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Attaching roundwood posts to poured foundation piers  RSS feed

 
Jeremy Droplet
Posts: 25
Location: Central Maine (Zone 4b)
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I'm in the brainstorming phase for a small workshop building I'd like to get off the ground this spring. At the moment I'm thinning out a grove of eastern hemlock and have a number of specimens suitable for use in pole-type construction. However, I have no interest in burying the poles below grade as most books on the subject seem to suggest (probably for cost reasons). I'd like to simply attach the poles to poured footers instead. Searching around the internet shows lots of options, but I'd rather not have to buy any sort of specialty brackets or standoffs or do any extensive joinery on the poles themselves. I'm also trying to keep the purchased materials to an absolute minimum on the project.

Looking at the relevant page on the simpson strong-tie website (http://www.strongtie.com/products/highwind/PostColumnBases.html?source=highwindnav), I see they have standoff bases that are code approved in most situations. This looks like it should do the trick -


Is epoxy really enough to bed the threaded rod into the pole? If this is true, can I simply skip the kit and bed the threaded rod (or rebar?) deep into the pier, and use some doubled up 6mm rubber matting to act as a standoff and moisture barrier? These are materials I have on hand and I really like the idea of not giving any more money to the lumber yards.

 
Jay C. White Cloud
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I have no interest in burying the poles below grade as most books on the subject seem to suggest (probably for cost reasons).


Cost may be for some of the reason, yet the actual savings are marginal in the long run for many that do this, at best. Post in ground is the "original form." Humans have been (still are) facilitating timber architecture this way since the very beginning, and if done traditionally (and well) can last over 100 years. Then, some of these more ancient forms where simply "wedged and fulcrumed" up and set onto stone plinths to continue to serve for several hundred (or thousand) more years.

I'd like to simply attach the poles to poured footers instead.


Actually a very modern practice, and one that is only reflected as having any marginal value in coastal or plains high wind area with great uplift wind events. Even then the "value" is marginal...as the real world actuality of events from a "direct hit" by most major wind events (i.e tornado, tsunami, etc) is going to tear most architecture apart (starting at the roof) no matter what is done...that is just the nature of..."nature." Most vernacular forms look to other means of salvation, from "tie downs" to mass and flexibility in design.

"...I'd rather not have to buy any sort of specialty brackets or standoffs or do any extensive joinery on the poles themselves...."


Sorry for sounding "cheeky" but that is like saying I want to, "...eat cake, but not crack any eggs..." or "...go swimming and not get wet..."

I'm also trying to keep the purchased materials to an absolute minimum on the project.


Now that is very achievable, as our forebears have done this for millenia. The structure will have to be built the way they did it to achieve that...

Is epoxy really enough to bed the threaded rod into the pole?


Yes, if going with a newer method of post attachment. Epoxies (if don't correctly) are extremely strong, often way stronger the OPC and even some stone.

If this is true, can I simply skip the kit and bed the threaded rod (or rebar?) deep into the pier, and use some doubled up 6mm rubber matting to act as a standoff and moisture barrier?


Yes the rod can be bedded in the cement. This is a standard practice yet also has a mechanical "hook" on the end of the rod that goes around the rebar in the concrete pier. Those that suggest embedding rod without this mechanical structuring interstitially in the post are ill advised. To meet uplift protocol spec. and all the directions I have had to address on such projects from the PE.

The rubber pad is definitely not something I would recommend to anyone. This is not only a "condensing surface" it can also very effectively trap moisture, which is going to be an issue anyway as this project seem destine to use OPC...and...OPC is a moisture sponge and one of the worst things to have near or in contact with wood.

I really like the idea of not giving any more money to the lumber yards.


Then I would recommend doing it the way it has been done for thousands of years..."stone plinth and/or post" (best method) or "direct burial" (serviceable method.) Or, if OPC is going to be the choice I am forced to use as illustrated below, I would use small stones to separate the wood from the concrete pier (reinforces with fiber and rebar) to creat the "air space" between the wood and the OPC pierre.

Good Luck with your project!

j

Recommend Reading:

Scribing Post To Stone


Dong style traditional architecture from Southern China, one of the oldest sustained traditions in the world. Simply wood, stone and brick sitting on a stone plinth foundation.


Side view of one of the older structures in a village.


New blending with the old...


This village was known for their chile farming...


New construction (old methods) on the side of a river...


Under construction...


Old frame moved and getting new siding...


Simple stone and timber structure on gravel by Dan Snow...


An example of "raised bracketing" as suggested (but nut needed) in this post thread. My friend was forced by the client and PE to use these and latter alter, then cover them with more cut in stone. All and all...a pain in the "A_ _" to say the least. This frame out of white oak was so massive that nothing really was needed at all but the stone plinths...


Another "OPC pier" project that the client and architect could not agree on. The choice was finally made to back fill with gravel and cap with stone plinths...a suitable compromise.


Frame going up onto foundation...


Finished frame...


Shelter under construction on the Appalachian Trail that sits on stone plinth...


Finished frame with Japanese style entry steps...


Wedding Arch on stone plinth...these have a through locking bolt drift pins to lock them down to large wood plates under the ground for easy transport and assembly.


Close up of contemporary stone plinth foundation in the Asian styling of Southern China...


Completed frame...


Fair Oaks Pool Pavillion Project, Virginia. This shows the complete frame schematic with reinforced concrete with rebar and fiber cement that the county PE and ours agreed to. As a compromise, the posts sit on granite plinth stones with locking through bolts.


300 plus year old stone plinth under a Japanese Minka...


over 200 year old Minka...


Same as above...


What do they sit on for all these centuries? Raised Earth foundations and stone plinth...Take note...this is an area of Japan that has seen hundreds of earth quake on a regular basis...


Another view of same...
 
Bill Bradbury
pollinator
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Location: Richmond, Utah
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It's a shame that I can only give one thumbs up, that was a tour de force even for you Jay!
 
Patrick Mann
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Location: Seattle, WA, USA
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Alpine villagers also have used stone plinths for a long time. Only gravity to hold down the posts.


 
Jay C. White Cloud
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Hi Patrick,

That style is an excellent (and extreme) example!

If you like those, and there are countless forms all around the globe, you probably would enjoy reading and looking at Hórreo. Hórreo are probably one of the finest styles I have studied and a keen example of what "just gravity" can do for architecture!

Regards,

j
 
Jeremy Droplet
Posts: 25
Location: Central Maine (Zone 4b)
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Jay, thanks for the excellent post.

There seems some contradiction though. You mention needing the threaded rod needing to be bent like an anchor bolt around the rebar to have real benefit in preventing uplift, but are content with gravity alone being enough for a stable structure.

I'm not in a high wind zone, and a moderate seismic activity zone at best. Is gravity alone enough? I think it's pretty unlikely a wind event could knock the structure out of its boots, but I could see even a modest earthquake being enough to rack the structure free if not attached. Keep in mind this is not a "timber frame" so to speak, but more along the lines of a pole barn with girts spanning independently supported poles.

The thought of using the rubber membrane is to stop the wicking of moisture up into the wood. Would it not be successful in doing so? I use 6mil EPDM to do the same thing in preventing moisture from entering the straw wall. I would assume it would work the same way here.
 
Jay C. White Cloud
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Hi Jeremy,

There seems some contradiction though. You mention needing the threaded rod needing to be bent like an anchor bolt around the rebar to have real benefit in preventing uplift, but are content with gravity alone being enough for a stable structure.


Well perhaps I didn't (I thought I did) make it clear that I often do not have control over clients, (Permies posters ) and municipal inspectors beliefs. Even my own P.E. seldom sees a reason for these accept in open architecture like a pavillion in an open field or on a beach.

I think I gave a rather healthy portion of examples of architecture that only sit on their foundations...I can give many more if need be...

I'm not in a high wind zone, and a moderate seismic activity zone at best. Is gravity alone enough?


Go back through the list above...focus on Japan...the place with lots of earthquakes and Tsunami...and let me know what your "second thoughts" on this subject might be. It does depend on design and approach, I would agree, yet in most cases, Yes, the weight is more than enough.

I think it's pretty unlikely a wind event could knock the structure out of its boots, but I could see even a modest earthquake being enough to rack the structure free if not attached. Keep in mind this is not a "timber frame" so to speak, but more along the lines of a pole barn with girts spanning independently supported poles.


It will all depend how far you deviated from traditional designs on whether a modern pole building design will work as I have described. I find many "pole structures" poorly designed and underbuilt where there could be more effort placed on good joinery, and less emphasis placed on "how fast can I build this" or "...use more nails...that will fix it." A little more time, and very simple tools plus virtually no bought materials other than roofing and the wood siding if you aren't going to make it yourself, is all that has to be bought...

The thought of using the rubber membrane is to stop the wicking of moisture up into the wood. Would it not be successful in doing so? I use 6mil EPDM to do the same thing in preventing moisture from entering the straw wall. I would assume it would work the same way here.


I think I already suggested it was not a good idea, and one that does rear up in the SB world that I feel is very unfortunate. Rubber is a condensing surface and should moisture get into a wall system for any reason this materials stops its egress immediately, and allows it to pool in the lower interstitial zone of walls...going undetected for years. I am very against "vapor barriers" in almost all their applications, and find that most often it is a "psychological element" of architecture and not one born out of "good practice" or historical evidence.

The next question typically is..."well, then what should be used..." In some cases perhaps nothing but the wood framing itself as I do not facilitate structural SB only infill systems, as the former are often fraught with issues (not always though.) If a stone foundation is employed then I would use gravel, packed clay, perhaps a lime layer, then more cob. I like cob mortar in SB...if SB is selected. I should also point out that SB by and large is not my preferred method of using straw at all. I like "clay slip straw" system way better for many reasons, yet SB is viable and a matter of choice or taste to a certain degree.

 
Kris Arbanas
Posts: 91
Location: PNW
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Jay C. White Cloud wrote:



Fair Oaks Pool Pavillion Project, Virginia. This shows the complete frame schematic with reinforced concrete with rebar and fiber cement that the county PE and ours agreed to. As a compromise, the posts sit on granite plinth stones with locking through bolts.



Hi Jay,
Could you please explain how the through bolt is locked into the beam? What is the best way to do this with a round post?

I'm assuming this is the finished product? http://static1.squarespace.com/static/53e8db2de4b02c4bc3af04fc/54d25d96e4b012e9db326091/54d25e34e4b02fc9b49eb035/1423072832954/Fair+oaks+Website-10.jpg
http://www.topnotchpostandbeam.com/fair-oaks-pavilion1/

I would like to use sonotubes for my pole barn and I am wondering if embedding smaller stone into the top layer of concrete would work well for blocking moisture collection and giving drainage. I know you would suggest other ways besides concrete but my limited time frame leaves me little choice at this point.
 
Jay C. White Cloud
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Hi Kris,

The "through bolt" into the post via a granite plinth was, at the last hour, thought not acceptable by local "authorities" of the "condo association." Funny how folks think concrete is stronger than stone...but it never has been. As for method of attachment into post, it passes into through an access hole drilled in the center of the post bottom up about 12", and then a locking washer, flat washer, and nut are secured to the through bolt via a small mortise cut in the side of the post that is later plugged.

Kris Arbanas wrote:I know you would suggest other ways besides concrete but my limited time frame leaves me little choice at this point.


Yes I would suggest a different way, first being opc is not as strong as stone and second the "limited time" issue. If...time is limited, adding several steps to a process like:

Properly mixing concrete...

Getting this into well centered forms...

That are properly laid out and ready...

Does not seem like anything that "saves time."

Anyone can choose whatever method they would like, but when I get a reference to "being stronger," or in your case..."saving time??"...I am not certain how adding steps to a process does this.

Like the Fair Oaks project, the concrete was actually anything but "time saving" and never will be a strong as stone posts alone. So if wedded to OPC tube footers, I would suggest just staying with that and charring and oil/waxing the area of the post bottom where it meets the concrete, and hoping for the best. Concrete will never outlast stone or traditional methods...it just isn't made of the same materials with the same viable service life spans.

If building a pole building, and no experience with stone footings and moving heavy stone, I would agree that concrete alone will be faster...though of much lesser quality in strength and durability, not addressing the other factors of opc materials.

Regards,

j
 
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