I'm thinking that this is my first post to the Timber Framing forum though I've been on the Forestry forum for a while. Starting to cut timbers for my proposed 18 x 16 "cabin". I'll be the first to admit I have little (read that as none) experience building. This will be my first timber frame project.
A nagging question is what to do foundation wise. My site is out in the woods, can get my tractor to it but not concrete truck. Also looking to do minimum site disturbance. There are a couple of trees which the cabin will be nestled between which I would like to preserve I figure that means not messing with their root system. The site is on a reasonable slope. Our frost line is 4-5 feet down.
Here is my current idea:
1. Place large stones on the downhill side of the site for "retaining wall".
2. Bring in crushed stone (front loader of tractor) and level the area uphill of the stones after placing some drain pipes Plan on having at least 6" of crushed stone at highest point of site. Compress stone as much as possible.
3. Place large flat stones on top of crushed stone to act to spread out weight of building.
4. build slip-form walls approx. 2 feet high on top of flat rocks to act as perimeter wall to set timberframe on using local stone and hand mixed concrete.
So how many things can you find wrong with those ideas ???. How would you do it?
Any suggestions appreciated.
Suggest checking with your building official. The UBC (uniform building code) requires foundations too be a minimum of 1'-0" below the surface and more is needed in freeze areas. Treated wood can be in contact with the ground but that is not recommended for a permanant structure. You may have more options than we do out west (unrienforced stone wall or footing).
The issue with the freezing of the ground is expansion. The degree of expansion is dependant on soil type, how much water is in the soil, how cold it gets and how long the cold lasts.
If soil with moisture is closer to the surface under one part of the structure than another you could get differential movemet ---- in other words one part of the structure gets heaved up more than another.
If there is a chance of a problem, suggest getting a local engineer or the building inspector to take a look at the site.
Here in NH I saw a guy lay down crushed stone as you suggest ,then used pressure treated timbers lap jointed together. He then built conventional stick built on top 16" on center with strapping and board and batts siding.(horse barn) I thought he was nuts, but he said as long as the water drained away it would work. It's been 6 or 7 years and the ridge is still straight and everything looks OK . I don't know how deep the stone is and he's not around to ask anymore.
not sure if this is ok for you since you have a slope but i went with the "pappy system" check out these threads.
Pappy's cabin (https://forestryforum.com/board/index.php?topic=7671.0)
My cabin (https://forestryforum.com/board/index.php?topic=22343.0)
I got the idea from Pappy. he used 24" dia, 4" thick cement blocks laid on the ground. Then I put pieces of treated telephone poles to my sills.
Got luck and keep us updated!
Sbishop
The old cabins around here used rock piers dug down to frost depth and stacked up to the sill. They often spat a rock and things settled, but mortar and good technique can improve upon that. Between these piers, later on as the family got time and money, they often built curtain walls of brick underpenning... pier and curtain wall. A pier under each post above, minimum.
I think you're retaining wall will prove too active for a solid foundation, I am working off a gravel footing now, they do work if done right but the gravel cannot move. We have about 3' of gravel in trenches 3' wide if I remember right.
I think what Tim is describing is what I know as a rubble trench foundation. It consists of digging a trench 16-20" wide down to just below the frost line. The bottom of the trench must be pitched with a 4" drain tile in it to remove water. The trench is then filled with crushed stone . A Mudsill system of 8x8 pressure treated timbers or otherwise rot resistant material should be used. In my area (which is similar to yours geographicly) I would plan on going 41/2 - 5 feet deep if possible with the stone. Another method would be to excavate the top organic soils and replace with a pad of well compacted gravel, lay down 18" round concrete pads level them and build of them.This method is requires some maintainence through the years and is similar to the old barns just built on rocks placed on the ground.
A thought from a place far away.
A dry stacked retaining wall tends to fall outwards, pushed one or two millimeters per year by frost. Sometimes they last well and sometimes not. Our frostline is 2 metres (6'4") and the hills are usually a mixture of silt and gravel and a lot of stones, dumped by the ice age.
I do not know the geology over there and is unable to give reliable advice in this case.
I am going to build a barn (30x50) and have thought about this myself. I think what Maineframer described is probably what was done .Forum members: I'm asking, do you all think this feasable in New England weather. It sure would help me to stay within the budget. I just don't want to be kicking myself later on.
My concept on this foundation was that I would treat it like they do the "floating" slabs around here. With them they level off an area and then put down a bunch of stone to make sure water doesn't accumulate under the slab. They then form up the slab and pour. They seem to work fine. From what I gather the fact that the gravel keeps water from accumulating, and freezing, under the slab keeps everything from heaving.
My thought was the lower retaining wall would hold the stone in place. I would lay perforated drain pipe on the ground and run the ends out through the retaining wall. I would then place gravel (cheaper) up to a certain point to level out the site behind the wall and then add the crushed stone. I figure with the underlying slope, drain pipe, and gravel, things should drain out pretty well.
I was thinking large flat stones for distributing the weight out over a larger area and then the stone wall on top to build on.
I should point out that there is no zoning in the town so no code which has to be met. Not an excuse for shoddy work but also don't have to meet set requirements.
As long as the retaining wall cannot move, its rocks need to be massive. I think you're talking about a lake of gravel dammed by the retaining wall. Pushing down on that lake is the weight of the building. If the gravel moves, so does the building. The rubble trench works, building gravel above grade seems risky to me. Thats where I'd start thinking of piers or a wall on the rubble trench.
I agree with Don P
Weight on the surface of ground immidiately behind a retaining wall adds greatly to the horizontal load on the retaining wall.
If the building is a cabin you do not need flat and level ground under the wooden floor. Concrete piers make sence to me. You can cast them one at a time. If the ground is clay or silt then piers are not so good.
I am no expert though.
The idea about the drainage pipes and having the water run off is great, until it's below freezing then this water will freeze and not run off.....
I appreciate the feedback. The comments all make sense. Again I'm trying to protect the roots of the trees which will be close to the cabin which makes me want to try to stay away from digging trenches for footings.
The comments would make me lean towards maybe putting the struction on posts to minimize the amount of root disturbance. I was hoping to use a stone foundation but not if I'm digging 5 foot deep trenches to make it work. Don't want the cabin frost heaving.
Catvet, Check out ------ technometalpost.com -------- a customer of mine has used these with success.
David,
Thanks for the link. Look interesting. Don't seem to have an installer in Vermont and I suspect I couldn't afford them for the project I'm doing.
(https://forestryforum.com/gallery/albums/userpics/10186/DSC02035f.JPG)
My office just sits on stones on the ground and we have not had the ground freeze more then a few inches deep in many many years. (Just got to love the South)
I would auger holes and pour in concrete for a bottom then sit post in on top with crushed stone or gravel around the post. It is a simple way to to do it. You can then align the post and saw them off level and lay down you sill plates on top and bolt down into them.
Arkensawyer,
I expect you are right that I will end up planting posts to support the structure. The feedback I'm getting both on the forum and in talking with people in the area is making me lean in that direction. I'm thinking of using Post Protectors (http://www.postprotector.com/index.html) to help preserve the posts longer and prevent uplift.
My next question is what to do as far as putting the cabin on top of the posts. My plans call for an 8 x 8 sill but probably the best I'll do with posts is 6 x 6.
Got any friends at the power co? :)
Hire out someone with a skidloader and 24" auger. You can special order at most lumber yards 24" forming tubes up to 8 foot in length. Rent a mixer and bag mix to fill the tubes, or use a front end loader to transport concrete from the truck to your site. If going with a slab, foam insulation around the perimeter can be used to negate frost penitration.
It is no problem to cast concrete pilings or pillars or whatever they are called. They will last much longer than wood. Wood below ground or directly on ground is only temporary.
Rent a concrete mixer, or buy a used one and bring there some aggregate and dry cement. You nail together some molds from ordinary sawn timber and put in some reinforcement bars and pour.
Pours up to 2 cubic metres are no problem if you get some friends to help.
TW how nice of you to assume I have friends ;).
Another type of below grade foundation system using wood is called the short pole system.
In this system only the part of the post below grade is pressure treated wood. Above grade you use regular wood and you sister a piece of pressure treated over the seam.
Like this:
(https://forestryforum.com/gallery/albums/userpics/10095/Short%20pole%20system%20drawing.JPG)
And if you get the pressure treated stuff that lasts 60 years you won't have to worry about it.
If it should rot out before then you just jack up or support the building and then remove and replace only the rotted lower section of the short pole system.....
Jim Rogers
Jim,
Interesting foundation system. Hadn't seen anything quite like that before, thanks.
I assume the sistering boards are on all four sides, not the two shown for illustrative purposes. I would also think you want to somehow seal the top of the connection (between non PT and sisters)
Jerry
Yes, well it depends on how your building will sit down over the short pole system...
Had a customer come in today that is building a pole barn way out in the country. He had bought some 1x8's and 2x4's a week or so ago. Seems he made open troughs that screwed together and had 2x4's around the middle and ends. He then cut re-bar to length and but his forms on a two axle trailer and went to the concrete yard and boutght 1 yard of concrete and had them mix and pour into his forms. Said that he moved over to the side in the shade after the pour and put in the re-bar and "J" bolts in the end where he drilled holes and took a nap. After the concrete sit up for a few hours he drove home with his piers. Said that he had to adjust the height by adding gravel to the bottom of the holes.
It's amazing the ingenuity that is out there. Not sure how I would get my forms filled with concrete out through the woods. Probably weigh more than my little tractor could lift.
I've been kinda debating how to tip up a concrete bent :D
Don, you just need a couple more guys thats all.
Did you say a "couple" more. :D :D :D How about 50 more? :o :o :o
Bruce
I'm finally getting geared up to build my little shed here for the farm, and I need to put it on some sort of foundation. The shed it is replacing was dropped on the ground almost 25 years ago, and is about to fall in on itself. The shed I'm building is going to be 8'6"x either 10' or 12'. The Sobon shed at Hancock is on a simple stone foundation that is simply sitting at ground level. Is there any reason not to copy this approach? Thanks.
Dave
Dave, in my opinion it will work just fine, do the maintenance, a yearly check and with a shim here and there. I have a number of small buildings here and they are doing well. I am also under the impression a 2" foam pad under a ground pad at ground level helps with frost heave. Tim
Dave,
A small shed can also be supported by thick wall 4" pvc pipe augured to below frost line and then filled with sand. Pretty cheap and easy and reasonable sure it will hold up to level and rot. There is a company that even makes caps to simplify the plastic to wood connection a bit if you like the pvc route. This has been done before.
I redneck like me might use some old 12" water tanks out back or telephone poles instead of PVC and save a trip to the home center.
I happen to have some telephone poles and a 3 pt auger so I would set them and then cut them level with a chain saw, but if you don't have poles, There was a thread on here recently were some one (logwalker?) was taking coper napthate and drilling angled holes in untreated wood after they were set below grade and topping the holes every few years with more napthate.
I find the pappy's system pretty interesting because it is simple but looks nice and professional... it got me thinking to a question no one ever managed to answer: when we speak of frost heave of soil, how much heave are we talking about? Is it a few inches, less or more? If it's a lot, it would seem that the window on a cabin that doesn't have foundation under the frost line would crack because of movement. If it's only a little, why are people building expensive foundation for cabin and garage when a simple yearly maintenance and shimming would be enough?
thanks
Alexis
Shimming when talking about a sawmill bed is different than shimming for a garage or cabin. But it would depend on how much of a nuisance shimming would amount to, and how often one would want to do it.
Frost heave depends on the soil (clay is bad) and the % moisture held in the soil. I'm on glacial till and get no frost heave, but 1/4 mile away they are on clay and get about 3-4" of heave.
Maybe that still isn't an answer .. ;D ;D
beenthere, that is a good answer, site dependent. Tim
That is the question isn't it?
How good to build it?
My father was a big fan of pole buildings made from saplings coated in tar and sided with rough cut lumber....I inherited the place and I think I MIGHT hit some rotted wood at ONE of the sites where he built them. I don't think they lasted 15 years.
AS I got a bit older I tended to sway to the IF YOUR GUNNA BUILD IT, OVERBUILD IT...WHEN IN DOUBT BUILD IT STOUT and 10 years ago I would have said give give the shed a full concrete basement...It will be your legacy.
But now I am becoming more like my father (GASP) ...well not that bad, but there is a happy medium between slap stick crappola that wont last the decade and stuff your great great grand kids will be using.
Now I sway to making things just good enough so that I wont have to deal with it again.
Here I'd go for the simplest dry laid stone foundation I could (ie: the big rocks under the posts approach).
That allows me to call it a temporary structure and "avoid any imperial entanglements".
For these small sheds (8'-6" x 10' or 12') my idea was to put it on skids so I could move it around. We have no frost heave so not a problem right?
Well, I ended up building a really nice shed that was 10' x 12' with a 10' wall height and a loft at the 7' height with sissor trusses to allow more room in the loft area.
I skided it into place on a nice flat area and put stacks stickered boards for drying in the loft then put fire wood in the bottom area.
As the rain hit and the gophers went to work the skids sank on one corner and the shed twisted which buckled a skylight I put in the side up by the eves.
The weight of the wood on the floor and loft was more than estimated. The soil bearing capacity was less than estimated.
This summer I ended up jacking the shed up and putting in concrete square footings to properly take the load. I am up to 12 - 94# bags of ready mix concrete and have probably 6 more to go.
Its a good idea to calculate your intended load and get enough bearing area to keep the soil bearing pressure below the allowable for your soil in a wet condition. :P :) :)
I have a 200 yr old TF barn sitting on a traditional loose field stone foundation. We jacked the barn up once in the last 50 years to "adjust some stones that have moved. See if you can find someone that still does this type of work.
I used to pour LOTS of grain bin foundations. The concrete was 6" thick in the center, and the outside 12" was 15" thick. We ran highway mesh through the entire floor with 3 bands of 1/2" rebar around the outside. Under this pad was at least 6" of fill gravel for drainage. This thickness sounds like overkill for your shed, but I have not seen any of the foundations move or severely crack- they do have the normal hairline cracks.
Charles
Quote from: Mad Professor on August 07, 2008, 07:32:45 PM
I have a 200 yr old TF barn sitting on a traditional loose field stone foundation. We jacked the barn up once in the last 50 years to "adjust some stones that have moved. See if you can find someone that still does this type of work.
I think it will probably be me that does the work. :D My boss is looking to get rid of 10,000 yards of marble quarry rubble across the street from me. I think I might know what I'm going to build the foundation out of. ;)
Dave
As to your comment re the tree roots being close...I'd think twice about leaving trees close to the building.
One of these nights, after all your hard work and expense is over, the wind is going to blow really hard. And every time it does so you are going to wonder if a tree will fall on the building.
I had this crazy idea for a foundation:
Why not use mafia blocks? these are the huge concrete block, usually 2X3X4. They are cheap and stackable. They could be laid directly on a gravel pad below frost line and you would get a full basement, even for a small shed or garage.
This must not work for some reason, because if it did, everybody would be using these!
Well, the first thing that comes to mind is that they are so large that they would be difficult to transport to the site and set in place.
Many years ago barns and houses used large granite blocks for foundations as it was readily available, then. You see these when you look at old house foundations. And there was a recent post about these large blocks in a thread on the guild site.
If you were to use them, one concern maybe, how would the connect to each other?
Would you lay them in some old fashion lime mortar?
Some people, like building inspectors, might be concerned that these blocks are not connected or fastened to each other as you would in a regular concrete block foundation. And if they aren't fastened to one another there is always a risk of the blocks shifting from outside ground pressure against the wall.
At guild conferences, during slide show presentations, we've see how old barns and other large structures have had their foundations (usually made of large blocks) shift over the years. And have to be completely rebuilt.
Without some type of rebar going from one block to another or some other method to fasten them to each other, I'd be concerned with using them......
But that's just me.....
Jim Rogers
I think the block could be drystacked, they are so heavy and they interlock so I don't think they could shift. I know that plow guy use them to build storage shed for salt.
If you do not trust that, you could use surface bonding cement as a mean to reinforce and to waterproof, you still would be way under the price of a typical foundation and I think it would be a lot sturdier with the 24" thick concrete!
Alexis
Do these blocks have keys or T & G to keep them aligned? Are they the one used by land scape companies to contain mulch and dirt? They don't sound cheep, what do they cost?
I am building a rubble trench foundation, loose boulders, smaller as I get to the top, pouring a concrete beam on top. Tim
Yes, they have some kind of groove and they lock....
they are 30$ canadian for a 2X3X4 block of solid concrete and yes it is exactly the type they use to contain mulch
If you have to get below the frost line? and want minimal disturbance.
I would use piers. A post hole digger on your tractor. Drill down to required depth insert Sona tubes then fill with concrete.
You can move concrete in a front end loader or rent one of those self powered wheelbarrows.
The soil type would determine if you could use sona tubes. With well drained soils and frost conditions you would be fine, but with loamy soils or clay the tubes will still heave and move all over the place. Tim
Anyone use the tapered plastic tubes? They come in a variety of heights. I've put them in for decks before. They have a fairy large foot print going up to about a 10" top. You set them and back fill them, and then mark them with a laser and cut them to height. Calculations are molded into the side for concrete volume. I wonder if the taper will prevent heaving? I've put them in some soggy clay type soil, and I haven't gotten any complaints. ::)
Dave
Dave, I haven't used them personally, but everything adds up, the tapered tube, the bulb base and frost will have a hard time grabbing hold. I don't see using a post hole digger though. I like the concept. Tim
Nope, not going to use a post hole digger for those. :) I generally put them so that there was 5' underground. They can be a pain to get them positioned and backfilled without moving them, but worth the effort.
Dave
Dave,
I used the plastic "bigfoot" forms on my barn and they work great. Mine used somotubes to extend above grade and that made it easy to mark and pour to a consistent height.
I only used these though because my 24x30 barn is 2+ stories and has the potential for alot of weight.
If I was buiding a small shed I would think they are over kill.
You could alway bury a rock onder your sonotube if you have a hoe. You will need to dig a hole for the "bigfoots"
With sona tubes I have heard it it best to keep the tops close to ground level. This is because they act as a cold sink and aid in the ground around them to freeze even more. The higher they stick up the more coldness they absorb. A foam pad around the tube just under the ground surface helps with frost penetration as well. Tim
moonhill
That sure makes a lot of sense.
Thanks for the post...as I'll keep that in mind for next time. :) :)
Shinnlinger, these werern't the real "Bigfoots", which are a base for a cardboard sonotube. I've used that style as well, but the sonotube has no taper. Have you seen the one piece style? They also work well.
I was on the phone with Jack Sobon a couple of weeks ago about a timber order, so I picked his brain about the foundation. He suggested a hand laid stone foundation. I have some marble quarry tailings on my place, and my boss owns the quarry which is a half mile up the road, so I will most likely be building a marble foundation for the shed. ;D
Dave
I like the sound of a marble foundation....especially at the price you are paying!
I stopped in at a friends place today for a five minute lesson in hand facing marble. It looks very straight forward, just a lot of DanG hard work. :D It only takes five tools. A 4 pound engineers hammer, a 5 pound splitting mash hammer, a 2" hand set, a 1" chisel, and a hand point. He wacked up a chunk of rubble into a nice building block in just a couple minutes. I'm sure there's a learning curve, but I should have the hang of it by the end of the shed foundation. 8)
Dave
and I bet you will be glad it it is only a shed after you point up the marble.
It sounds neat though. I almost bought a 2" roto drill to play with the hunks of rock I have around here.
I find Stone work very perspiring inspiring.