Questions about building a concrete pier

[Arky217]

Don't know if this will help you any, but this is how I did my foundation.
I chose post & pier because:
1) I needed an inexpensive foundation that I could do myself.
2) Could not get a concrete truck to the location.
3) My location was on a mountain ridge and the soil is very solid and very rocky.

I dug the holes by hand, and just as well as the ground was too rocky for an auger.
(Had to use a rock bar to bust up the rocks after the first few inches)
My frost depth is only 6"; the holes piers are 18" below ground and 3" above.
The piers conical; 10" dia. at the top and about 16" to 18" at the bottom.

I used just one piece of vertical 5/8" rebar with a flat plate welded onto the end.
Through a hole in the plate, the posts and braces are bolted together with 1/2" bolts.

I milled all my lumber on a chainsaw mill; the posts are the red heart out of cedar (rot and termite resistant) and the rest is yellow pine.

The beams are 6"x8"x12'; they span 6' from post to post.
Total of 36 posts; average height is 30".
The house size is 24'x48'.

Arky

[John Raabe]

Nice work! Looks solid and well braced. Bolts with washers are good way to make those connections.

[bob57434]

My thinking on using the blocks was to give the tube something to rest on and save concrete (I have a few old cinder blocks up there).  Also, I can only find tubes that are a max 4' so they won't go all the way to the bottom.  It does make more sense and would be a little easier not to use the blocks at all...  What would the minimum dimensions of the base of the footer be?  I guess it doesn't need to be 24" thick, that took a lot of concrete...

[bob57434]

Arky - I like that.  What is a chainsaw mill?

[MountainDon]

From the original post....

Hi, I don't have much construction experience and I'm kind of learning as I go. 

Building just about anything can be a rewarding experience. From where we are at this point it is my personal belief that there should be a temporary halt in construction. That should be followed by a review of the plans. There should be plans and not simply ideas in someone's head, IMO. I can not conceive of building anything without having drawings illustrating the project. Maybe it's just me but I draw out pretty much everything I build, be it a simple box or a building. Some of the drawings are simple, some more detailed.

What kind of structure is to be built? Type of roof? Type of walls? Type of floor? Then comes what type of foundation?  Yes think it out backwards first we we have some idea of what we're looking at, what is needed to make this structure just once. Will there be porches or decks? All these parts interact and need to interact safely. There is no point, IMO, of rediscovering the wheel, so to speak, when this has all been done before. Many times it has been done wrong which is a waste of time, effort and materials. Sometimes original errors can be corrected without too much effort. Sometimes they can not be fixed without greater effort and expense. I could point to a few projects that have needed remedial work part way through, but won't embarrass the owner-builders.

Anyhow that is my opinion for what it is worth.

[alex trent]

Wow..Arky, some job.....piers for a big place. Looks picture perfect.

Bob..listen to MtnDon. You really do need a plan first.  Look at Arky's stuff and compare to what you are stumbling through.  I was not far ahead of you when I came on here and started.  But..but..but..I did it all well before I started and changed before I pour or nailed anything.  I worked on it for about two months and honestly you have to do a bit of work. Google some on the subjects, get some input and then come on here and ask bout what you PLAN to do, not ask for basic info. Works better the way s you then get real world critique of what you get online.

The early part of my project is a lot better than the latter part because i spent more time planning the early sections and got behind on that later on, so I was doing stuff as I was asking.

You are getting some negative feedback, but don't get discouraged...it gets easier when you draw it out.

[bob57434]

That sounds smart - lol I might not have much of a choice, I think I broke my wrist at work today.

[Don_P]

Crap!
I've broken 3 of em. If you think you did, you did. It is not a tore down kind of pain. Go get it x rayed tomorrow or you're just grinding things up.

[bob57434]

So the good news is I only sprained my wrist so I won't be out of commission too long. I've been working on my plans, I'm exited to get some feedback on them.

I had an idea about that first pier I made which wobbles. What if I added some lateral strength to it by connecting it to the two adjoining piers with allthread or some kind of metal rod. The rod would go through both piers and have a pair of nuts on both sides of each pier. Sound stable enough?

[MountainDon]

A pier is the base for everything else. I don't like the idea of applying band aids there.

[alex trent]

And the band aids you propose sound lousy anyway.  And likely more trouble than they are worth.

[Squirl]

3. What exactly is the definition of a "footer"?

Don did a really great post under the IRC and best practices part of the forum.  I third the recommendations to take a break and plan out the building.
http://countryplans.com/smf/index.php?topic=10675.0
You can also find links to the IRC in parts of this sub category.  The nice part about is it gives a free written and sometimes illustrated guide to how to build almost every aspect of a structure for most types of construction.

A footing or footer is the last part of the building to be designed.  It distributes the load of the building to the soil.  The larger the surface area of the foot the less load is distributed on a section of soil.  A continuous footing is best for most circumstances.  If there are soft patches in the soil or uneven loading (wind, snow, people) it will help absorb that across a wider area preventing sinking or shifting.  The more contact you have from the structure to the soil the more stable.

The illustrations and requirements are even free online laid out in the building code.
http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_4_sec003.htm

[Pine Cone]

Maybe I need to reevaluate my plans.  I have plenty of trees up there and I'd like to use them to reduce the cost of lumber.  Have you ever heard of anyone basically framing a cabin out of logs and then using something like plywood to create the walls?  If I did something like that and made the cabin much lighter do you think I could get away with 4 piers?  I'd like to include a loft too.

I don't know a lot about framing or construction but I'd love to learn.

This cabin is not going to be a permanent residence, it's just a project I've wanted to do since I was a kid so it doesn't have to be perfect.  My biggest concern would be the thing collapsing on me while I was in it.

Bob - Welcome, and check out my building post here http://countryplans.com/smf/index.php?topic=8030.0

I built a 14'x14 foot cabin from logs on a pier foundation.  I used 12 concrete piers for my foundation and could have used more.  I cut some of my logs into 8"x8" posts and built a post and beam building using logs as infill between the posts.  I could have used the same post and beam method and then used plywood to build the bulk of the walls, just like you are suggesting.  I had a friend with a portable sawmill help me turn some of the logs into lumber which was also used to build the cabin. 



I'm not an engineer, but I do know you will need more than 4 piers for an 11'x14' log building.  You need to consider the weight of the logs, the floor, the roof, and add some more weight for possible snow and wind loads.  My calculations led me to believe that 12 piers was about the minimum I needed.  Since then I have added earthquakes to my list of building threats and wonder if 12 piers is enough.

I used ideas from James Mitchell's book "The Craft of Modular Post & Beam: Building log and timber homes affordably" which can be found on Amazon here... http://www.amazon.com/The-Craft-Modular-Post-Beam/dp/0881791318

The book is full of good ideas and options.  You might check to see if your local library has a copy. 

The State of Alaska has a great book on building log cabins which can be downloaded for free from this web site... http://www.ahfc.us/reference/log_construction_manual.cfm

Lots of other good sources of info out there on the web.   If you haven't found them yet, the Log Home Store's website has lots of info and is a great source for stuff you will want to buy if you are building a log home.  http://www.loghomestore.com/

Don't get discouraged by all the good advice you are getting.  It takes a fair amount of effort to actually complete a cabin regardless of how it is built.  You can't skimp on the foundation and expect the rest to work.  Everyone giving you advice has already faced some version of the decisions you are making.   They are all good folks trying to save you money, time and effort in the long run. 

One other option you could consider is to not have a traditional foundation at all. You could build the cabin on pressure-treated beams set on a crushed rock foundation, a building on skids.  I come from a forestry and logging background of lots of old logging camps had cabins built on skids that were moved from place to place.  They might shift some from frost heaving, but at least they won't fall over because a pier failed or sunk into the ground...  I built a small 4x8 shed that way and have seen buildings up to the size you are considering built that way. 

Lots of options out there, but like others have suggested, it's good to have a plan... I made several before I ended up with the one I built.  I even made some scale models to help me figure out what might work for me. 

Good luck, we know you can do it...

[bob57434]

Hi everybody! It's been a little while but here's an update:

I'm going to build post and beam using the timber available on the land.  I've been doing a lot of reading and research and have learned quite a bit this last week.  The new plan is for an 11x20 cabin.  I haven't found a lot of detailed information on pier spacing for pier and beam foundations but I have a feeling the plan I was hoping to use won't work...

I was hoping to use 6 piers total (8" reinforced sonotubes, ranging between 12" and 30" above grade).  So the spacing on the long side of the cabin would be 10' and the spacing on the short side would be 11'.  Then using 8" round posts over each pier and large beams above the posts (perhaps 8x8).  I'm not sure if that post spacing is too wide but I think the pier spacing is probably pushing it.  The walls will be lightweight (plywood).  Maybe I can use extra-large beams to span the 10' gaps?

I was able to rock my previous piers back and forth until they broke... chalk that up to a learning experience.  I really like the post and beam style of building.

Any comments?

As always, thanks for your help.

[bob57434]

Pine Cone - I'll check that book out. So far my favorite is Timber Framing For The Rest Of Us. I've never heard if skids - they sound interesting, I'll check them out.

[alex trent]

In my opinion, 11 feet between the rows of piers is fine. The other way is a bit far. Just put in two more posts and use 8. That gives you 6.5 feet between and is a lot better.

The 8" tubes need to have some extra area at the bottom...the 8" is fine for vertical support (make sure you use rebar columns, not just rebar stuck in). And 8" wood on top is fine too...more than you need.  Be sure to have a good system to attach the posts to the piers...that is the weak link in these systems. Need to really pay attention there.

If you do this, it means your beams can likely be double 2x10s, which are ez to handle..they will have no problem with a 6.5 foot span as your build is now planned. you do need to check that out in the span tables, which unlike the pier/post spacings you had trouble finding are readily available.

[Squirl]

10 ft is generally considered a long span between piers.  It is still close the span distance of 14 feet that you had originally proposed. You are going to have the similar difficulties of weight distribution.

The beam between posts is generally known as a girder or header.  The building code has charts on sizing per span.
http://countryplans.com/smf/index.php?topic=10511.0

These charts of girder sizing are for the even distribution of framing.  Timber framing is a different type of carpentry and construction though.  Maybe an experienced timber framer can help you with that.

[bob57434]

The timber framing I'm considering isn't the traditional mortise and tenon/intricate joint/wooden peg type framing, that's way past my skill level.  I'll be using metal brackets and large screws.  As far as attaching the posts to the piers, this is what I'm planning:  Anchor bolts coming out of the piers to which the sill log (hewed flat on top and bottom) will be bolted.  On top of the sill (or girder?) the post will sit.  I was going to attach these posts to the sill by vertical #4 rebar pins and metal brackets (angle irons).

When you say "rebar columns" do you mean that the rebar needs to span the entire length of the concrete?  That's what I've been doing, using 3 pieces of #3 rebar.  They just stretch straight up, not wired together or anything.

A final issue:

These are the two piers that I was able to push over:



I have no idea how I could have got them out of the ground so I expanded the length of the cabin so they will just sit under the cabin.  The sonotube and 8x8x8 block portions of the piers have been demolished so there is just a big concrete block under the ground left.  So, going from the back to the front of the cabin there are plans for piers at 0', 10', and 20', with concrete masses under the dirt at 14'.  I like Alex's suggestion of using 8 piers with a 6.5' spacing but without removing those old piers at 14' I don't know how I could do that. So...

I was thinking of using 10 piers (5' spacing) instead.  Regular piers at 0', 5', 10', and 20' and then at 14' I would create a new pier using pressure treated 6x6 posts on top of the flat concrete masses that have been left in the ground (one is 2' deep, one is 1.5' deep).  They would be connected to the concrete with metal fasteners drilled into the concrete.  Then supported by PT 2x4's bracing the post from all 4 sides and connected to the edges of the concrete.

If that sounds like it would work I would probably make the piers at the 5' marks out of PT lumber as well for symmetry.

[Squirl]

I will pass along a few pointers, basically parroting what I have read from others with much more experience than I.

Screws are against code for a reason.  When they fail they tend to break instead of bend.

When hanging attachments. More connections are better than one large connection.  It helps distribute the load over a lot of surface area and connections.  When all the load is concentrated on one area of the beam you are more likely to have cracking.

On the current piers.  Sledge hammer, maybe a chisel, and a whole lot of elbow grease should do it.  They also rent demolition chisels at home depot.

[MountainDon]

I'd break up the old piers and maybe cut the rebar off at ground level if you can't get below grade easily. You don't need those reminders around forever.


Note on beams. Someone mentioned handling them.  You don't need to handle built up beams if you build them in place on the piers.

Make sure you know how you are going to brace the piers. It's hard to nail into concrete.

[alex trent]

Sounds like a plan.

1.  Rebar columns...just wire the bars together. Here we use 1/4 inch as "wire" on 3/8 columns or 1/2 inch for two story.  Not just sticking them in the concrete helps keep them positioned..worth the effort.

2.  Piers and posts...I need a bit of clarification to help. I call piers, the concrete part in the ground.  They can end a bit above ground level (mine are 12 inches) or go all the way up to hold a beam (girder) that is some distance above ground level...this is essentially a continuous piece of concrete from below ground to up to where girders are.  Or, like I did, you can put in piers and on top of the piers  join to wood posts (6x6" in my case) and put the girders on top of the wood posts.

Here is a shot of what i did.  Notice the piers and posts on top and then the girders.  You see I go downhill so the post get longer but piers stay the same height..posts get longer. Disregard the back row of piers which have no posts...a different but germane subject.




You talk about a sill on the piers and then posts on that...I think your posts may be part of your frame not the same as mine. Correct?  That means you have no posts like I did...some advantages in that you lose a connection between the pier and post which is always problematic. I do not like the concrete pier look up any distance from the ground....but that is personal.

3. The way you plan to attach the sill sounds good. Get the bolts in deep in the piers and in the pour.

4. Not sure about posts to the sill...someone else will know.. For my taste all that bracket smacket I do not like.

[MountainDon]

Point to remember... the fewer the number of vertical connections in a pier or column the better. That is, IMO, if you must use piers, it is better to have a pier extend from the concrete footer to meet the beam in one continuous unit. Hence my preference for foundation grade PT timber piers or maybe one piece pored concrete piers/columns, but those take a little more effort to get the forms all level and then to figure out the all important and too often neglected bracing. That provides fewer points to fail, to fold, hinge or roll over. But that's me, my opinion.

[alex trent]

I fully agree on one piece piers/posts a la Mtn.Don

Once you get started like I did, it becomes apparent how vulnerable the pier post connection is.  That is why, at almost the last minute, I poured the pack row of piers so we could mount the girder right on them.  The big wind forces will be front to back and this is a bit of a safety check on pushing the thing over.  Here in the back, it has no post connection so has to do the pier.   Not really sure I needed it, but a safety check.

My next place here, which will be smaller and simpler will use 8x8" post sight in the ground to the girder. We have no PT here, but I have some  concoctions i will try. It is also cheaper an simpler. an worst case is that if bugs really eat it up...you can dig them up and pour a concrete pier...or something.

[bob57434]

So a friend of mine told me he built a similar cabin in a similar location to mine doing something much simpler:  He said he just used single 8x16 blocks every few feet and laid a PT 2x10 sill over the blocks and built up from there using typical 2x4 construction.  He says after 15 years it's still pretty level and works fine.

That sure sounds easier than what I've been doing.  Any thoughts?

[MountainDon]

He says after 15 years it's still pretty level and works fine.

Pretty level would annoy me to no end if it was my cabin, but then I pride myself on the ease with which our door opens and closes and the fact that it seals out the drafts when closed. 

What we don't usually hear about is how owner-builder projects perform over the years. Darn near everything can look good in the short term. But that doesn't even follow true; one project that never made it through it's first winter and spring comes to mind.  One of our members has built a shed on a foundation similar to the one your friend built. He has stated he would not do it that way again; but he learned from it and was willing to pass on his impressions.

IMO, if the building is truly a shed, and not a cabin masquerading as a shed, simple skids and blocks sitting on the ground can do the job. The shed I built sits on 6x6 PT skids that rest on single depth concrete blocks dug into the ground. It moves a little with freezes. Not a lot; it's okay for a shed whose door was made loose on purpose to cover any eventual movement. 

My opinion.   I also hate to rebuild or build things twice.