Building to code" is a shorthand for building according to accepted engineering practices, which is what the structural parts of the code are based on. Building for the inspector is at best a very mixed bag, some know what they are doing, many do not.

Don, I've had problems with that in the past. One guy didn't like my plumbing because it's not what he would have done. I had to walk him through it in order to get him to pass me. He initially wanted me to cut it out and do it his way. He was not a plumber, but I needed him to sign off on it to move on.