Need info on post foundations in the rocks/mountains.

[jrkimroxie]

Just finished milling my 6"x 12" SYP logs for our 32'x32', 1.5 story log home. The home will be near Hot Springs AR. in the hills/mtns, and the only "LeVeL" spot is on a 1/2 acre rock. My plans are to build on conventional foundation using treated 6"x6" post on 4' centers on all 4 outside walls, sank 3' into the rock using drilled holes. House would be 1' off rock on low corner, and 4'-5' off rock at high corner. My primary concern is if this post and spacing configuration is sufficient for the exterior weight bearing walls, since the top floor will be built from free-span trusses and all house weight will be basically distributed to the outside walls and foundation post. A excavation company with a D6 dozer and a ripper could do nothing with this rock, and after 4hrs and suggested drilling into the rock & using post foundation.

[Stephen1]

I'm sticking my nose in here, hoping for some pics and to learn something.
What kind of rock?
Why do you need to go 3' into the rock, seems all full deep if u are on rock.
Are the 6x6 going in the rock or will it be on pipe with brackets or saddles to hold the 6x6.
What kind of rock?
My cabin is on an ICF foundation but then we have a winter here and a need to keep the basement warm.

[Jay C. White Cloud]

Good Day jrkimroxie,

I'll add my "two cents," hope it helps or gives you some ideas.  I build timber frames and use traditional methods almost exclusively.  That includes natural stone foundations.  I have posted these pictures on other threads, so sorry about the repeated posting, but they really are the best examples to show you and give you an idea of what you can achieve.

This is what you can achieve too, (with a little guidance,)!!! ;)


four story house sits on this


diagram of one method of attaching.


This was one of my student's projects.


Stone has been and is still is a perfect foundation method and what you describe sounds viable.  I would like to know more and see pics of the building site.  That would really help.  I think there are some elements to tweak that could save you time and some money.  My house is built on Vermont ledge and packed gravel.  If I had used a conventional foundation with 200 mm (8") concrete wall it would have cost over $65,000.00 including the blasting they wanted to do. They wanted to blow my beautiful rock, that has a psi greater than  4500 kilo (10,000 lb) and replace it with concrete, that at it's best might achieve 2000 kilo (4500 lb.) "Silly rabbits," what are they thinking?

Post pics, and let us know how things go?

Regards,

Jay

[Ironwood]

Nice, and the "silly rabbits" is great. Just cause the book says "_______________" you should do it our way instead of the BEST way. Good for you.


Ironwood

[Jay C. White Cloud]

Thanks Ironwood,

You might like this little story, it ties into what folks all over are trying to do and the "blockader" others seem to always be throwing up against them:

Going back almost ten years, I was called in to consult on a project involving a horse barn.  The client knew, besides being a timber wright, I also had been a zoo keeper.  (I had at one time aspired to get a PhD. in Animal Husbandry and Ethology.)  She had been getting advice from her G.C., Architect and P.E. that didn't "sit well," with her. 

There was a beautiful late seventeenth century barn on the property that she wanted to add an equestrian center to.  The barn had been kept in immaculate condition and needed little in the way of restoration.  I was to help facilitate the addition of another timber frame onto this existing historic structure, to function as stables and arena.  She wanted it to comply with current standards for equestrian husbandry but also follow the theme of the existing architecture the barn offered.

She had been told that it would be difficult, to impossible to accommodate her request.  The original barn, of course, sat on a "dry laid," stone foundation and would not be adequate for the new addition, (according to her "experts.")  When she pressed for an explanation, they stated, that "you just can't build that way anymore."  Wanting a better explanation, she asked for a meeting with me present. 

To say there was "tension in the air" would be an understatement.  From the beginning, the conversation was adversarial and accusatory.  There was no exchange of ideas or questions on their part.  They immediately, but more bluntly, stated what they had told the client, but this time aimed it in my direction.  There was an exchange of; "you can't build that way, it is too unstable and will "frost heave," undermining the building the first winter."  I stated that, I do indeed build this way, as did the original "barn wrights." That structure hasn't "heaved," in over 150 years of service and neither will the new one.  "Concrete is stronger and more stable," was the retort.  I simple said, stone on average has three times the psi of concrete and stability is a relative description.  I went on to explain that; should there be any kind of severe climatic or seismic event, concrete would endure no better than stone, the difference being, with stone, we could very easily re-service the building.  With concrete the structure would have to undergo expensive restoration and the concrete removed, for it would be unserviceable after such an event.  Concrete holds, till it doesn't, then it fails catastrophically, dry laid stone does not.  This banter went "to and fro," for sometime.  Needles to say, a new P.E. was found, the G.C. refused to comply and left, and the architect rapidly change his tune, (or his wife changed it for him, she was the client! ;))

Jay

[jdtuttle]

Simpson strong ties have several products that would work. What I like about these connectors is there is no stone to wood contact which will help resist rot.
http://www.strongtie.com/products/connectors/cps-pbv_apg.asp
jim

[Jay C. White Cloud]

Simpson strong ties have several products that would work. What I like about these connectors is there is no stone to wood contact which will help resist rot.
http://www.strongtie.com/products/connectors/cps-pbv_apg.asp
jim

Hi Jim,

Please don't take this in the wrong light, but when I hear someone make reference to "Simpson" products in this fashion, I must make note of it.  I like "Simpson" products and we often apply them to address additional safety backups to frames that are built in seismically active location.

However, if done correctly there is absolutely no concern with placing wood support members directly on stone plinths.  It has been done for thousands of years and the oldest structures in the world, (2000 plus years old ) sit on stone plinth foundations.  They have weathered, wars, atomic blasts, tsunami, earthquake; and are still going strong!

I don't counter your advice, in some application the "post extensions" that "Simpson" make are the item to use, but not always.  When I see them "spec'd" by an architect/designer I often can facilitate a more aesthetically pleasing option.

Regards,

Jay

[Ironwood]

Great story, thanks.

Ironwood

[Rooster]

To help answer the question about post spacing, what type of frame system will the floor be supported by?  Will the floor be independant of the log house, where as the log house will be built on top of a house deck?...or will the lower coarses of logs be part of that system?

As to the connection to the rock face, I have used Timberlinx http://timberlinx.com/index.html  with their very stout 8 x 7/8 in. expansion anchors to secure posts to the top of columns.  If you can drill a 7/8 in. hole into the rock, then the anchors will work.

This is a connector unit AB675... which threads onto the end of the 7/8 in. anchor bolt CA08.

  

 

[Jay C. White Cloud]

Hi jrkimroxie,

"Roosters," post is spot on.  The two photos he has presented work in concert with each other and we have applied them on several occasions.  You can also use his second photo as a stand alone anchoring method, with the caveat that you must match it to the potential load deflection criteria.  If you aren't up to that task, seek advice from a P.E. or the manufacturer of the attaching apparatus.  Good luck and keep us up to date on what you discover.

Regards,

Jay

[jrkimroxie]

 My plan is to drill holes into the rock, set 6x6 treated poles, and use 2x12s for floor joist. Planning to use a supported joist in the center of floor frame, so the 2 x 12 floor joist will only be 16 foot span on 2' centers. Then lay a plywood subfloor, and stack the logs on top of that for the exterior walls. My question is using the 6x6 post and 2x12 floor framing, will the post need to be on 4 or 8 foot centers and how deep to drill into the rock? I have some pictures of the rock hill on my phone that I must figure out how to post to the forum.

[SPIKER]

j Roxi:

from above posts you don't have to DRILL any big holes deep into the rock at all. 

The 6x6 Treated Posts can be set onto small anchor pins that are epoxied into the rock.   The HOLEs are smaller and are filled so no moisture can get into them to cause longer term rot/decay or worse water freezing & cracking out the rock.

OR the 6x6's can be attached with 4x4 angle iron (box frame) that is anchored to the rock and then posts are dropped into the angle box frame.   you can first pour in some epoxy to level and add the posts into curing epoxy or let the epoxy cure at a LEVEL and the posts sets dry on top in the angle box frame.   If you WANTED you could even cut/drill/stack rock around the post base to HIDE the angle box frames.

Bare in mind that some code enforcement areas may require structural stamping on plans or engineer approvals regardless of the method of attaching.

Mark

[Jay C. White Cloud]

Hey jrkimroxie,

I would go with 1200 meter (4') centers, but must concur with SPIKER, that you may be wise to seek advice from a P.E. for stamping approval.  I also must deffer to others on the forum, because you are mixing methodologies from what I can glean from your description.  I only use heavy timber construction methods and you seem to be building a "stick frame" foundation that you intend on "capping" with a log structure.  I have not seen these ever fare very well but, that is my bias, and "I own it."  You could be fine doing it.

Whether this is going to be a traditional log, (or hybrid,) structure, I must ask why you would not use a more traditional foundation, as normally found under them?  SYP would be fine for post, (there are treatment methods if you are concerned about decay,) and then you could build a log and timber foundation frame to support the log structure above.  This would achieve better architectural equilibrium.  There really isn't any need for 2x stock and PT.  What do you think? ???

Regards,

Jay

[frwinks]

How much of the boulder gets buried in the ground?  Is is just placed on undisturbed soil?
I have 12-14 porch posts to set and would love to use granite boulders from our property as "footings".  Love the look, the concept, the whole works.
Jay C, you wouldn't happen to know a PEng in Ontario brave enough to sign off on this, would ya ??? :D  Mine has been great on a lot of wild things, but this might just be pushing my luck with him :D
   

[Jay C. White Cloud]

Hi frwinks,

It is funny you would mention recommending a P.E. in Ontario.  ??? I was just on the phone yesterday talking with Ed Levine about issues with P.E. involvement over the past couple years, and the increase with their population at the TFG and in our timber framing field in general.

I, (as Ed also observed,) have had some real "run ins," on the subject of "deflection criteria" over post to plinth attachments.  Many P.E. have come to timber framing and only have a P.E. background and try real hard to "push," their belief systems, (and math,) onto a field that has been around for thousands of years.  Ed is a generally sweet guy, that when pushed into a corner, will point out that "bumbled bees can't fly, according to engineers," but somebody forgot to tell them.  The gist of his jest is whether you are an architect, p.e. or related, you should really cut a few frames, and look at some really old ones, before you tell someone that what they are about to do, "won't work," since quite often not only does it work, it has for a very long time.

Ed was just giving one of the young fellows in our co-operative timber framing group some assistance with a project down in the Virginia/D.C. area.  We called Ed, because a TFG recommended P.E. stated that the frame, 4.8 m x 7.5 m (approx. 16' x 24'), could not be made of White Pine-it must be "pressure treated lumber", the post must be a minimum of 200 mm x 200 mm (8"x 8") preferably larger, and their was not adequate bracing.  This was just the start of his issues with the frame.  Needless to say, he is not going to be used, now or in the future. Ed thinks I should publish an articular, (or minimum a letter,) in one of next years TFG publications addressing the issue of P.E. with no timber framing background giving advice on timber frames.

If you really need a recommendation, I could look into it for you?  I'm sure Ed will have/does know someone.

I'm going to try and post some more pictures of exactly what you just described you want to do for your porch real soon, just hold on.

Regards,

Jay

[frwinks]

Thanks for that story, I'm sure a lot of us can relate...  We (PEng and I) have a give-take relationship ;D  I give him 12x12 ridge beams where they're not needed, I get a modified enclosure/insulation method  ;D  etc...
Looking forward to your input and if it's not too much trouble, the contact info of the PEng.  I don't want to end up with 4'x4' 18" deep footings holding up the granite boulders :D
Cheers,
Raff

[Jim_Rogers]

If you go to the timber frame guild engineering council website there is an option there to "find an engineer".

You will be taken to a page that shows a map of north America. Click on the state or province you want to find a timber framing engineer in and you'll get a list of all the engineers registered with the council.

You can visit their websites or call them to get more information about their services.

Good luck with your search.

Jim Rogers
Member of the Timber Framing Engineering Council (as well)

[Jay C. White Cloud]

Hello Jim,

This is where the young man I referenced above got the P.E. name from, and why, I think both Ed and I are concerned.  We have way too many folks; "jumping into the timber framing, kitchen with recipes they say are great but, they don't cook and have never really tasted the meal."  What do you think?  ???

Regards,

Jay

[Stephen1]

How much of the boulder gets buried in the ground?  Is is just placed on undisturbed soil?
I have 12-14 porch posts to set and would love to use granite boulders from our property as "footings".  Love the look, the concept, the whole works.
Jay C, you wouldn't happen to know a PEng in Ontario brave enough to sign off on this, would ya ??? :D  Mine has been great on a lot of wild things, but this might just be pushing my luck with him :D

I see you are in my neighborhood, or a least my province. The "Hills" could be anywhere, but only few with granite.
Try Steenoff Building services in Orrillia. He was willing and able to take on my project partway thru. I also have been talking to him about about my next project. I do believe it will take you a bit to find someone to agree with what you want to do, especially in Ontario with the new building codes put forth this year.

[Jim_Rogers]

Hello Jim,

This is where the young man I referenced above got the P.E. name from, and why, I think both Ed and I are concerned.  We have way too many folks; "jumping into the timber framing, kitchen with recipes they say are great but, they don't cook and have never really tasted the meal."  What do you think?  ???

Regards,

Jay

Well, of course you have to do some checking out of the engineer and ask for references or experiences from them. Just like you'd hire just about anyone. If they are put off by that then you have just found a clue that they maybe hard to work with.

Everyone has to start someplace and you shouldn't automatically dismiss a beginner, we were all "beginners" at one time.

If his suggestions are un-reasonable, then I would say question him. And of course you can always get a second option.

Jim Rogers

PS. I have heard of timber frame designers who have never cut a frame before. And I suppose that there are timber frame engineers who haven't either. Hands on experiences can be the best teacher. Maybe a simple question like: "have you ever cut a timber frame joint?" would be in order.

[beenthere]

Jim
You mean like a writer who has never written a book before?
As you say, we all have to start somewhere and finding out one doesn't know it all in the beginning is the school of "hard knocks". The young PE will find out the same thing, and soon learn that what he/she assumed from the book learning and the multitude of National Design Standards, there is more to it in a real application.

[Stephen1]

everyone has to start somewhere, but it is really nice if you can find the experienced person in what you are trying to do. Better than reinventing the wheel

[Jay C. White Cloud]

Thank's Jim,

That makes me feel better about some of the "off-line," conversations that I have been having about this subject.  Ed and I came to some of the same conclusions you just shared and in one way or another, what you suggested has been and/or are being done.  Jeff has only been timber framing for a short time and is still a little "green," so his "vetting" skill are just developing.

Thanks for engaging in such an elementary question as I presented to you, (part of me was reluctant to ask it,) but I knew that there are a number of folks, of varying skill sets that would benefit from this short exchange about P.E. vetting and engagement, including myself.  I find it a good idea to always get a second, (third or forth,) opinion when you are not sure if you are on the right track.  Thank' again.

Regards,

Jay

[frwinks]

I see you are in my neighborhood, or a least my province. The "Hills" could be anywhere, but only few with granite.
Try Steenoff Building services in Orrillia. He was willing and able to take on my project partway thru. I also have been talking to him about about my next project. I do believe it will take you a bit to find someone to agree with what you want to do, especially in Ontario with the new building codes put forth this year.

Thanks for the lead Stephen, they're north east of us actually, we're just south of Creemore.  The granite boulders I pulled out while excavating our basement.  A real PITA when you're not expecting them and are working with undersized equipment, but hopefully I can put them to good use now.
A nice thing about building with unconventional materials/methods is that, once stamped by PEng, all the building inspector has to do is admire the work and learn a thing or two.  Makes for happy inspectors ;D

[Stephen1]

A nice thing about building with unconventional materials/methods is that, once stamped by PEng, all the building inspector has to do is admire the work and learn a thing or two.  Makes for happy inspectors ;D

For me the building inspectors turned down my log cabin at first, and got quite rude and insulting. The town then got rid of that inspector as I was not the only unhappy builder in the township. The new building inspector showed up as you said, with a smile, commenting on how nice and qauint my cabin was, and wanted to know what all the fuss had been about, after my plans were stamped by 3 different PEng
steenoff used to have my cabin on his computer as his screensaver after he passed my work. 8)