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Author Topic: Dry stone foundation for Timberframe greenhouse?  (Read 587 times)

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Offline Flekoun

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Dry stone foundation for Timberframe greenhouse?
« on: March 26, 2021, 05:32:03 PM »
Hi guys, I am building a timberframe greenhouse and now I am deciding on the type of foundation to use.
I am currently deciding between Rubble trench foundation and Dry stone foundation. I have few questions if anyone have any experience with this type of foundations I would be glad for any help.

1)Rubble trench foundation - I think I understand the principles. The trench need to be bellow frost zone. It is filled with gravel which serves as base of the foundation as well as drainage. Then there are stones put on top of the gravel and glued together with mortar. Ok. I like is as it sounds quite simple. However I am thinking about one modification and I am not sure if it wont make whole foundation unstable. The gravel type which is used to fill the trench is often used the rubble/crushed/sharp stones. However I have A LOT of pebble-like round small stones. I would love to use these insted of the sharp ones. I understand that they does not cling together like the sharp ones, but I think that if they will be in a trench, they have nowhere to move so I might possibly use them. What do you think.

2) Dry stone foundation. I love this type even more because it uses just stones smartly stacked on top of each other. I found a lot of references for Dry stone walls but not may for Dry stone foundations. The walls are build on the ground level, not under frost zone and allowed to move and heave when winter comes. Thats ok for walls but probably not for timber frame foundations? Do I need to dig a trench bellow a frost line and fill it with a stones and then build the wall on top of it? Or do I start building the wall "underground" and slowly build up until I am over the groun and burry the lower part of the wall under the ground? Anyone have any experience with this?

Please note the frost zone in my country is 1 meter deep.

Thanks for any advice!

Offline Don P

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #1 on: March 26, 2021, 07:09:43 PM »
The soil is usually not a rigid box, with the exception of the rock we just pounded into. When it is saturated my concern would be that your pebbles are going to push into the sides and your rubble trench may sink to varying degrees. Crushed rock isn't as prone to that.

The trench should be at least as wide as the gravel fill height. The rock should be 3/4"-.  Review R403.1(1&2) here;
2015 Virginia Residential Code - CHAPTER 4 (iccsafe.org)
The Superior Walls installation manual is a good read as well.

I'd begin your mortared walls a foot below grade to get into better trench sidewall strength, you'll probably be down into the firmer B soil horizon. Mortar is not glue, it has no tensile strength. It is a bedding material. Lay up just as you would if dry stacked, that is no outward slopes, the wall should be able to stand without mortar, then use mortar to help lock it into place. Dry stacked walls fail, that is what I'm working on now and have multiple times. Minimum thickness should be 16".
The future is a foreign country, they will do things differently there - Simon Winchester

Offline Flekoun

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #2 on: March 27, 2021, 02:29:17 AM »
Thanks for your advices! I agree with the pebbles pushing into the sides of thrench and thus squeezing unevenly. I probbaly have to let this idea go.
I have few clarifying questions. So if I am digging 1 meter deep trench filling it to 0.7 meter height with gravel then the width of trench should be 0.7 meters? It seems unnecessary wide trench to me.
If I understand correctly i should build the whole wall and after it is done I should “stuff” some mortar into the cavities? Or should I lay layers of mortar  gradualy as I am placing stones during the wall construction?
Thanks!

Offline Flekoun

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #3 on: March 27, 2021, 04:27:35 AM »
Also can you please check this guy. He is building beautiful timber-frame greenhouse but he is building the stone foundations directly on the ground without any trench? Am I missing something here or the guy is asking for a trouble during winter/floods?

Spring Fed Timber Framed Greenhouse Part 2 Stone Foundation - YouTube

Offline Don P

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #4 on: March 27, 2021, 08:29:20 AM »
That certainly looked like a recipe for disappointment but I didn't last long.
If you lay basically a double wall with the tops level or sloping inward, fill the center and place bond stones periodically that span the entire wall to tie it together is the easiest way. Coursed, 2 stones over 1, 1 stone over 2, thinner mortar joints, it is a bedding compound not a stone substitute. As the wall becomes thinner and taller it is more difficult to do that. More rock and thicker is actually easier and longer lasting in the long run. 

I have done a kind of hybrid concrete and stone wall where the backside is formed. Lay the stone face with mortar while bringing up the backside with pea gravel mix concrete to the form well consolidated to the rock and form.

For gravel footings take a look at this;
19 (superiorwalls.com)
The future is a foreign country, they will do things differently there - Simon Winchester

Offline Tom King

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #5 on: March 27, 2021, 09:32:44 AM »
We're getting ready to rebuild a 1798 dry stacked foundation because the whole thing had failed.  The intention is to make it look dry, but use mortar back in, so that you have to get down on all fours, and look in carefully to see it.

This is the only intact section left, because it was supported from inside the basement with an intersecting wall, and by a porch over the outside.

We've redone one chimney base, that was collapsing, and have another one to do.

These small, shim stones did not work for longevity.  I found out getting some heavy stones back in place in that chimney base, that any movement of the heavy stones above would just shred those small slivers.  That large stone is still in place because it had a Lot of nice, flat surface area, top, and bottom.




Offline Flekoun

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #6 on: March 27, 2021, 10:51:22 AM »
That certainly looked like a recipe for disappointment but I didn't last long.
I am not sure what are you referring to? My pebble idea?

Also what you are discribing is drystone wall or foundation? Or are they both the same? Because still not sure with the drystone approach if I have to go bellow the frostline or not. Thanks

Offline Flekoun

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #7 on: March 27, 2021, 10:53:09 AM »
We're getting ready to rebuild a 1798 dry stacked foundation because the whole thing had failed.  The intention is to make it look dry, but use mortar back in, so that you have to get down on all fours, and look in carefully to see it.

This is the only intact section left, because it was supported from inside the basement with an intersecting wall, and by a porch over the outside.

We've redone one chimney base, that was collapsing, and have another one to do.

These small, shim stones did not work for longevity.  I found out getting some heavy stones back in place in that chimney base, that any movement of the heavy stones above would just shred those small slivers.  That large stone is still in place because it had a Lot of nice, flat surface area, top, and bottom.


(Image hidden from quote, click to view.)

Is this drystone foundation just a stone wall of some height build on a ground or does it go deeper to the ground under the frost zone?

Offline Don P

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #8 on: March 27, 2021, 12:38:13 PM »
Quote
I am not sure what are you referring to? My pebble idea?
The video.

Go below frost line, do not use dry stacked stone under a permanent structure.
The future is a foreign country, they will do things differently there - Simon Winchester

Offline Tom King

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #9 on: March 27, 2021, 01:47:24 PM »
We're getting ready to rebuild a 1798 dry stacked foundation because the whole thing had failed.  The intention is to make it look dry, but use mortar back in, so that you have to get down on all fours, and look in carefully to see it.

This is the only intact section left, because it was supported from inside the basement with an intersecting wall, and by a porch over the outside.

We've redone one chimney base, that was collapsing, and have another one to do.

These small, shim stones did not work for longevity.  I found out getting some heavy stones back in place in that chimney base, that any movement of the heavy stones above would just shred those small slivers.  That large stone is still in place because it had a Lot of nice, flat surface area, top, and bottom.


(Image hidden from quote, click to view.)

Is this drystone foundation just a stone wall of some height build on a ground or does it go deeper to the ground under the frost zone?
This particular one got the triple whammy.  It was built right on top of the ground, then they dug the basement out some time later, and laid a single layer of bricks to hold the dirt back under the stone.  It didn't work.  Now there is a tumbled down pile of stones in the basement, and they kept stacking stones back to hold the house up.
Dry stonework needs to have a good footing, of some sort, under it, and every stone needs to be flat, top, and bottom with good surface area for weight bearing.

Offline Flekoun

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #10 on: March 27, 2021, 02:21:32 PM »
Ok, thanks guys. Thanks for your advices! So I will do the trench bellow frost line filled with gravel+stone and build mortared stone wall on top of it.
Just last question. Should I embed some steal rods into the wall itself, which will then be bolted to the timber sills and hold the structure in place? Or can I just lay the sills on top of the wall as they are without any fasteners? I guess the gravity and weight of the structure might be enough to not be afraid of any movement ?

Offline DonW

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #11 on: March 27, 2021, 05:45:07 PM »
I admire the old foundations, in concept and execution, for their simplicity and longevity. From what I've seen the structures built atop them were suited for what they were and their age seems to be a sufficient justification. Many of the newer approaches have more to do with the tendency of over engineering and risk of liability. Ok, the last is a reality which I can understand at the same time has nothing to do with the soundness of a building. A building that is that is calibrated to its appropriate foundation. 
Hjartum yxa, nothing less than breitbeil/bandhacke combo.

Offline Don P

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #12 on: March 27, 2021, 07:11:24 PM »
We'll have to agree to disagree Don. I've never worked on a building with a dry stacked foundation that was not in distress from the foundation. Very expensive and not my idea of fun. They kill a building long before its time. I can barely move right now and need to do repairs and pm on the bobcat tomorrow so we can hit it again next week. I'm getting too old for this... stuff  :D. A $20K siding job turned into a $200k job because the house was built on shifting stones. Floors are out of level about 5" and the damage transfers throughout the house. Like Tom's, someone dug a root cellar at some point that had one corner hanging by the siding and panelling. One house I worked on you could open the front door about 1/2 way and then the floor dropped away in 3 different directions. If the choice were mine I would have taken a picture and burned both of these even though they were only around a century old. I can think of four more right off the bat, same dry stacked scenario, the only reason they weren't torn down was misplaced sentiment. And no the damage didn't happen at a century, I was the third, and I hope final, repair on 3 of those, the rest showed signs of old long term settling and sagging. Do it once and do it right or it stands a good chance of biting you through the rest of time. Nope foundations are not fun or sexy, just put your head down, lean in and plow. We call it "getting out of the mud" and its a major day when we can work on a clean floor deck.

Flekoun, yes, if this is timberframe, embed steel to connect to the posts or sills. I'm "over engineering" on this job and hooking the sills to the foundation every 4', both sides of each corner and both sides of every sill splice. It's cheap insurance :).
The future is a foreign country, they will do things differently there - Simon Winchester

Offline DonW

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #13 on: March 27, 2021, 08:59:13 PM »
Fair enough, though I don't limit my foundations conception to this one form and also regard foundations in relation to the entire construction rather than only a staging for what comes atop them. Guess I should also include the nature of the earth where they sit. 
Hjartum yxa, nothing less than breitbeil/bandhacke combo.

Offline Flekoun

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #14 on: March 27, 2021, 09:25:28 PM »
Thanks! It makes me wonder how was this done in a past sice iron was very scarce or not available. How did they attachech the frame to the foundation? I guess they simply dont?
I am quite interested in doing things old ways but only to some degree where it does not compromise longetivity too much. Afterall I am doing a small greenhouse hobby project. Not a big house where I plan to live for generations :) so I can be more adventurous with experimentation and longetivity of few decades is good enough. 

Offline DonW

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #15 on: March 28, 2021, 12:13:06 PM »

Thanks! It makes me wonder how was this done in a past sice iron was very scarce or not available. How did they attachech the frame to the foundation? I guess they simply dont?
I am quite interested in doing things old ways but only to some degree where it does not compromise longetivity too much. Afterall I am doing a small greenhouse hobby project. Not a big house where I plan to live for generations :) so I can be more adventurous with experimentation and longetivity of few decades is good enough.


It seems like conditions that are suitable for dry stone. What's unknown is whether that method is used in your area and the nature of stone available there. For example, the stone in my area is volcanic and will not provide convenient stacking surfaces so I am hesitant to go that route. Remember such a foundation is also repairable in sections more readily than this monolithic construction. In my view of things reinforcement, poured concrete, embedded anchorage and so on and so on is really overkill in the situation as you describe. 
Hjartum yxa, nothing less than breitbeil/bandhacke combo.

Offline Don P

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Re: Dry stone foundation for Timberframe greenhouse?
« Reply #16 on: March 28, 2021, 03:30:49 PM »
Based on that I would consider post frame rather than sill on dubious wall. Treated posts (sleeved if organic) on frost depth spot footings, could be no more than a build up of 2x12x12" chunks alternating grain on a small pad of gravel each. Then the dry stacked wall sections, non load bearing, between posts. Build the wall low of the girts and a flexible membrane section or skirt board to allow the rock to heave or fall without affecting the woodwork.
The future is a foreign country, they will do things differently there - Simon Winchester


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