Hi, I don't have much construction experience and I'm kind of learning as I go.
I'm building an 11x14 log cabin which will be supported by 4 piers. The frost line is 36" so I dug my first hole to 48" and built the pier using cinder blocks. The pier is built out five 8x8 cinder blocks stacked on top of six 8x16 cinder blocks. The 8x16's are stacked 3 high so that the base is 16x16x24. Then the five 8x8 blocks are stacked on top of that which creates a pier that extends 16" above ground. It is reinforced by #4 rebar. I have a pic showing this but I can't figure out how to insert it in the post.
My question is this: I poured the concrete in 2 batches - once for the 16x16x24 base and then once for the 8x8x40 section. They are connected by about 16" of overlapping rebar. The 40" section felt a little wobbly when I left it to dry yesterday, is this going to be structurally sound?
Another question is this: Should I pack down the concrete (Quickrete) really tight (with the handle of a shovel) after I pour it? It seemed to compact a lot so I smashed it down pretty good.
Do my plans look sound?
Thanks! :)
Bob
I am really not clear on what you did and I think a pic is worth a lot here. it is not all that hard to post on the PhotoBucket.
I do not think four piers is enough. For a couple of reasons which I am sure others will cover better than I.
On the piers themselves.
You say cinder blocks, but reference a concrete pour. That confused me...did you use the blocks as a form?
On the two separate pours, concrete does not stick together very well, so all you really have holding this is the overlapping rebar, which in my opinion is not enough..that's why you have a wobble and no real sidewards forces on it yet. You need to use rebar in the piers from the bottom up.
Yes you do have to tamp the concrete down well as you pour..as you go along not just at the end of the pour.
Hi, thanks for your reply. OK, figured out the pics.
This is what the pier looks like before I placed it in the ground (it has an additional 8x8 block on top). I used better cinder blocks than those pictured.
(https://i1159.photobucket.com/albums/p631/bob57434/photo6.jpg)
This is how it looks before I did the second pour.
(https://i1159.photobucket.com/albums/p631/bob57434/photo5.jpg)
How many piers do you think would be enough?
And yes, I used the cinder blocks as a form.
I was thinking of using those 8" cylindrical forms for the next three because I don't really like how this one came out. Any suggestions on the best way to do this? I was thinking maybe something similar to the first pier but using the 8" tube instead of the five 8x8 blocks.
Do you think the pier I've already made will be usable?
Thanks again for the help.
Bob
An additional note on the question of the number of piers that I might need - the cabin will be 11x14 and made of 10 to 12 inch logs.
A few quick notes....
1. You do not need forms on the part of the pier in the ground...the soil does just fine. You can build forms for the above ground part only...BUT
2. You should pour the pier as one...don't pour half and then another half. From the ground up to the top.
3. You need rebar from the base to the top....something like 3 3/8" bars in each pier all tied together with some smaller (1/4") rebar and with some spread out feet at the bottom. Adds a lot to the strength. Without that i do not think you have a satisfactory pier.
The bad news..
I think you need to redo this. There are worse. May hold up and may not. But you will have a lot invested in the place and why start with something that is built on an unsound base. The logs sound heavy..needs more than this. It is not great to redo, but this is not all that much in the scheme of things. Just looks rickety.
I think you need..
Assuming you have decent soll that will support the load of you cabin, and six piers sounds close to not being enough for big logs. So need to check out you soil bearing capacity first. Assume it is 3000 PSF, six piers at one sq. ft is 18,000 lbs total. For your size cabin sound OK. But if 1500, trouble. Then:
1. Six piers. You will find people on here don't even think any pier is good. So good reasons too, so it you do pier it, got to do it right.
2. 12 x12 " poured concrete .
3. Rebar from the bottom. to the top with footers.
4. Minimum 4 feet deep.
5. Figure out how you will attach logs to the piers before you pour. They cannot just sit on top.
I'm not a "log guy" but it does seem to me that with 10-12 inch diameter logs the structure will have considerably more mass than a structure built with conventional stick framing. With that in mind I believe that a pier at each corner is woefully inadequate. The best foundation for a log structure will be similar to the best foundation for a stick built structure; a full perimeter concrete or concrete block wall, resting on a concrete footing that is also full perimeter. That spreads the load out over a larger footprint and pretty much eliminates the potential problems of having any one pier settle more than the others. Like I said, I'm not a log guy, but piers go against the grain for a log structure, IMO.
If frost depth is listed at 36 inches the bottom of the footer should be at or slightly below that level.
Thanks Alex and Don for the replies.
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.
Quote from: bob57434 on April 25, 2012, 01:39:32 AM
Thanks Alex and Don for the replies.
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.
My biggest concern would be the thing collapsing on me while I was in it.
I, like you Bob are still learning, Alex and Don have given you sound opinions, and advice. they both have builds listed on this forum loaded with pic's, and Alex's build has helpful video's as well, their foundations were dug by hand like yours and are both nicely done.
Trust them please, you dont want to "get away with" anything concerning your foundation.
It's probably NOT going to collapse on you, but may indeed shift or sink and make your dwelling uninhabitable.
Please keep us updated on your project, every build, and question posed is a chance for us ALL to learn something.
The old log houses here were typically built on 4 piers, under the hard bearing points of the stacked corners. Remember, load goes to stiffness, these are criss crossed stacks of horizontal beams that form load bearing "columns" in the corners. In an old chink style log house, the logs are beams spanning from corner notch to corner notch. The load on each horizontal log (think beam) is transferred to the corners and then vertically down the corner to the pier. I've never seen one of those that hasn't settled but the understanding and ability to build a good foundation was not there yet. Many were later underpinned with brick or dry stacked stone. I've worked on a couple of those where the unloaded underpinning had collapsed and the bearing was back to the original 4 points. So was it done, yes. The weaknesses are settlement and possible lateral movement. These old pier buildings were almost always at ground level on one side to provide some lateral resistance, an anchor against racking. Which worked somewhat until rot releases that connection.
I've gone back under several of these with a full perimeter wall on footings below frost depth. Then to transfer the loads more uniformly down through the walls to the foundation I installed blocking inside the chink joints in vertical "columns" along the length of the wall and beside any openings. That works well on old fully cured logs, with green logs the corners are settling as they shrink and those columns of blocking can hold things up. The slower you work after getting the roof on the more time you have to tune this in as things dry.
The sill logs which carry the floor and pass under the door openings is then a very critical beam. It carries all the accumulated weight from above up to the header row of logs over the tops of the windows and doors where you again have full length spanning logs from corner to corner. The weight is again transferred to the corners for all loads above by those header logs. All loads are carried on those 4 corners.
The issuse in my mind are the load bearing capacity of the soil, you need a broad enough footprint so that the piers do not sink. The piers need to be wide enough to be stable and avoid overturning. My feeling is that building corners that run 4' in each direction out of each corner would provide that stability and bearing area. That approach really calls for an engineer just as independent piers do. It did come from tailgate conversation with an engineer. I have no problem with any type of construction if done right. Alternative methods can be tougher to get right. Because of that many people wing it. That's where we get into trouble, the things that we either don't know or that we do know that just ain't so.
The floors in those old cabins was often independent of the walls. The floor or wall logs could be relevelled independently of one another. A neat idea but a mighty poor diaphragm to reinforce the base of the walls.
The log house here was basically a horizontal framing system. The cabin could be hewed out relatively quickly, chinked and occupied. As time and funds allowed vertical furring strips were applied to the logs inside and out. White clapboards were fastened to the furring outside, lath and plaster to the inside... you had now arrived and hidden your humble roots. Some folks "made it" and others remained in the old chinked cabin. The ones that usually survive here are the ones that were weatherboarded. The flat hewn faces facilitated applying furring strips although the logs were later hewn at those locations until all the strips on a wall planed in flat. The original hewing also produced logs that were slightly tapered narrower at the top than at the bottom, they were hewing a tapered clapboard type drip edge in the log.
On the weight of logs, remember the prescriptive codes include solid masonry structures. We've got up to 16" thick x 10' tall prescriptive stone walls under part of the current house and a chimney that goes about 50,000 lbs and is only 18 square feet at the base. That chimney would put close to 3000 pounds per square foot on the soil, it would likely sink. We put a 40 sqaure foot footing under it and got the load on the soil down to about 1250 lbs per square foot, (less than 10psi if that helps in thinking about it). Now the soil can bear the weight without the chimney settling. Getting that snowshoe, the spread footing, right for the soil underneath the load is what prevents it from sinking. In the case of the heavy chimney it probably makes it easy to visualize that the spread footing also needs to be thick and well reinforced enough not to allow the chimney to "punch through" the footing. A wall or pier on a spread footing needs to think about the same thing.
Concrete does not stick to other concrete well. That is probably why it is "wobbly".
There are a few ways people get it to stick to each other.
Mortar. Mortar sticks well to formed concrete. That's its job, connecting concrete blocks.
Key way. The joint between a concrete wall and the footing is done through a keyway. The provides a mechanical joint, even though the concrete doesn't stick well. It forms like a tongue and groove. This is usually done by dragging a 2x4 through the footing before it hardens.
Concrete bonding adhesive. This is a special type of glue to join two different pours of concrete. Pretty cheap too.
Considering you are thinking a very heavy structure on a very tiny number of posts. I would be especially worried about lateral forces and a wobbly base.
I would start over and mortar the blocks before filling them with concrete, put a keyway between the two pours and use concrete bonding adheasive ($6 at Lowes).
(http://countryplans.com/foundation/img2.gif)
Thanks everyone for your detailed replies.
A few more questions I'm hoping people can answer:
1. I found this website from an article that contained the picture in Squirl's post. That picture made me think maybe the pier I already made was okay because it shows a "concrete or crushed rock footing". Wouldn't using crushed rock be similar to pouring two different batches of concrete since they wouldn't be one solid piece?
2. If I were going to build a concrete or block wall around the perimeter as MountainDon suggested, how would I go about that? There is a lot of semi-crumbly, large-grain sandstone on the property; could I use some of that in the wall to reduce the amount of concrete I need?
3. The soil I am building on is a very solid clay, how can I find out the soil bearing capacity?
4. I read that "interior piers" don't need to be buried beneath the frost line. Is this true? Why?
5. I was planning on attaching the logs to the pier by means of a 12-18" piece of rebar that extends up out the pier. I was going to drill a 1/2" hole in the end of each log and slip the rebar up through it. Any thoughts?
6. Just to clarify, do I want to tamp down the Quickrete as hard as I can when I pour it?
7. And the question I'm most interested in is this - could I build this cabin using logs to "frame" it and then nailing plywood up? I researched timber framing last night and that's similar to what I'm thinking but not exactly. I'm thinking four 12" logs to create the base (the sill I believe it's called) and then maybe every 3' to 4' using a 4" to 6" vertical log as a "stud", probably connected to the sill and header by a mortise and tenon joint and some nails. I'd probably have to hew the logs at least a little bit to nail the plywood to it? Does this sound stable? Could the 4 piers support this structure? It seems like a lot less work that doing a full log cabin.
Thanks again everyone!
Bob
This does not answer all of what you ask, but I am sure others will. Lots of good info to be had and I would say do not get discouraged from the first barrage of comments. I found that it's good to stay ahead of the curve and ask as you plan so you have all the opinions and can choose. As you see already, few things are cut and dried...even though there is tons of stuff written and mountains of code books. I likely could not have built my place without the advice...at least not as quickly and as well. But, you will also find a lot of chaff in with the wheat...so read it all and research some on your own and don't do or not do anything based on one input.
On the piers and the pic you saw. I saw the same one and had a bit of the same experience as you, only I had not started building yet. There are lots of variable in that discrepancy in what you are hearing and what you saw. I think in your case it is mostly the number of piers (likely way too few to support your house from swaying or falling down) Some is also the supporting properties of the soil. Those are both fairly easy to resolve. As you see, piers are regarded by some as not a good option at all. But, those same guys have great advice on how to do it, so if they do not talk you out of it you can do it and they will help you. I built on piers because of the slope of the ground mostly. In your case, i guess I would say if you don't have to maybe you should consider a continous foundation. A log house seems to fit on one better than on piers....asthetically speaking and it sure save a lot of potential problems.
On pouring concrete in two pours....as has been pointed out, there are ways to help compensate for doing that, but the best way to not have to use those workarounds is not to pour them separately. No amount of mortar or additive alone will make it as good as a single pour The biggest thing to point out here is that you cannot rely on mortar between the concrete block "forms" to do any of that structural holding. All that mortar does is stick the blocks together it will not in any way strengthen the concrete inside or do very much to make up for two pours. If you are going to get into all he other things you can do to structurally lock them together, you may as well use a proper form or just pour it all at once. This is not a complicated pier, but you can make it one.
1. It depends on the weight/amount of piers. None of the plans sold for that kind of pier call for 4 piers on a log cabin or are loaded at even a portion of the weight you have proposed. Also, even for the lightest structures, I wouldn't call the gravel with 8" base an overly stable design.
2. Dig. 36" all around. 12" wide minimum solid footing. Blocks with mortar or surface bonding cement. The more points you load the more soil you distribute the load of the house. There are many books on about a dozen different foundation designs and all are written into the building code. If cost is an issue, you can always do the old time way of rocks and mortar, called rubble stone foundations.
(http://chestofbooks.com/architecture/Building-Construction-V2/images/Stone-Rubble-Foundation-Walls-40.jpg)
3. Clay is the usually lowest bearing and heaviest soil. Conservative estimates are 1500 - 2000 psf. Most counties will do soil testing.
4. Interior posts aren't required to be buried only on full continuous perimeter foundations. This is because the purpose to bury them is to protect them from frost heave. With a full perimeter foundation, if properly constructed, should not have moisture in the center of the building to freeze and heave the center posts .
5. For longevity the wood in contact with concrete should be pressure treated or have some type of barrier.
6. Concrete is not compressible. If it is going down when you tamp it, you are getting huge air bubbles and voids in your pour.
7. Timber framing is another ball of wax. It is more complicated than a log cabin, but uses less timber. Don_P is an expert carpenter in the area. Witlock built a really nice one two. This takes a lot more research and reading. I have read 2-3 books on the subject and still couldn't do it myself.
http://countryplans.com/smf/index.php?topic=5331.0
I disagree about the mortar. Mortar has a compressive strength of 1200 psi and a shear strenght of around 100 psi. It is not a large amount, but on a full block wall it is more than enough shear force for structural purposes and is to code without poured concrete. Most concrete block walls are typically connected to the footings through mortar alone.
Concrete bonding adhesive has a higher PSI shear rating (1250) than concrete alone. How that translates into real world applications I can't testify too, but it is rated just as good as solid pour.
http://www.quikrete.com/PDFs/DATA_SHEET-Concrete%20Bonding%20Adhesive%209902.pdf
Looks like I'm the slow typist, well anyway two more cents.
and on the mortar, yes it has some compressive strength, about 1/3 that of concrete... but if lateral is our concern, and I think that is really what your guts are talking about, concrete has very poor tensile strength. Those rebar cages around the insides of big columns, that takes the tension load as a masonry column tries to bend.
1) The pier shown whether on a concrete or crushed rock footing is capable of supporting vertical load. If the footprint is 16"x16" (1.77 SF) and the soil has a bearing capacity of 2000 pounds per square foot...1.77 x 2000 = 3540 lbs. That probably isn't a big enough footprint when we figure for the vertical loads, the building, occupancy and snow.
If you made the pier wobble you instinctively tested the force that most concerns me with piers, lateral. You pushed on it sideways. And you are quite correctly intuitively concerned, wind, seismic, and boys are the horizontal loads. This foundation isn't up to resisting much in the way of lateral forces. It'll tip over.
But I'll backfill and tamp around the pier up to grade and that will resist the lateral forces. Don't look at the height of the pier while thinking that, look all the way up to the top of the sail on that lever arm. If you experience significant lateral load, there is a pretty good likelyhood that isn't going to resist it.
2) There are links to the building codes in the references and child boards, the foundation chapter is the best place to start getting advice about foundations. Typically, dig a trench footing wide, install rebar under the wall location and above the soil and pour a continuous strip footing about 8" thick x 16" wide for most small structures. The top of the footing is level with protruding rebar sticking up periodically along the wall line, block is coursed on top of that. The rebar is tied to anchor bolts protruding from the top of the wall (allthread perhaps in your situation) and those cells along with the wall top are grouted.
3)Web Soil Survey is a good resource about the soil on your land if you are in the database and/or the tables in the foundation chapter.
4) I cannot find a cite for that. A codebook foundation is an enclosed structure, an interior pier would not have moisture under it or extreme cold. I put them all down to frost depth. If you have 4 corners there are no interior piers and the wind is singing underfoot.
5) In reality yes, but we have to prove nobody can beam it up to the mother ship, that's why I mentioned allthread. In high wind areas I've run allthread and couplings from foundation to wall top with a 3" washer and nut up top.
6) As dry as you can stand it and as hard as you can pound it makes the strongest concrete. Excess water creates voids, vibrating or pounding it removes voids making a denser, stronger mix.
Ahh, vertical log construction, find Pinecone's thread. Yes your idea will work, it probably needs more kicking around to get to sizes and such. This is loading the sill at points along it rather than the four corners I described at such unneccesary length above ::). I'd prefer a perimeter foundation but if not more piers will share the load. I'd look into an alaskan lumbermill to flatten one face of the logs although a broadaxe would do the job.
You may find this helpful if you chose to build a block wall or for the rest of your piers if you chose that way.
[embed=425,349]http://www.youtube.com/watch?v=0S864aMMiKA[/embed]
Most concrete block walls are typically connected to the footings through mortar alone.
That is a different situation than a column and it is downright dangerous to transpose the logic to construction of a column or a cold pour. In a wall that sits on a footing, the mortar to the footing is not holding much, no matter how strong it is. The wall is holding up the wall. You won't see many 20 foot high 40 foot wide concrete block walls held together with just mortar. You'll likely see poured concrete columns up and down with rebar. Down here, even the poor people build with a horizontal column no higher than eight feet up tied into vertical columns which are tied into the footing with rebar.
Quote from: alextrent on April 25, 2012, 05:22:04 PM
Most concrete block walls are typically connected to the footings through mortar alone.
That is a different situation than a column and it is downright dangerous to transpose the logic to construction of a column or a cold pour.
Um that is probably why I said block walls and not columns. I was using it as an example that mortar adds strength between cold joints, and does more than just "sticking the blocks together." True rebar adds strength too and I never said not to use it. To say that mortar adds no shear strength at a joint is what I disagreed with. Columns are poured separate from footings all the time in concrete work. They are usually connected with rebar and a concrete bonding adhesive to make a complete joint, which is even better than just mortar (as I also suggested to do). There are three ways block columns are usually connected to footings. I suggested all three. I even posted an example.
I don't know what that has to do with poor people.
Thanks everyone.
Another question: With that first pier I built, could I have just filled the bottom on the hole with stones and concrete instead of using the six 8x16 blocks? Maybe have fitted the stones around one (or more) pieces of rebar that stretched from the bottom of the hole to the top of the pier?
Squirl..
Let me, as a relatively new user who has mined this site for a lot of useful info, and has had to sort out a bunch of junk from the good stuff, find unhelpful about your most recent post and something which I think detracts from the information sharing process. I offer this to you in the spirt of an observation that may help you make better use of your talents and knowledge. This thread is getting sidetracked with this, so this is my last post on this, even though I am sure you will have a lot to say.
The discussion was (and is about columns). You made it about something else to prove a point about mortar on which you are generally correct, but which has nothing directly to do with the subject at hand. Point one: it's good to stay on point and answer the question at hand....
The point of a post should be to help the readers,especially the originator, not to show how much you know or that you were really "right". Point two: More importantly, what you wrote could be easily misunderstood by someone and that would be potentially harmful. When I spoke of the fact that using mortar to fix a cold joint in a column it has nothing to do with the fact that mortar is useful in other situations..like walls. No one disputed the fact that mortar has shear strength and binds concrete blocks together and can be enhanced by an additive because that was not even the subject. But what was said is true about columns. Now you are talking about concrete walls and we are in a log cabin discussion. My rebuttal to your "mortar facts" post was simply to reiterate the point that what you said was not true about the original question, as I found that important point lost in your post about how useful mortar is in which you give examples of walls to prove your point.
The point that was lost on you about "poor people" is that even they, who have limited resources and as such often cut corners, build in the fashion I described because it is so vital. Sorry for the analogy, which missed the point. I guess you are not the only one who does not write clearly.
Let's move on.
The footing if thick enough to develop a solid mass can contain large rocks. I've filled a pier hole to grade with concrete and solid stones as an extender. Rubblestone would cover it, greater than 16". I wouldn't use anything crumbly, that would then control the compressive strength, they should be harder than concrete. You still aren't picking up anything to brace the posts from tipping.
These are rubblestone piers, the singles are 20x20". Under all that is a continuous footing. Since concrete is cheaper than the stone mason we poured the 2' wide footings from frost depth to almost grade. To economize we did drop in rock after we got above the lower rebar. I would put the building on a wall, just as under the porch. That isn't going to tip over and provides a bigger footprint.
(https://i180.photobucket.com/albums/x109/windyhilll/chimney005opt.jpg)
But, you're ahead of yourself. To figure out how to hold the building up, you need to know a lot more about the building. The better the plan the less wasted time and money.
Quote from: alextrent on April 26, 2012, 06:15:27 AM
The discussion was (and is about columns).
Sorry, certain things lead me to believe the topic had shifted to include better foundation options.
Quote from: bob57434 on April 25, 2012, 11:12:59 AM
2. If I were going to build a concrete or block wall around the perimeter as MountainDon suggested, how would I go about that? There is a lot of semi-crumbly, large-grain sandstone on the property; could I use some of that in the wall to reduce the amount of concrete I need?
Hence the videos and discussions about block walls. Sorry for the thread drift.
Again, I appreciate the time everyone's spent helping me out.
So I'm probably being hasty but I built the second pier today. This cabin is kind of an experiment and a learning experience for me, actually if I hadn't screwed up the first pier I wouldn't have sought help on this forum and received all this good advice. Since it's as much about the experience I'll gain building it as it is about the result I don't mind trying out different building techniques and getting a funky result (e.g. multiple types of piers or maybe a wall that only extends along one side of the cabin).
I got up there and examined my first pier - it wobbles about a half inch in either direction. The rebar that pokes out of the top seems to be secured to the bottom of the pier though because it stays in place and kind of pulls down into the pier as the top rocks back and forth (if that makes sense).
I think the second pier I built today is better but I'm not 100% sure it is all good. I've read posts that seem to say that you can put the bottom of the footing at the frost line, my frost line is 36" and my hole is 40" deep. I used three crisscrossed cinder blocks (see pic) and surrounded them with concrete, filling the rest of the hole up to 24". The footer is 18"x14" and 24" high. I used 3/16 rebar this time - two 6 foot lengths running from the very bottom to the very top and two 4 foot lengths overlapping in the middle. The rest of the pier was made with an 8" sona tube. As I was filling the tube and packing down the concrete, the rebar got pushed out towards the edges (see second pic), at the bottom of the tube they are more centered. I will cut the ends of the rebar off when the concrete dries. I stuck a 9.5" long, 0.5" L-shaped bolt five inches into the top of the pier to bolt the first log on.
My main concern is again about the connection between the pier (the 8" tube) and the footer. The tube rests on top of the 3 crisscrossed cinder blocks (the footer) and it seems like most of the surface the tube is resting on is cinder block instead of the wet concrete in the voids of the block (the top block is one of those that has 3 thin openings instead of 2 square openings). Make sense? I'm assuming that that is not as strong as if it were sitting entirely on wet concrete. I lifted the tube up a little to widen the base and packed the concrete with a shovel handle down the tube (didn't know if that was a good idea). Then when the tube was half full, I tilted it a bit to make it level; this seemed to make a void and I was able to pack down the concrete quit a bit after moving it.
(https://i1159.photobucket.com/albums/p631/bob57434/photo2.jpg)
(https://i1159.photobucket.com/albums/p631/bob57434/photo11.jpg)
(https://i1159.photobucket.com/albums/p631/bob57434/photo10.jpg)
So here are some of my questions (lots of them but mostly simple ones):
1. If the other 5 of my piers are solid do you think there is any way I can get away with leaving the first one the way it is? I imagine it has plenty of compressive strength, just no resistance to lateral movement.
2. If my frost depth is 36", is a 40" hole sufficient?
3. What exactly is the definition of a "footer"?
4. Do I just peel off the sona tube down to ground level?
5. Is it bad that the rebar is pushed out to the edge of the sona tube at the top?
6. I only used enough water to give the concrete a kind of gravely texture - more solid than liquid, is this okay?
7. Are my pier and footer attached well enough? Should I push on it real hard after it dries to see if it budges?
8. Is it correct to call the 8" cylindrical part the "pier" and the 14x18x24 part the "footer"?
9. It started to rain so filled the whole back up with dirt before the concrete was dry, is that okay?
Thanks again everyone!
I'll post again soon with a kind of revised plan for the cabin. I don't think I'm doing all logs now - too much work and apparently too heavy. I'm thinking a combination of logs and plywood.
I cannot figure out why you are using the blocks with the tube on the top. Or for that matter the blocks at all.
Why not just use a tube all the way to the bottom of the hole? That would solve a lot of concerns you are having and problems you have.
If it is because the tube is not enough area (which is a good concern), you can pour right in the hole with the rebar in position...lots of ways to hold it....if that is what the blocks are for you do not need them...the hole will hold it all just fine. Put the tube on top of the hole before you pour and pour the whole thing at once. You can just use 3-4 pieces of rebar this way...bottom of hole to top of tube and don't ned any extra pieces in a single pour.
Quick answers (my version) to your specific questions:
1 Judgement call...IMO, no.
2 ?
3. Depends on what you are referencing... in your case it is the first building element that contacts the soil..other foundation elemenets rest on it.
4. I guess...never used them.
5 Yes.
6. Yes less water is better...up to a point and I bet you are on the safe side of the point.
7 Yes, push it hard. However hard you can push will not be hard enough to prove anything if it does not move ..unless it moves and then you will definitely know it is bad.
8. Close enough..if you had a base under your blocks, that would be the footer. Your blocks look more like a pier than a footer to me.
9. OK to me..others know more about curing stuff.
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
(http://www.diychatroom.com/members/arky217-86953/albums/all-pictures/5437-1-18-12-031-600-x-450.jpg)
Nice work! Looks solid and well braced. Bolts with washers are good way to make those connections.
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...
Arky - I like that. What is a chainsaw mill?
From the original post....
Quote from: bob57434 on April 24, 2012, 04:03:45 PM
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.
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.
That sounds smart - lol I might not have much of a choice, I think I broke my wrist at work today. d*
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.
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?
A pier is the base for everything else. I don't like the idea of applying band aids there.
And the band aids you propose sound lousy anyway. And likely more trouble than they are worth.
Quote from: bob57434 on April 27, 2012, 02:15:20 AM
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
Quote from: bob57434 on April 25, 2012, 07:45:12 AM
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 (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.
(https://i753.photobucket.com/albums/xx172/Pine_Cone/Cabin_From_NE_LaborDay.jpg)
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 (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 (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/ (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...
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.
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.
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.
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.
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:
(https://i1159.photobucket.com/albums/p631/bob57434/photo12.jpg)
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.
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.
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.
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.
(https://i1185.photobucket.com/albums/z354/alextrent/House%20Uploads1/Beams2.jpg)
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.
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.
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.
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?
QuoteHe 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.
Quote from: bob57434 on May 07, 2012, 09:31:07 PM
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?
It depends on how you look at it. So he spent a few thousand dollars and weeks of time on something that he is going to spend years of his life in and he cut a few corners to save maybe a few hundred dollars and a few days of work, for it to have a shortened life span and less quality and comfort.
More posts would help solve the balance issue, but there is no solid contact with the ground. 8x16 blocks are usually hollow and without them being filled or a concrete pad underneath it does not distribute the weight over that much surface area of the soil. The lack of a beam between the blocks is a red flag to me.
I don't know the member that Don is referring too, but I am in the same boat. I built something like that. It shifted. It is drafty. It will not last a lifetime. It is a shed.
Why spend all that time and money building a structure to skip the foundation?
Yeah, I agree. I'll only be spending a few weeks a year there but I want it to be nice and to last a while. Two more quick things:
1. I've seen it recommended that I put a layer of gravel down on top of the clay before I pour concrete, is this necessary?
2. I have what I think is a better idea of making those first piers work. I've knocked the top section off so that there is basically a 2'x2'x2' block of concrete sitting 2' under the ground (from a depth of 2' to 4'). I could just pour a new pier on top of that. The top of the pier needs to rise out of the ground 2', so I could pour a 2'x2'x1' foundation and then have 3' of 8"sonotube rising out of that, all in one pour. Kind of like pouring a pier on top of bedrock. Then instead of 10 piers like i was thinking last time I could have 8. They would be 2 rows (11' apart) at distances 0', 7', 14' and 20'. Does that sound doable?
Thanks again guys.
Bob