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Author Topic: Question re pier and beam for timber frames  (Read 687 times)

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Offline rcsmith2

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Question re pier and beam for timber frames
« on: August 12, 2022, 08:44:46 PM »
Hi everyone, Iím just beginning to think through a build of a small timber frame (18í x 27í ish) cabin.  Iíve seen a lot of different foundations, but I was wondering why pier and beam foundations are mostly absent.  

Letís say you laid beams across piers running the length of your building, and then used mortise and tenon joinery to erect the bent directly on the beams (i.e., a tenon from the bentís posts going into a mortise on your foundation beam).  Assuming you spaced the beams closely enough that you didnít have a problem with the joist span between them, and that your building wasnít going to topple/blow over, is there some other reason this type of foundation doesnít appear more often? Is it just a preference for having the posts tied directly to a pier? Iím sorry that Iím not yet more familiar with drafting programs or Iíd try to give a picture. Iíd be interested to hear thought and whether anyoneís seen/done this.

Online Don P

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Re: Question re pier and beam for timber frames
« Reply #1 on: August 12, 2022, 09:12:18 PM »
Let's look at what the building code says.

R403.1 General
Quote
All exterior walls shall be supported on continuous solid or fully grouted masonry or concrete footings, crushed stone footings, wood foundations, or other approved structural systems that shall be of sufficient design to accommodate all loads according to Section R301 and to transmit the resulting loads to the soil within the limitations as determined from the character of the soil. Footings shall be supported on undisturbed natural soils or engineered fill. Concrete footing shall be designed and constructed in accordance with the provisions of or in accordance with ACI 332.

R404.1.9.3 Masonry piers supporting braced wall panels.
Quote
Masonry piers supporting braced wall panels shall be designed in accordance with accepted engineering practice.

To carry the lateral loads of the house safely to ground the easiest way is to continue to transmit those forces along walls just as above. If you choose to collect those forces and transmit them through piers an engineer's stamp is required. Post frame construction, engineered "pole barns", typcally runs the posts unbroken from footing to roof plane. This is the simplest way to avoid hinges in the lateral load path. What you are proposing is sometimes referred to as a "soft story". In high wind or seismic the foundation posts or piers overturn where foundation walls of some sort are braced against this. The lightest masonry configuration of this is called pier and curtain wall. Individual 8" piers are spaced around the perimeter and 4" thick brick curtain walls are built around and tied to them. The thinner 4" wall is load bearing but primarily braces against lateral loads. This is good up to 4' tall and with no backfill around it, so we see it mostly in the south. Then the foundation walls typically become 8" masonry.
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Offline Chilterns

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Re: Question re pier and beam for timber frames
« Reply #2 on: August 13, 2022, 03:22:36 AM »
The practice of standing timber-framed buildings on top of short pillar type foundations is not new. In England this was common practice for granary buildings that were stood on top of staddle stones.



The mushroom tops of the staddle stones were thought to help prevent vermin (rats & mice) from gaining entry into the granary. The staddle stones stood on top of brick piers buried below ground level.




There was a second but less well known reason for adopting this practice and that was if the building was anchored or secured to the ground then it would have been deemed to belong to the landlord and thus tenant farmers would simply set their chattel buildings free standing on top of short pyramidal stone type pillar foundations. The passage of centuries has demonstrated that this building practice is perfectly satisfactory but probably not to be recommended in earthquake zones.

Offline Ianab

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Re: Question re pier and beam for timber frames
« Reply #3 on: August 13, 2022, 03:51:18 AM »
That's a valid idea. Keeping wood out of ground contact means it's going to last maybe 10X longer.  The piers / piles can actually be replaced if needed, without compromising the rest of the structure. More modern methods might use a plastic or tar barrier layer, but same idea.  

It's common here in NZ, but like the UK we don't get the really harsh Winters with solid freezing. If you have frost heave. then building foundations need to be different. But in a wet temperate climate, keeping wood off the ground is more important. 
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Offline Chilterns

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Re: Question re pier and beam for timber frames
« Reply #4 on: August 13, 2022, 04:05:23 AM »
I just received this pic from Andrew Heald featuring the use of recycled American shell cases that have been used to support timber building in Laos.



I wonder if this practice features in the building codes ?


Offline Ianab

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Re: Question re pier and beam for timber frames
« Reply #5 on: August 13, 2022, 05:26:33 AM »
Probably meets the code for termite resistance?  :D
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

Online Don P

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Re: Question re pier and beam for timber frames
« Reply #6 on: August 13, 2022, 06:17:33 AM »
Easily solved. Compare the near house on shell casings that are overturning with the one directly behind it with unbroken posts from footing to top plate. That unbraced hinge between pier and floor beam is not a good thing.

Scandinavian's developed that granary style, I suspect what you are seeing is what it later devolved to locally in the millennium after William the Conqueror. In Viking style those pier posts are braced quite well. Each builder is an individual, this one was good!


 

Notice in both cases that the original braced foundation elements were later sorta copied but without the bracing elements. Whether out of immediate need or ignorance it is impossible to say. Then time goes on and people start saying that this is a good and proper way to build. The next natural disaster happens, people blame their maker, put their thinking caps on and improve, for awhile and then we repeat.

Now, Gentlemen, you are desiring to have this person build something that you know is potentially going to land him in hot water with the authorities. This is not the first time I've watched this happen. A decade or so ago there was a young family on a cabin building forum posting pictures of their DIY pier and beam cabin going up. I recognized the location, right down the road. I warned them twice online but was pretty much shut down by smarter folks that were telling these people what they wanted to hear. As I would pass by I noticed the progress and when it got up to the second floor walls, I guess the inspector noticed it and shut the project down. It lingered in various stages of gray through that summer and then was removed. I drive by that overgrown site daily now. I've never seen them again and I've never seen a for sale sign. Looks to me like a dream crushed, or delayed till after the kids are grown, they will never get to enjoy a youth spent on the river. Please understand the consequences of your words.
The future is a foreign country, they will do things differently there - Simon Winchester

Offline kantuckid

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Re: Question re pier and beam for timber frames
« Reply #7 on: August 13, 2022, 08:49:48 AM »
My current off-grid, 16 x 20 log cabin project is sitting on concrete piers with hot-dipped galvanized J-bolts in the tops securing the 6x10 oak beams. One of our sons is a licensed civil engineer and does this stuff daily on a much larger scale than his Dads hobby build. He calculated the wall loads and pier base dimensions for me. I used 24" sq plastic form bases with paper tube forms. I have alu termite shields on my pier tops and a sill seal layer to isolate the wood beams from the concrete. 
My pier bases were placed below freeze line in three trenches to locate 9 piers, one is centered and has beams connected to all side beams in four directions. I chose to use 24" as my minimum splash zone distance above grade on a slightly sloped site. My larger issue is the tight build site thus that my tractor can only reach three sides, so I bought a Super Genie to raise backside logs which is unused so far.
Currently I'm finishing my 2nd log run by myself while my so-called helper plays somewhere. Logs are 6" thick D-logs and a new type of build for me what with flat inside wall surfaces.
Locally we have zero building codes that apply to me nor any zoning requirements, so what applies is good building practices. 
The plastic form bases are sold in several brands, round and square and utilize stepped sizes of tube forms which do come in a lightweight paper and a heavier version which I used. Given my forms were poured back in the woods, foundation issues were no ready mix, thus what carries the load with minimal bags of mix to tote. My main expenses were for a backhoe to dig three trenches and a helper to mix and pour the forms. 
My foundation would easily carry either a timber frame or the logs I'm using. 
The foundation is as simple as is possible but far more substantial than lots of old barns I drive by sitting on rock piles for the past 75-100 years. :D
 FWIW, it sat for 2 years (backfilled and plastic sheet covered with crushed rocks and beams fixed in place) while I searched for an EWP logs source. last year I painted it with a solid stain while it sat in the weather exposed. 
 Once I finally found the logs, I built the floor system inside the beams and covered it with a 4/4 subfloor.  I flashed the entire perimeter from the subfloor before I placed any logs.
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Offline Tom King

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Re: Question re pier and beam for timber frames
« Reply #8 on: August 13, 2022, 12:26:07 PM »
The first 200 year old house I worked on was a 1777 house that we redid in 1977.  It was a Low Country farmhouse down near Wilmington, NC.  It was sitting on 3' cubes of Heart Cypress, right on top of the sandy ground.

The 3' cubes of Cypress were completely fine except for some erosion under the bottoms, but they still measured 3' square on all sides.  The owners wanted those pulled out, and a masonry foundation built.

There was no sign of termites in those blocks, or any part of the house sitting on them, but someone had put a set of Yellow Pine steps on the rear of the house.  Termites followed those steps up, and consumed one of the corners of the house.

Being where it is, it was lucky that no hurricane had ever hit it, because there was nothing tying the house down to those blocks of wood.  We jacked up the house, and rolled them right out from under it.

There are still old houses "Down East" in North Carolina sitting on those old blocks of Cypress.

Offline Chilterns

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Re: Question re pier and beam for timber frames
« Reply #9 on: August 13, 2022, 12:42:20 PM »
The original enquirer stated :-

"I'd be interested to hear thoughts and whether anyone's seen / done this".-

I replied to that request i.e. re "seen".

Don P stated :-

"Now, Gentlemen, you are desiring to have this person build something that you know is potentially going to land him in hot water with the authorities."

That is not and never would be my intention and hence you should withdraw that remark which is completely out of order.


Offline Chilterns

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Re: Question re pier and beam for timber frames
« Reply #10 on: August 13, 2022, 02:52:08 PM »
Following Mr King's valuable input I was reminded by Dr. Chris How of early Australian building practice where timber-framed buildings were perched on top of "stumps.




This approach is a hybrid between Olde English practice and North American pole barn practice where either tree stumps or lengths of log were up ended and buried in the ground usually using durable Eucalyptus or Messmate timber.



These stumps have survived now for some 150 years and reflect a true approach to vernacular building i.e. building using available local materials (cement / lime mortar was unlikely to be available at the original time of construction).

I have come across another picture of a staddle stone granary foundation taken whilst under construction in April 2021 that shows more clearly the interface between the staddle stones and supporting brick piers.






Online Don P

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Re: Question re pier and beam for timber frames
« Reply #11 on: August 13, 2022, 03:15:51 PM »
He is obviously seeking construction advice.  I'm not going to parse the definition of seen. I quoted the law, you seem intent on showing pictures of non compliant work and representing it as perfectly satisfactory. 

Pier and beam is not prohibited, it requires engineering. That has not always been the case, it earned that status after a rich history of failure. The reason the house I saw was removed I suspect is because the builder could not find an engineer to sign off on that substandard foundation.

Our controlling lateral force is not seismic, it is wind. For me, take the height of the ridge x the length of the wall. Multiply that area x 20 lbs per square foot of wind force and there is the design lateral force. Bracing elements and anchors need to be shown capable of safely delivering that force to ground. As can be imagined, these historic foundations will not pass that bar.



The future is a foreign country, they will do things differently there - Simon Winchester

Offline rcsmith2

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Re: Question re pier and beam for timber frames
« Reply #12 on: August 13, 2022, 07:46:44 PM »
Thanks everyone for your answers and insights.  I shouldíve mentioned that Iím not remotely worried about strict code compliance (Iím over a mile in any direction, in forest, from a road and own everything in between), but itís nonetheless very informative to read the code and use it as a guideline.  The pier and curtain idea is intriguing.  I also shouldíve been clearer that I wasnít talking about wooden piers between the footings and beam - I agree that just looks like a disaster waiting to happen.

The straddle stone granaries were kind of exactly what I was picturing! Itís interesting to see it, and Iíd never heard/read the word ďstraddleĒ in that context before! Iím amazed by the knowledge of techniques and history here, thank you all so much for lending me some of it.


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