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grover
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# Posted: 15 Oct 2012 01:42pm
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Wife and I are in the process of buying almost 5 wooded acres to build a cabin. Very early in the process now but the plan we are looking at now is 598 sq ft (23 x 26) with 1 br on the main level plus a loft. The loft means we will probably need to go with a 12/12 pitch. I don't expect to be doing any building till at least next spring. Winter will consist of a lot of research and planning. We will do some sort of pier foundation and even that is still undecided.
A couple of questions about the foundation and floor platform...I have seen this done several ways. In all cases we will dig down past frost line and pour concrete footers. Here is where things can vary. Some do the sonotubes with rebar up to just above ground level and then anchor a 4x or 6x to that and attach their beams to the 4x or 6x. Some I have seen bring the tube up higher and anchor their beams directly to the concrete. Some set the posts directly into the ground with concrete then the beams. I even saw one built here locally with sections of telephone poles in the ground, I assume in concrete, and the beams on those. What are the advantages or disadvantages to each?
Also I see some put the beams all the way to the perimeter of the floor and some inset the beams in a foot or two. Why the difference with these methods?
I think with ours we will need a row or piers down the middle with a beam. A 23 ft span is a little too far for even a 2 x 12.
Right now I'm not even sure if we will be doing the framing ourselves. I think I'm skilled enough to do it myself but how long will it take with just me and my grown son helping vs hiring a framer and crew to get it in the dry quickly. Time and work vs cost is the issue.
Thanks
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grover
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# Posted: 15 Oct 2012 01:44pm
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Just thought of another way to do the foundation that I forgot to mention. Pour the footers up to around ground level and then lay a square of 4 concrete blocks filled with concrete and rebar. This would require each footer to be at or very near the correct level because the blocks are not easily trimmed to level.
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GomerPile
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# Posted: 15 Oct 2012 03:57pm
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Look into shallow frost protected slabs as a possible option.
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MtnDon
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# Posted: 15 Oct 2012 08:46pm - Edited by: MtnDon
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Quoting: grover Some do the sonotubes with rebar up to just above ground level and then anchor a 4x or 6x to that and attach their beams to the 4x or 6x.
Not a great plan. Too many connecting points. Think about 80 mph winds blowing against the side wall.
Quoting: grover I see some put the beams all the way to the perimeter of the floor and some inset the beams in a foot or two.
Works for a small building with no upper levels. Wider and taller buildings have too much weight to do a cantilever floor like that. 23 foot wide should have the foundation under the walls. Anything with an upstairs also should.
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grover
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# Posted: 16 Oct 2012 10:58pm
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MtnDon...I did plan on making the walls over the outside beams but I have seen the cantilever type and was just wondering why some do that. As far as too many connecting points I guess that is a concern so I will try to plan a full sonotube to beam foundation. I don't think that will be an issue because I don't have a lot of slope at the planned site. Might even put some anchor bolts in the sides of the concrete posts so I can have some cross-bracing.
What's your feeling on the concrete blocks dry stacked in a 4 block per layer pattern and filled with concrete and rebar?
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MtnDon
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# Posted: 18 Oct 2012 06:04pm
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Quoting: grover Might even put some anchor bolts in the sides of the concrete posts so I can have some cross-bracing.
If the piers extend any more than a foot above grade they NEED to be braced, IMO. Most piers, wood or concrete, are too small in diameter to offer enough surface area to the earth to prevent lateral movement. Many folks do not implement good bracing. There are ways and they involve more work ans materials than most DIY are willing, or think necessary, to do.
On the other hand four 8 x 16 x 8 concrete blocks per course present a large enough side surface area to be able to generate lateral resistance. If those were set on an 8 inch thick concrete footing with a footprint at least as large as the blocks (24 x 24) they would make a nice column. Rebar cast into the footing and bent upwards to fit into the core holes. Then extra rebar extending from footing to pier top. Fill with good concrete mix and agitate to eliminate voids. Cast brackets into the concrete to connect the beams. You may have to use some mortar between one or more courses to get the pier tops to be properly aligned and level.
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grover
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# Posted: 19 Oct 2012 05:35pm
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I have a friend who is a home builder so I will run this past him tonight over dinner. I didn't want to get him involved in the actual build mainly because the site is 1 1/2 hrs away. I know the soil is supposed to be pretty rocky there but I've not tried to do any digging yet.
I tried to do some soil data investigation at usda web site but it's pretty typical of government, pretty complicated.
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grover
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# Posted: 23 Oct 2012 10:55pm
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Mtn Don,
I have been reading your build thread. What did you do with or to your posts/piers to make them stable. I am seriously thinking about the bigfoot and sonotube method 6 to 8 ft apart and 3 rows.
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optimistic
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# Posted: 24 Oct 2012 12:03pm
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I looked into foundation methods myself before my current plan. I boiled it down to two options:
1. digging under frost, putting sunotubes down, add rebars, anchor in the wet cement those specialty steel braces for my beams (so the beams splices land on it and this steel holds it in place), then have a triple up 2x10 with bolts as beams. The joists the sit perpendicular on top of it.
2. Techno Metal post - these are helical steel piers that are driven into the ground, below frost of course, by a special machine (you need to hire the company)... It is very 'high techy' - the machine reads how much PSI is under it so you know exactly how much weight it can support. They provide you with an engineer signed paperwork. They will have a special steel brace, similar to the one you would have used for the application with cement I mentioned, that will fit your beam into. So with this plan you also have triple up beams but they rest on these steel posts rather than the cement.
Now, when I compared the price of both these options the cement option was a bit cheaper - you will be surprised how many bags of cement you need for those tubes - they have online calculators to show you exactly btw. So after calculating each thing I will need for my cement piers - including a rental auger which will make your life much easier, I decided that the steel post are a much better option.
It will be faster (one day they install all of them) - and digging so many holes in the forest is no fun... well, mixing 100 bags of cement is even worst which in my calculations is about how much I needed to do.... Also, it is stronger - you know exactly how much weight you can put on it. Lastly, it saves my health by not mixing and digging.
Besides, I am not sure where are you located but in my area of upstate NY there are a lot of rocks which people on these forum mentioned that are just a nightmare to encounter when you are digging for piers.
The steel tubes can actually adjust once they hit a rock..
I called the guy but I forgot the prices he gave me. I believe I wrote it on this forum and if not I have it in one of my many spreadsheets. Call them and ask how much it is or let me know and I will try to find my numbers.
This is the company I contacted:
http://www.technometalpostusa.com
Good luck!
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MtnDon
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# Posted: 28 Oct 2012 08:39pm - Edited by: MtnDon
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Quoting: grover Mtn Don, I have been reading your build thread. What did you do with or to your posts/piers to make them stable. I am seriously thinking about the bigfoot and sonotube method 6 to 8 ft apart and 3 rows.
I got lucky. I know more about piers now than I did when planning that cabin. I have since talked with two engineers and they tell me I was lucky. Lucky in that the soil is not really dirt; it is pumice from an old volcano that is extremely well compacted. I can dig a seven foot deep hole and the sides remain solid and even if left for a protracted period. It packs extremely well. The piers are about 42 to 46 inches average under ground and only 12 to 13 inches above grade. That makes a short lever arm. That said, neither engineer would sign off on it if there was a need to submit for a building permit. I have also since added a shear wall at each end between the end piers (across the ends) and from the end pier to the next on in down eachg long side. I have not yet added that to the topic documentation. I plan on doing that sometime.
(A shear wall is also called a braced wall; braced wall when built according to building code specs and a shear wall when designed by an engineer. Same thing different name.)
Basically a shear wall uses plywood to brace the wall against shear forces. (shear force is the force that tries to move the top of the wall down the length while the bottom stays put. This is what occurs when a pier is pushed laterally at one point such as a top or near top.) The plywood (3.4" PT in my case) is nailed to a framework just as in a regular stick built wall. Nailed every three inches they can absorb a lot of force.
If I was building again I would choose between a PWF or a concrete block continuous perimeter foundation, set below frost level, OR MAYBE Bigfoot System using 12 inch diameter sonotubes. (PWF = permanent wood foundation)
I was lucky. I know of others who have not been as lucky and have had piers shift, tilt and rotate. Before that cabin I always built on a on grade or raised concrete slab. I did not choose that for the cabin because of the volume of concrete. A transit mixer truck would have required a crawler tractor or 'dozer to drag the mixer up the final hill.
8 foot spacing can work if the beams are robust enough. 6 foot makes that easier and 7 foot would be a compromise.
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