Pier Foundation in Texas Hill Country Rocky Soil

Started by Dream2Reality, June 15, 2017, 03:51:52 PM

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Dream2Reality

I found an old post about building a foundation in rocky soil.  One of the replies was from Chateau Prideaux and I was hoping for more information from this person since I am also building in the Texas Hill Country.  I have spent hours researching my options and still can't get a straight answer.  At this point my husband and I want to build a 20x40 on pier and beam but are considering going smaller if it means we can do most of the work ourselves and keep out of debt doing it.  I have no idea how deep to set the piers, what size diameter to use, or how close to space them.  Any information that can help us get started would be appreciated.  Our desired build site is on a small hill and very rocky.  We are in hot Texas where freezing isn't an issue.  We are on a very wooded lot and would prefer to keep as many of the trees as possible.  Thank you - I should add that there are no building restrictions/requirements.

Don_P

Those are important questions to have correctly answered when building on piers. They should be answered by a local engineer rather than by someone telling you what you want to hear on an internet forum. That is also why that type of construction isn't covered in the prescriptive codes but falls under the provisions of engineered construction. Being exempt from building requirements unfortunately doesn't suspend the laws of nature which is what those parts of the building code are based on. I understand that is not the answer you were hoping for and I'm sure someone will chime in with what they think works just fine. I also suspect you really know better than that. An engineer designing this is the best way to go.


ChugiakTinkerer

Hello and welcome to the forum!  There's really no limitation on how much work and sweat equity you can put into building your house, regardless of the type of foundation you want to build.  Pier foundations are great for small structures, but when you start scaling up the building it soon gets to a point where other construction methods are about as economical, and have the benefit of providing much better support for your house.

A foundation needs to do two things.  First, it needs to distribute the weight of the house into the ground evenly so there is no settling or cracking of the structure.  Second, it needs to anchor the house to withstand the forces of nature such as earthquakes, high winds, etc.  Pier foundations can do the first one adequately, provided they are built with big enough footings.  But they do a poor job on withstanding the forces of nature.  In order to make them strong enough, folks end up putting in diagonal bracing and shear panels which ends up being as much work as just building a continuous foundation but doesn't perform as well.

You don't see information that answers your questions because they can't be answered without knowing specific details about your build.  The size and construction method of your house, the engineering properties of the soil, and the environmental conditions at the property all must be taken into account.  If they aren't addressed adequately, you could end up with a house that shake in the wind, settles unevenly due to soft ground, or worse.

Plenty of folks here have dug and poured their own footings and built up a stem wall of concrete masonry units (CMU, also known as cinder blocks).  Another alternative that can be done by investing a lot of sweat equity is a permanent wood foundation.  I don't know if that's viable in your part of the country, but I implore you to consider any of the continuous foundation designs that have been proven over the decades.  Even with a poured concrete foundation you can do most, if not all, of the earthwork, saving the funds for the concrete truck.

If you're wanting to build a home that you and your loved ones can live in comfortably for years to come, it is in your best interest to start with a solid foundation.  A pier and beam foundation can be that, if it is done right.  But doing it right usually means spending more money and time than originally intended.
My cabin build thread: Alaskan remote 16x28 1.5 story

Dream2Reality

Thank you very much for those responses.  Everyone makes building a house seem so straight forward and yet I don't even know how to get started.  I'm not even sure who to contact locally for help.  When I call they want me to go through a contractor.  I figured I would see what I could find out from others who have gone down this road before me.  We have certainly considered and continue to accept all possible methods and options.  We may even skip the foundation and move into a bus! lol Thank you for your input.  It is appreciated!

UK4X4

If you wander around in here, at the beginning of a lot of threads all discuss foundations...I too was looking at pier and beam,,,but through time, effort and multiple discussions read in here  realised that it was not a recommended or suitable foundation for my size of house on my property.

20 x 40 is quite a large structure when you starting adding up all the loads involved.

Roof- upper floor- lower floor furniture people etc etc all add weight...this weight needs to be supported by the ground.....each type of ground has a different psi associated with it.....psi is pounds per square inch...

ie the weight it can support.

you need to start from the roof down calculating all the roof and floor loads ----rather than repost the method .....see post 7 on this thread     http://countryplans.com/smf/index.php?topic=14614.0

Most standard foundation methods can be easily built by hand, a cement mixer and a lot of graft.........many choose to sub out the foundation and then do the build themselves.

Bigfoot publish their weight charts for pier supports.....but by the time you've dug so many holes a standard perimeter foundation usually starts to become more sense.

Post some pics of the land and your basic design your considering then assistance can be given


jsahara24

Quote from: UK4X4 on June 16, 2017, 08:16:04 AM
Bigfoot publish their weight charts for pier supports.....but by the time you've dug so many holes a standard perimeter foundation usually starts to become more sense.

I agree with the above.  In my mind I initially thought the benefit of using piers is you don't need a backhoe as you can dig the holes with a post hole digger.  Unfortunately, when you start to calculate building loads you will quickly realize you need footers beneath the piers.  So now you are left with needing a backhoe to dig it anyway. 

So my next thought was I can rent a backhoe for a day, dig for my footers, set my bigfoots and sonotubes and have the concrete poured the next day.  Which is actually what I did.  But by the time I had everything dug out there was barely any dirt between my pier holes.  I do wish I went with a full perimeter foundation, it is my biggest regret in the cabin building process. 

However, using the bigfoots with sonotubes is, in my opinion, the best way to use piers.  I went about 5' below the surface, put rebar in and have a monolithic footer/pier which certainly assists in resisting lateral stresses.  However it will never be able to match a continuous perimeter foundation.  I then set my beams directly on the concrete piers and I have had no issues with my setup.  My soils are gravel/sand which has a much higher strength than clay/silt, and it allows water to drain easily. 

I also built in an area which doesn't see major hurricanes, tornadoes, earthquakes, etc. 

To summarize, id recommend doing a full foundation.  Whether its poured concrete walls, cinder blocks, slab on grade, precast concrete walls, etc.  However it will definitely cost you more money upfront, and I would definitely recommend against 4x4's or 6x6 posts. 

Good Luck!

icanreachit

So from building in central Texas I can tell you the two general rules of thumb, with the clause of, "consult a structural engineer". They're cheap and worth every penny.

With that said for slab on grade the beams usually must penetrate 30" or until you hit rock.

As pier is point load vs distributed, what size your piers needs to be will vary. Obviously, if you hit rock, great, but you still need to know the diameter of your piers.

Cheers