School me on pier and beam setups

[asphaltjunkie]

Standard post setting is 3x diameter of your post and minimum 1/3 of the post buried in the ground. Gravel in the bottom of the hole, set the post, then concrete it.

Ok, next question. Since this will be a house and not just a deck, should I stick to the 6x6 sized posts as originally planned, or will 4x4 posts be adequate?

[8mpg]

Ok, next question. Since this will be a house and not just a deck, should I stick to the 6x6 sized posts as originally planned, or will 4x4 posts be adequate?

Thats up to you... with the cost difference being next to nothing, might as well beef it up.

[asphaltjunkie]

Here is my initial plan on post setup/location. Questions and info are in the pic if you can read my handwriting lol

[Blackpony]

Also I could be wrong, but I believe I read somewhere that even with a piered slab setup like 8mpg mentioned you can still have it settle some in certain kinds of dirt. I am certain I read the only way to prevent it (except with something like a large earthquake) is to put the concrete piers on bedrock, which could be fairly shallow and cheap, or deap and expensive. I could be wrong but I read or heard that somewhere. Basically I am saying it is hard to never have any settling or shifting.

This is what my builder said he will be doing to our foundation. It will be a pier and beam with post tension cables. Each pier will be drilled until it hits bedrock. He said there will be a variance in the depth, some may be 10 feet some may be 30-40 feet it just depends on the area. But that is how he has been doing them for many years and never once has his clients needed any foundation work.

[8mpg]

I would put the beams long ways...just use a span table to figure out the right sizing. Im pretty sure you will have to split the 24' side to make sure you put a pier/post right in the middle and use 12' beams. You can use something like a fish plate to join them or you can get longer beams and cut a shoulder and overlap them.

These old school carpenters are awesome. Watch all their videos on framing. It will cover just about everything you need to know.



I wonder why these guys didnt sink wood into the ground...

[black2002ls]

This is what my builder said he will be doing to our foundation. It will be a pier and beam with post tension cables. Each pier will be drilled until it hits bedrock. He said there will be a variance in the depth, some may be 10 feet some may be 30-40 feet it just depends on the area. But that is how he has been doing them for many years and never once has his clients needed any foundation work.

A quick google didn't return anything. How does this work? We use post tension cables in our slab foundations. This helps reduce/stop the slab from coming apart. The foundation make up looks like a waffle and cables are ran through the beams, throughout the slab, etc and then stressed 7-10 days after we pour concrete.

I can't see the benefit/use in a pier set up. Anyone have some insight?

[Blackpony]

A quick google didn't return anything. How does this work? We use post tension cables in our slab foundations. This helps reduce/stop the slab from coming apart. The foundation make up looks like a waffle and cables are ran through the beams, throughout the slab, etc and then stressed 7-10 days after we pour concrete.

I can't see the benefit/use in a pier set up. Anyone have some insight?

My understanding is it helps support the foundation to prevent it from dropping should the ground settle. I have heard arguments on both sides as to wether a post tension cable foundation needs piers or not. My builder recommends them as added insurance.

[black2002ls]

My understanding is it helps support the foundation to prevent it from dropping should the ground settle. I have heard arguments on both sides as to wether a post tension cable foundation needs piers or not. My builder recommends them as added insurance.

So it is a concrete slab, on piers? Not a pier and beam?

Post tension cables help prevent the house from "breaking" when it settles and moves. We have piered a lot of homes that have post tension cables. It all has to do with the way the ground moves beneath the foundation. The cables hold the slab together when it cracks, because it is going to crack, there is no way around that. We will pre-pier a house if the soil report shows that it is needed, or if a certain amount of fill dirt was used in that particular part of a subdivision when it was developed.

We also run into instances where we have to pier between years 5 and 10 (we provide a 10 year structural/foundation warranty) due to excessive movement that has caused the house to have issues.

If you can fit it into the budget to pour piers before you pour the slab, do it!

[Blackpony]

So it is a concrete slab, on piers? Not a pier and beam?

Post tension cables help prevent the house from "breaking" when it settles and moves. We have piered a lot of homes that have post tension cables. It all has to do with the way the ground moves beneath the foundation. The cables hold the slab together when it cracks, because it is going to crack, there is no way around that. We will pre-pier a house if the soil report shows that it is needed, or if a certain amount of fill dirt was used in that particular part of a subdivision when it was developed.

We also run into instances where we have to pier between years 5 and 10 (we provide a 10 year structural/foundation warranty) due to excessive movement that has caused the house to have issues.

If you can fit it into the budget to pour piers before you pour the slab, do it!

Yea it will be a "waffle" look with concrete beams and post tension cables. But we will be adding piers under it before pouring.
Yessir my builder said he won't build it without piers. The dirt in our area is a black clay that he said expands and contracts a huge amount. We are waiting on the engineered foundation plans right now so we can get started.

[dcs13]

Can you use steel ? This is similar in size that you are building. Its a barn I built 2 years ago. The posts are 4 feet in ground. Steel prices have come down.

Finished project:

[black2002ls]

Good ol' black clay. We look at PVR (potential vertical rise) reports for each subdivision to determine if we need to pier a house or not. I don't have much to do with that though. Our engineering separtment handles that!

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[juiceweezl]

A quick google didn't return anything. How does this work? We use post tension cables in our slab foundations. This helps reduce/stop the slab from coming apart. The foundation make up looks like a waffle and cables are ran through the beams, throughout the slab, etc and then stressed 7-10 days after we pour concrete.

I can't see the benefit/use in a pier set up. Anyone have some insight?

Resists settling. Basically the slab is supported by the compacted soil, but it also has beams (the waffle) designed that bear on piers. If the soil settles, the beams support the slab and transfer load to the piers.

My understanding is it helps support the foundation to prevent it from dropping should the ground settle. I have heard arguments on both sides as to wether a post tension cable foundation needs piers or not. My builder recommends them as added insurance.

Correct.

So it is a concrete slab, on piers? Not a pier and beam?

Post tension cables help prevent the house from "breaking" when it settles and moves. We have piered a lot of homes that have post tension cables. It all has to do with the way the ground moves beneath the foundation. The cables hold the slab together when it cracks, because it is going to crack, there is no way around that.

Correct for the most part. Post tension cables work to hold the slab together. In a true slab (not the waffle above), you can expect lateral movement, but it will be the entire slab together. The cables help to resist cracking by holding it together, much like if you just had a compression sleeve around it.

We will pre-pier a house if the soil report shows that it is needed, or if a certain amount of fill dirt was used in that particular part of a subdivision when it was developed.

If you can fit it into the budget to pour piers before you pour the slab, do it!

Yes to both of these.

Yea it will be a "waffle" look with concrete beams and post tension cables. But we will be adding piers under it before pouring.
Yessir my builder said he won't build it without piers. The dirt in our area is a black clay that he said expands and contracts a huge amount. We are waiting on the engineered foundation plans right now so we can get started.

Correct and smart builder. The soil isn't as bad as everyone makes it to be, but I'm a believer in do it right and do it once.

[juiceweezl]

I would put the beams long ways...just use a span table to figure out the right sizing. Im pretty sure you will have to split the 24' side to make sure you put a pier/post right in the middle and use 12' beams. You can use something like a fish plate to join them or you can get longer beams and cut a shoulder and overlap them.

These old school carpenters are awesome. Watch all their videos on framing. It will cover just about everything you need to know.



I wonder why these guys didnt sink wood into the ground...

Because it's a crawlspace and not a post/pier and beam foundation. But you already know that, right? In a crawlspace, and the lateral resistance is taken at the perimeter where there are grout-filled, reinforced CMU that are sitting on a concrete footing. The interior posts are simply done to provide intermediate support for the floor system thus reducing the tributary area and then allowing for smaller sized framing in the floor. They are only supporting axial loads, so no need for a moment connection. That's why they didn't sink the wood into the ground.

[black2002ls]

My first comment asking how it worked was more referencing pier and beam. I have generally heard pier and beam refer to elevated wood framed foundations. I can see how a modern post tension slab set on piers could be referred to as pier and beam, it just isn't common in my circle.

Side bar, have you ever seen a cable blow out? They will do some crazy stuff! We are dealing with a broken cable now on a house that is set to close in 2 weeks. Going to have to pull the driveway to get it replaced. It is one of the main tendons in the slab.. :/

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[8mpg]

Because it's a crawlspace and not a post/pier and beam foundation. But you already know that, right? In a crawlspace, and the lateral resistance is taken at the perimeter where there are grout-filled, reinforced CMU that are sitting on a concrete footing. The interior posts are simply done to provide intermediate support for the floor system thus reducing the tributary area and then allowing for smaller sized framing in the floor. They are only supporting axial loads, so no need for a moment connection. That's why they didn't sink the wood into the ground.

Guess Im the only one that considers crawl space a pier and beam...