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

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.

First, will this project be subject to a building code? Pier foundations may not be approved by most codes, but then there are places that do not have or do not enforce construction codes.

QuoteSome 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 - 90 mph winds blowing against the side wall. Pier foundations are often inadequately braced as it is. High winds are not all that uncommon. By the time adequate bracing is done on something the size of this, the cost goes up and you are still likely guessing at the foundation.

One of the better pier foundations are based on the Bigfoot Footing System. Google that. Even those will not be approved under most codes.

QuoteI 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, IMO. Anything with an upstairs also should.



20 feet width is the limit for 2x12's and at that the 2x12's should be "select structural" grade, not the usual #2 you find. An alternative to using a center beam would be floor trusses or manufactured floor joists.





Other types of foundations such as concrete slabs work well in some climates. Shallow frost protected foundations are a good alternative too, but if the building is not heated full time through the winter there are extra considerations that must be addressed. Full perimeter footings with a block or concrete wall (making a crawl space) offer a very stable foundation almost anywhere...

Ok, so no 4x's or 6x's anchored to the concrete although I see that a lot on here (with cross bracing of course). 

In a 23 or 24 x 28 cabin with a loft is 3 rows of 5 sonotube  piers (12"diam) enough? 

I used the bigfoot approach to mine. I elevated them about 18" off the ground. set the brackets into the cement on the top and bob's you uncle so to speak. (sorry for the Atlantic Canadian term) With the bigfoot tubes they are the only tubes which allow you to back fill around them, then you simple cut open the top on level fill with concrete and good to go.

Quote3 rows of 5 sonotube  piers (12"diam) enough?

I have some correspondence with Bigfoot that I have not yet complied into a concise document. But basically the large diameter pier / footing that they produce do have some impressive lateral resistance numbers.

With 5 constituting a row that's about 7 feet OC. So the next step is to calculate the beam size. That's dependent on what is being supported as well as the distance; how many floors, a loft or full upper, roof with or w/o snow loads.....

Possibly when we get back from TN, VA, WV near the month end I'll knuckle down and find the emails and make some sense of it all. Then post it. Too much going on over the next two days to do it now.

MtnDon,

Was that the info gather by the manufactor of the tubes I used? If so I was wondering how you made out....

Your heading the same route as I did - oh that looks simple cheap and is something I can do myself

the route you should be taking is

What type of soil ground do you have
water level
Frost depth
Wind - direction- strength
Snow load
Stable soil- hill- water run off
Succesfull foundations in your area
Failed designs

These things help in the design of a suitable foundation for your particular plot.

For looking at big foots or post supported structures - you need to start working the loads from the top down

Roof load
Loft load
Floor load

That gives you the total load of the house- more or less

Thats then divided by the beams- depending on wether you have supports in the center of the house- means some load on the middle beam- some loads on the outer walls.
Depending on the roof structure - beams- trusses all distribute the weight diferently, this needs looking at from day 1

The way loads distribute accross a beam is also not linear- some posts will have more weight than others

Once you have the loads traced down - you can then look at what size footing you need and its depth, relative to your soil type

When I calculated mine I found that i needed 36" big foots every 6 feet

Probably cheaper doing a trench, a footing and a block wall and negate all the possible issues with the post and beam.

I have a worked example arround somewhere- I'll have to find it

CC... the short answer is that Bigfoot systems can not supply paperwork that will be sufficient to get building dept code approval for their systems. It's the soil that is the variable that can not be adequately addressed.


UK is onto something. He has found that unfortunately in some locations there is no simple, cheap, DIY foundation method that stands a chance of working. At least he found this before he started his project; he has people on neighboring properties whose homes are trying to migrate downhill. So I guess he is still a lucky soul, luckier than the folks who had issues develop even before their structures were completed.

Re the plan in this thread:  the big unknown is the soil. Have you had a look at the WebSoil survey?  Sometimes that can help and in other locations (like mine) it is of no use. They say to look for local expertise.

I hear ya MtnDon the soil is everything I was lucky in my case I am on 85%+ rock in which I needed a medium duty hitachi excavator zx240-3 in which he had some difficulties. Literally no way I was dugging that up. Fortunately now that he has turned some of it over so to speak it will make it easier in spots where I'l have to dig out underneath for access...