hello,
got a question about piers.
i bought the 20x30 1 storey plans, and want to extend it in length to 36 or 37 feet.
my plan was to auger a 12' dia. hole 36" and chip the bottom 12" out 6 more inches in dia. then 12" sono tube above grade ~ 36"
my soil is thick red clay
my frost depth is 16"
You can extend the beams and add extra piers so long as the spans are no longer than on the foundation plan.
From your information it sounds like you plan the pier go down 36" below grade with another 36" above grade. You want to be below frost (you are) and on as solid a footing as possible. Flaring the soil for a wider footprint is a time proven technique.
Some clays can have problems when the are wet. It would be wise to have an experienced local soil expert or foundation contractor look at what you are getting out of the bottom of the hole and make sure it will hold up your sturdy piers. Otherwise it should work fine.
You're proposing 6' columns that are half buried in heavy clay with the weight of a house on top. Are you sure that when the wind blows on that heavy load and the soil is wet that the columns will not rotate?
Thanks John.
And Don_p, is rotation a common problem? Ive never heard of that?
It would actually be the house that could rotate under very heavy sidewards (wind) pressure. The effect is to move the piers out of vertical and in opposite directions on either end of the beams. This leverage is increased with the height of the pier. Cross bracing (wood posts) can offset this force.
For a one story house in normal soils it would take some pretty extreme earthquake or wind forces to produce the needed push to do this. But, the same advice above applies. The trouble, especially with long duration earthquakes, is that wet clay soils can sometimes "liquefy" - not something you want to experience under your house. :-[
This is considered to be an engineer required foundation type, IIRC they are allowed for small buildings provided the pier is not more than 12" above grade. You're outside those rules of thumb several ways. The inability to reliably transfer wind and earthquake loads from building to earth is the reason this is not a common codebook approved foundation type. Masonry pier and curtain wall foundations and treated wood crawlspace foundations on a gravel trench are approved right out of the book for up to 4'. Horizontal loads travel down the length of either one set or the other of walls and cannot overturn them, where with tall piers it is much easier to tip them over.
Found some pics;
The forces at work on a pier,
(https://i180.photobucket.com/albums/x109/windyhilll/post.jpg)
Section view of a wood crawlspace;
(https://i180.photobucket.com/albums/x109/windyhilll/PTcrawl.jpg)
astidham,
About a year ago I started on my 16x24 house. I went with tall concrete piers like you are planning. I also have a clay soil, and needed to get down 36" with the footings. I rented an mini-excavator and dug two trenches so I would have room to build the footings. (2'x2') Bracing the sono tubes to keep them plumb turned out to be a lot of work. Any way...long story short. I completed one row of piers and the footings for the other row at a cost of almost $2500. This included the lumber for the beams. I would still need to purchase the concrete for the other row of piers, angle iron and brackets for the needed bracing, insulation for the floor, some kind of plumbing enclosure to keep pipes from freezing, and maybe skirting.
I would not build a concrete pier foundation again. The cost of concrete, rebar, and the expensive pier to beam brackets add up. By the time I added in all the other stuff needed for a pier foundation...beams, bracing, floor insulation, skirting, and plumbing enclosure, I was at about the same cost as it would of been to build a concrete block crawlspace (much stronger, and added storage/storm shelter).
I found myself way over budget and behind schedule on the 16x24, so I put it on hold and built a 12x16 to live in while we build the larger house. I went with wooden piers on the 12x16, I used a two man auger to drill the holes for the piers. Going 36" down through clay kicked my ass! d* If I ever do it again, I will rent the one that is mounted on a Bobcat.
The wood piers are much easier to work with, and adding bracing is much simpler than with concrete piers. Yeah the wood won't last as long as concrete, but I needed a low cost foundation, and had already found out that concrete piers aren't really a low cost foundation for me.
Just wanted to let you know that you should really crunch the numbers before you decide on a foundation. If you want to go with something that's going to last a long time, there might be better options than concrete piers.
Thank you Don_p and Beavers.
i think i will get an estimate for a block foundation.
Are you planning on doing all the foundation work yourself, or contracting it out?
At first the concrete piers seem quick and cheap...auger some holes in the ground, drop in the sono tubes, and fill with concrete. It turned out for me to be all the other stuff involved in a pier and beam foundation that drives up the work and costs.
If you are looking to contract out some of the work, maybe you could find someone to excavate and pour the footing, then do the block laying yourself? Doing the footings seemed like the toughest thing for me, getting everything lined up and level.
If you look in the builder gallery Speedfunk, and BishopKnight have both done dry stack blocks. Looks like it's pretty DIY friendly, might be worth checking out.
Good luck with whatever you decide on for a foundation! Just one of the first of many nerve racking decisions when building your own house. ;D
Beavers,
i did plan on doing the foundation myself, but if it is block i might farm it out.
Most homes built on this forum look to be on wood or concrete piers, is a wood post foundation better than a concrete pier?
when i mention wanting to raise my house to ~36" or ~46" Im told its not recommended? but looking through this forum most houses are constructed this way? ???
I'm very confused.
if it would be bad for me why is so many people building this way?
Many small cabins here have been built on wood posts/piers.
Many of us have built using the wood pier and beam system. It does work but in many places won't get approved. Also if not done right (bracing) there is potential for failure under some conditions of water soaked ground, high winds, earthquakes and so forth.
So, #1 question; will there be permits and inspections? If so ask those folks if pier and beam can be approved. If they can be approved the authority figures may advise you what they will want to see. They may not, they are under no legal obligation to advise, only to approve/deny.
If pier and beam can not be approved, or you decide to go with a concrete and block perimeter foundation you can find all the info you need to build one prescriptively by consulting a code like the IRC. Versions are available online for free viewing.
VA https://www2.iccsafe.org/states/Virginia/Residential/Res-Frameset.html (https://www2.iccsafe.org/states/Virginia/Residential/Res-Frameset.html)
Seattle http://www2.iccsafe.org/states/Seattle2006/seattle_residential/res_frameset.htm (http://www2.iccsafe.org/states/Seattle2006/seattle_residential/res_frameset.htm)
Pier and beam can work, but there is no "guaranteed to be approved everywhere, one size fits all" solution to the design. The higher off the ground the more problematic it might be.
Does that help? ???
Thank You MountainDon,
I Need a permit, but no inspections or review of my plans or how Im building.
I have asked the permit office many questions. they cant answer anything just take money for the permit.
I would build on concrete piers, or whatever else i need to that will work, i just have noticed many people building the way I have been told not to in the same state with same soil conditions, and it made me wonder.
I would love a suggestion on what to do.
I was thinking about building 3 rows of 5 piers, 36" deep and 24" above grade.
A concrete guy gave me an estimate for 4700.00 for a perimeter footing anb block to 32". I thought that was a little high.
the footing would have been 18" deep and 16" wide
I've probably added to your confusion here and I'm sorry for that. The trouble is trying to give structural advice about conditions we can only guess about.
The best advice is probably local - what has been working in houses built in your area. Look how the older houses are built (the ones that have lasted).
Here's the deal. 99.99% of the time a house exists all loads are downward. All this talk here is about what might happen with that 100 year event - an earthquake, flood, hurricane, etc. There is a great deal of differences in property and what the exposure is to such events.
Local engineers have numbers for these potential events and will analyze a structure to build in extra strength to resist such forces. This is expensive of course and adds not only the engineering fee but the additional cost of shear walls, hold downs, etc. If you are building a large or expensive house this is a minor expense and valuable insurance. Don_P is able to explain better than I some of these forces that engineers worry about.
However, remember that engineers tend to over design and worry about things that may never happen. That is their job and if you were going to sign your name and affix your stamp on a set of drawings that would be available for lawyers to look at 50 years from now so would you! :-\ There is a strong need to CYA at work here. Inspectors also have the same CYA motivation. Some building departments now require all submitted house plans to be engineered and stamped. This is largely to protect the agency from lawsuits. This doesn't mean the house is now guaranteed to stand up to anything nature can throw at it, only that the responsibility has been shifted to another professional.
What is the best path for the economical building of a small owner-built house we might ask. In the plans I design I try to cover the foundations that will work for most all options and locations. Pier foundations are the ones most subject to special local conditions. The two things that are a potential concern with this project are the clay soil (if it can get sloppy when saturated) and the taller piers. Maybe the soils don't turn soupy where you are. Maybe the winds never get forceful enough to twist the house. Maybe we are just getting worked up about a non-event.
That's what a walk around inspection of local houses of the same general size built in the same soils will tell you. Local wisdom from contractors, builders, farmers or other owner-builders can help put your mind at rest. Remember, you aren't going to be suing yourself and wood frame houses are very forgiving even in those 100 year events. They can pop, sway and sag all without much danger of catastrophic failure.
Thank You John
Good points John!
Around me there are tons of 100 year old huge two story farm houses, all built on red brick foundations with no rebar. I'm sure none of them would even come close to being "up to code" but they are still standing today. A building department would likely laugh at you if submitted plans to build the same house today.
On the other hand I look at some of the mass built subdivision tract houses that are slapped together in a couple of months in the cheapest way possible. I'm sure that they are all stamped by an engineer and every single one of them is built to code, but will any of them still be around in 50 years...100 years? I doubt it. ???
I guess somewhere there is the perfect blend of engineering/code book, and common sense building practices. Thankfully there are still some areas of the country where the owner-builder can decide what the perfect blend of the two is.
I'm with you Beavers, my lil cabin stood on 8 foot tall 4x4's on 8 foot centers, some on stacked river rocks right in Earthquake country...been there 86 years now! My modern homes have all required extensive retrofit to fix sagging, cracking, failing foundations...I'm talking $50,000 puddle pours under/around the perimeter . They drove large diameter steel pipe 30 feet into the clay soil and filled them with concrete, then capped them with a car sized block of concrete. Same as used in the Webster tube (underwater tunnel from Oakland to Alameda)
I notice you all have taken diametrically opposing views and agreed with one another :D
The building codes allow foundations without engineering that have proven themselves adequate for most conditions most of the time. They are detailed in the codebook. One question to ask yourself... Why isn't pier and beam a prescriptive foundation type? The building code requires engineering for methods that have shown that they need to have competent design to avoid failure. This type of foundation has a long history of failure when done poorly. I am biting my tongue.
The requirements are basic, determine the forces to be resisted and build sufficient to resist those forces. Do we have any design guidelines here? Not that I've seen presented. People are trying to develop lateral resistance with the soil... what is the soil strength, minimum embedment and maximum height to resist what load? We haven't a clue. Step back and think, ignore the soil, figure the loads and brace as if it were pinned to a parking lot. I have been attempting to show some ways of doing just that, there are others. Nothing to get worked up about, just do it right. Either put in a prescriptive foundation or have someone competent help look for an alternative.
I just had a design sail through plan review. It shouldn't have. A few emails and I'll be handing an engineer a check for a whopping $250 to review a couple of areas. I didn't have to, it was simply the right thing to do, for one house, just one family, to check my "engineer required" portions... I cannot begin to fathom. A friend of my wife's is one of those new age astrologers, just sort of pulled a title out of air and people seemed to form a line. I've yet to hear of her referring a client to a mental health professional. I suppose it is possible that none of them are nuts.
Scroll down to "pure pier and beam";
http://www.metroleveling.com/fr.pdf
The windup before the pitch in Haiti was 200 years, they had forgotten, and it failed. I've had greater than the engineer's 100 year event hit a house 1 year old. Mother Nature doesn't much care for rules either :).
Don,
Not sure which posts you were referring to...
I just really don't see where engineering is needed for the smaller houses. (12x16, 14x24, maybe even the 20x30)
I also don't understand why ICC can't include the post and beam foundation in the code book. They give pages and pages of charts for everything else, couldn't there be a chart for bracing requirements based on pier height, and type of material? Just seams like it would be easy enough to spell it out and not require engineering.
It's not rocket science or black magic. With a little study and common sense the average person should be able to design a good pier and beam foundation for a small house IMO. You've helped me a ton (Thanks!) to get a pretty good understanding of the forces at work, along with the beam tables, design articles, and all the other info you have pointed me towards I think I've designed a pretty damn good foundation. Is it perfect...no, but I knew going into it what it weakness' were, and weighed the pro's and con's. When the next flood comes through town my house will be high and dry sitting on piers while everyone else will be under water again. If a tornado comes through my house will probably be gone along with most of the other houses in town.
For those of us building with cash, the difference between a wood pier and beam foundation and a full perimeter foundation is huge. I think for that reason alone, people will continue to build pier and beam foundations. I'm still convinced that with experienced people like you around to help educate people and point them in the right direction a safe pier and beam foundation can be built.
Sorry I can't resist a little rant about engineers...
I'm a surveyor and do construction surveying for highways and bridges and get a lot of first hand experience with plans stamped by engineers.
EVERY single project I have been on has had multiple errors in the plans, the same ones that have that nice P.E. stamp in the corner.
For example...
Pipes that make water flow up hill
Paving grades that create launching ramps at intersections
Bridge girders that need a girder stretcher to be able span the piers, because the engineer doesn't know the difference between horizontal and slope distance
Wing walls that crack and fall off of box culverts within 6 months
The list could go on and on...and include all kinds of basic math errors. It would seem that the person who stamps the plans never even bother to double check their work.
I know that just like any profession there are the good and the bad. It seems like a lot of people think that if a PE stamps something it must be safe. Based on my experiences there are some PE's that I wouldn't trust to design my doghouse. I just think that the owner-builder who does their homework should be able to design something just as safe on their own.
BTW- You've been a HUGE help to me Don, and I'm sure to a lot of others on this forum as well! I'm just kind of surprised to see you insisting on engineering, instead of steering people to learn what they need to know and do it themselves. ???
Quote from: Beavers on March 25, 2010, 08:11:56 PM
I just think that the owner-builder who does their homework should be able to design something just as safe on their own.
This is the other Don, and I just want to contribute my 2 cents worth...
The key phrase in the above quote is "does their homework". Some do not. Some guess. We've had examples of that seen here, from a poorly executed pier foundation and "beams" nailed to the sides of posts with expectations that some 16D nails will hold up the entire weight of the structure, and so forth. On the other hand there are also some stoutly constructed cabins.
The other Don, ;D
I see what you are saying, and with a pier and beam foundation the consequences for guessing and winging it could be severe.
If you are building your own house you need to do your homework for everything though. If you don't take the time to figure out your foundation you most likely won't take the time to figure out good framing, or electrical practices. Either one of those done wrong could be just as deadly as a foundation that gives way.
I'm pretty sure that Don_P said that pier and beam used to be covered in the IRC. If they would just include it again it could make it easier for people who don't do all their homework to build a safe house. In most cases it seams that people choose pier and beam based on cost. Has anyone ever had a wood pier and beam foundation stamped by an engineer? Would be interesting to see what the engineer came up with, or if they would even go for wood. ???
If you go with that added expense, seems like it would be easier just to go with something already spelled out in the IRC.
Ummm, Beaver's,
These braced cornered pier designs I've posted... you thinking I came up with that or do you reckon maybe I had a casual conversation after I saw something tip over :).
A good plan with execution that did not fit well with the soil type, the pier height and the lack of effective bracing.
(http://www.prohomesteader.com/countryplans/falling1.jpg)
(http://www.prohomesteader.com/countryplans/falling2.jpg)
I didn't want to embarrass anyone, but there is a lesson here. The problem was partly that the ground became waterlogged and squishy (pardon the technical jargon) and partly due to the lack of bracing coupled with the pier height above ground.
I feel badly that nobody here, including myself, did not emphasize the thought that there was a serious lack of pier bracing before the walls went up let alone the roof installed. I don't want to see something like this repeated.
Those pics are alarming and I feel for the builder/owner...BUT, it does not appear that even steel simpson brackets were used to connect the beams to the piers (not that it would prevent this failure) and from this angle it looks like the piers are 8 feet apart on this evevation? Not Good, but then even for a backyard 6 ft fence I use concrete and steel! On my build with 4x6 PT stilts I used HUGE concrete footings and SERIOUS 4x6 bracing! Even with heavy guage simpson post/cap brackets and HT22's on every stilt, I am still considering more BRACING. Here in Earthquake country, I have done this to all on my conventionally built homes (with perimeter foundations), I braced the short concrete pier/post connections on both sides with simple plywood squares nailed to not only the post but also the floor joists they support. Similarly, I have used simpson ties extensively. I also have "McGivered" some STOUT triangle shaped steel old pallet rack supports mounting them onto the underside of the floor joists and beams, butting them up against the concrete perimiter foundation... it must have worked as that house didnt move while others on my street were thrown off their foundation in the last big quake! I also randomly supported the rafter/trusses in the attic with plywood squares and 2x4 bracing in every direction. Earthquakes teach you things! If you have never been in one, they are ALL POWER, dwarfing ANY forces you are familiar with. Street turn to waves of asphalt!
Beavers,
That was flip, I was working on this post :)
Thanks, I do appreciate the praise.
First off it is the law... I render unto but you can use your judgement. I have posted several options that I think an engineer would approve. The recent series of braced corner drawings from my end are outside of code, they are not full perimeter. They were the result of a conversation about a failure with someone I consider to be competent. If you're going to wing it those ideas are more stable by far then unbraced piers. Should I suggest something outside of what is known to be safe and will pass easily... probably not.
Rather than asking me, who is not competent to perform this work, pool your resources and have a set of basic guidelines drawn up. Engineering students need projects too...
One old credo did pop into my mind in the back and forth "An engineer's job is to do with one dollar what anyone else could do with two." But yes, I could tell some stories ;)
Don, you were posting while I was writing. I read back through that thread at the time, there was warning given, maybe not loudly enough but it was there. Notice all post bracing was assumed to be given by the soil and that unknown was not up to the task. If it is unquantified call it's bracing zero and brace adequately by another means.
This is from an earthquake. Obviously they didn't use any embedment in the ground to try to brace it but it was braced well enough for the posts to remain upright even when it slid off its footings. Notice how the braces oppose each other, are on every pier in both directions and connect low, like the drawing I posted above. I doubt those are just nailed. I've seen other pics from this quake with the houses on the ground and unbraced piers laying around. Those houses just dropped and broke.
(https://i180.photobucket.com/albums/x109/windyhilll/PnBHawaii.jpg)
Don_P...those are great pics of the earthquake damaged home! Wow, even tho the footing failed the simple 2x6 bracing held up! Imagine the forces as it came off the footing! To me the 2x6 braces to not look beefy enuf, I would have used the same dimension lumber as the pier itself, but look how well they did!
It looks like the Hawaiian foundation above had no anchorage to the pier footing other than gravity. With earthquake forces lifting up and then moving the ground (or building) laterally the bouncing house came back down someplace other than the center bearing of the foundation block. :-[
A cast bracket in a poured tube pier could have helped hold the two together.
It could have been much worse without the bracing. Triangles RULE! :D :D :D
Quote from: eddiescabin on March 25, 2010, 11:30:27 PM
Don_P...those are great pics of the earthquake damaged home! Wow, even tho the footing failed the simple 2x6 bracing held up! Imagine the forces as it came off the footing! To me the 2x6 braces to not look beefy enuf, I would have used the same dimension lumber as the pier itself, but look how well they did!
lumber is strong.... minimum specs for a 2X4 in vertical compression to pass grading is 7 tons I believe....
We are planning a 20x32. The location is a rock shelf above the creek on our property. The current plan is to sink pins into the rock and then place concrete piers w/rebar over the pins and extend the pier up to the support beam. We do not plan to elevate the beams on posts. The pier height will be just enough to make up for the slight slope of the rock shelf. We do plan to cross brace from the concrete pier to the beams.
I see a lot of builders putting their cabins high up on the piers, often 2'-3' above grade. Am I missing something here? What would be the reason for elevating the cabin so high? I only want the uphill piers just high enough to keep the beam off of the ground. probably 6" at the most.
Terrain can be a biggie. I'm working with some owner builders on a pier and beam that runs from 8" to 6' pier height above grade.
Took some shots today for a job, 10' elevation change across the footprint
Wow, 10' feet, that's a lot! I can understand the site grade dictating some tall piers. What I don't understand is when all of the piers are at least 2'-3' feet tall. An example is the tilting house in MountainDon's post. I have seen enough of them that I wondered if I was missing something. Sorry if I sound derogatory. Unless I had a steep site, flooding issue or the extra couple of feet 'made' the view I would want the structure close to the ground to reduce the number of stairs and engineering complications.
Sometimes a higher building gets you a better view. Then there is the storage issue - kind of a half basement. In a hot humid climate the extra height can mean better ventilation and a house that is further away from moisture and the creepy crawlies.
Lots of things get factored into what we call "personal preferences". That's why every house turns out to be a custom house whether it started out that way or not.
I am building on exposed Canadian shield. It is quite flat. I would like to use the recommended concrete piers. Do you have any suggestions for such a situation (fastening, mortar?). I could find no such example in the plans.
Are you pouring piers on solid rock? Is that the question?
If so you will find that drilling and setting a pin that gets wired to the rebar of the pier will provide a solid anchorage in most situations. Ask a local foundation contractor who has experience with similar building sites.
Several forum members have built piers this way.
I was wondering if I could still use the pre cast piers by mortaring them to the rock?
The mortar would not make a very secure connection, but for a small building in an area without earthquakes or hurricane force winds something like this would likely work. It would be better to use concrete than mortar - it has better bearing strength.
Best would be a small concrete pier poured over pins epoxied into the rock. Then you have some real protection against a sidewards or uplifting force. Since the rock is dense you don't need much of an area - maybe one 8" or 10" dia. tube would do the trick. Just cut short sections for each pier and cast the bracket in the top.
Design errors similar to the character of those noted in the previous post (Beavers).......relative to heavy construction........ can and do occur even for "engineered" plans of residential construction. I offer the following comments about this topic relative to residential design. I am a professional engineer with 33 years experience.......including a wide range of project types, from railroad bridge design to structural design of houses, including along the ocean.
Although design of basic elements..........such as floor joists, roof rafters, "simple" foundation walls..........can be performed adequately by builders and even homeowners using "standard" tables and other design assistance.........there are many other aspects of proper design that are all-too-often overlooked, ignored, neglected or just performed improperly.........especially when a house has geometry or conditions that are not typical.
Many builders and owners take the position that "good enough" is, well..........good enough for them.............meaning that adherence to minimum requirements of the building code is not necessary. They generally opine that design for the long term.......and conditions with low chance of occurrence....... is not important. This position neglects to consider that..........in all likelihood..........the building will be there long after they have gone.........either because they sell and move or because they move on to "higher ground". The next.......usually unsuspecting...........owner then has a house that is of a quality less than what should be to satisfy code requirements.
I try to break down this key issue to anyone who will listen as follows; ..........When you buy a car (whether new or used), you expect the brakes to meet some safety standard. If you knew.......before buying the car.........that design of the brakes did not meet minimum safety standards..........you would either not buy the car or you would expect a much lower price compared to the usual price for a car with up-to-standard brakes.
Design codes are based on the probability of events ........in the long run........that have low probability of occurrence in the short run. We try to ensure that what happened during Hurricane Andrew (widespread severe damage to buildings all at the same time) does not happen. Much (perhaps the vast majority) of damage that occurred to houses during Hurricane Andrew was the direct result of sub-standard design and construction..........due to those responsible taking the position that building should not have to conform with "overly conservative" requirements of the building code.
Houses are most generally designed by architects, without any input from a structural engineer. From my experience..........the vast majority of architects today do not have adequate training or experience to provide adequate structural design......except for perhaps a small rectangular house far away from hurricane zones.
It is also the case that even licensed engineers can.......and do....still make major design errors for residential construction. However........also based on my experience..........I have seen the aftermath of many major problems with houses that were supposedly "designed" by builders and (to lesser extent) owners themselves. More than a few of these have landed in legal mayhem.
For houses with relatively complex geometry..........proper structural engineering is essential.
The one design area that is least understood.........most neglected...........and most important (outside of serious earthquake territory)..........is design for lateral resistance to resist wind. Seismic is not so much of a problem because it is generally considered "important". Design for wind is very important in hurricane regions.........which includes the entire east coast and Gulf coast.........areas with extensive (and expensive) residential construction. Very often neglected is the understanding that hurricane zones extend inward from the coast line a fair distance.
When hiring an architect or engineer............pay attention to qualifications.........not just the fact of a license.