Hello we are building a small off grid ICF home on our ranch in north Dallas. We are almost ready to pour the foundation but I wanted some feedback and opinions on the design. I am building this house for the long run and I'm willing to spend some extra now in hopes of it outlasting my wife and I. I have met with several concrete guys and so far have this design as the plan. I am extra interested in my footings and piers sizes and making sure they are more than enough. The house is about 800 sq. foot. Perfect rectangle, 35'x24'. The land where it is going to set will be flat after we bulldoze it. I am planing on having select fill brought in after that and we will build a pad and compact it along the way. I am currently thinking about a ten inch or twelve inch pad for drainage around the house. Do you guys think this is an OK height? I want to be able to walk out of my house with only one step if possible but don't want any drainage problems. The perimeter footing are 12"wx12"d and there will beams going through the middle of the slab both lengthwise and widthwise. (I will upload a pic later to be more clear about the channels and dimensions of everything) Do my footings need to be any deeper or wider? The concrete walls will be 6" wide. I was planning on a 4 inch slab on top. It will be monolithic slab. This will be a single story ICF home. I have been told to do anywhere from 3 inch to 6 inch. Also I'm doing concrete piers underneath. The current thought is 8 peirs around the perimeter. They will be 15 foot deep minimum...... On the corners and at the middle points of the walls where the beams running through the middle connect. I'm not sure what diameter to do these? I thought one contractor said to do 24 inch piers but those seem huge. I see alot of 12 inch is that the standard? The piers are pretty cheap to do so I want to make sure they are sufficient now, I don't want to have to jack up the house or anything later. We have very shifty soil here which is why I have added piers. Also for the ICF blocks I need to have rebar coming up out of the foundation to connect. Do I just wet set these? How far up should these stick out of the concrete and at what spacing? Do I need any extra around the corners or anything? I can't find much reading about this, I guess I could call a maker of ICF but I haven't 100% decided what brand I'm going to use, I will figure that out next. The slab will have #4 rebar and the footings #6. Should the piers be the bigger #6 rebar also I assume? Any and all thoughts and opinions are appreciated especially about the footing and piers as I have been told a couple different things. This is my start and I will adjust the design if needed. I'm hoping to have the dirt brought out at the beginning of the year and then I will let it weather for a couple weeks before digging my footings and drilling my piers. I'm sure I have forgot some info. that is needed and will ad more. I have also drawn the foundation on CAD but can't get a pic on here till my wife gets home. Thanks! Ryan

And I typed that out in neat paragraphs to make it easy to read but for some reason when I post it it spaces it in one giant paragraph which makes my detailed post hard to read and answer. Sorry

What internet browser are you using to type and make paragraphs?

Sounds like you are doing a post tension floor to the piers. That would put you under the guidance of the engineer.

The perimeter footings are actually a grade beams resting on the piers with the ICF wall resting on the graded beam.

A good engineer should be able to design the bottom courses of the ICF as the grade beam with no footing required but maybe the grade beam also contributes to the post tension.

If my assumptions are right, the pier (piling) diameter and numbers are part of the calculation of the weight of the house and the bearing capacity of the end of piling or its friction.

If the contractor says 24" it may be because there is no engineer involved and he is just making sure they are big enough. Not the right way to do it.

Posted By Alton on 11 Dec 2013 08:29 PM
What internet browser are you using to type and make paragraphs?

Google Chrome......i wish I could fix it it would be much easier to read. I'm sure my wife can I will get her to fix it and upload the pic I've drawn of the foundation to help make more sense of it all.

Be careful (ie, hire an engineer) before mixing different types of foundation support. Ie, you can create a monolithic floating slab (preferably post tensioned) that creates low psi on the soil or you can run piers down to stable soil and create beams to connect them. But some of each probably isn't what you want to do. Look into frost protected shallow (FPSF) designs (no footings required).

Removing the top soil and then filling the resulting hole with gravel is a good way to create a pond that will maximize the expansion of clay.

FBBP, thanks for the reply...

Not a post tension floor.....I don't like the idea of the cables under pressure and your right I would need more outside help and an engineer for that. It is a regular mono slab using rebar with concrete piers underneath the footings. They are friction piers. We have very shifty soil where I am.

Are you talking about an ICF foundation? I think thats where they use the ICF below grade straight on the footings or with no footing. I have read a little about that set up and elected to stay with a regular setup. I am just planning on using ICF for the walls on top of the slap....

like in the pictures of this arcticle I just found to show an example. This site actually helps with some of my rebar requirements.


http://lazarianworldhomes.com/our-buildings/construction-steps/

And I will get some more info on the size of the piers I could be wrong with that number 24". The house will be a single story with a very light roof. I am putting in the piers as insurance due to our shifty soil. I am meeting and talking to the concrete guy again about the numbers.

Posted By jonr on 12 Dec 2013 11:54 AM
Be careful (ie, hire an engineer) before mixing different types of foundation support. Ie, you can create a monolithic floating slab (preferably post tensioned) that creates low psi on the soil or you can run piers down to stable soil and create beams to connect them. But some of each probably isn't what you want to do. Look into frost protected shallow (FPSF) designs (no footings required).

Removing the top soil and then filling the resulting hole with gravel is a good way to create a pond that will maximize the expansion of clay.

I see what you are saying about mixing different supports. I thought a mono slab with friction piers under was pretty common? I can hire an engineer if needed and I do have a model house in the same area I can go get info from. I will ad more of that info. I will go and read about FPSF now, I know nothing about that. I was planning on a select fill mat raised for drainage. Where it is will be flat but I still have reason to be extra cautious with it. I was originally thinking 12 inch but I'm thinking about lower so my footings can be more cut in the ground.

Here is a case in Texas where the soil expanded and popped the house up from the piers. Pre-soaking the soil before pouring the foundation helps. Then you can get shrinkage, but this is OK if the slab can support itself.

Posted By jonr on 12 Dec 2013 02:01 PM
Here is a case in Texas where the soil expanded and popped the house up from the piers. Pre-soaking the soil before pouring the foundation helps. Then you can get shrinkage, but this is OK if the slab can support itself.

That is interesting and kinda scary but Is that pretty rare? I can easily soak it before we bring the pad. We are not in a big drought like that year and we are planning adequate drainage I hope and think. I can't imagine building a foundation where I am without piers. I see all the cookie cutter houses here and there is alot of foundation problems. One concrete guy said about my homesite he wouldn't do the job without piers underneath due to the soil.