Need help with small cabin foundation choices

[nasmeyer]

I am considering building a small 9'x16' cabin (144 sq feet is under the limit for a required permit) which will likely have a 12' roof line to accommodate a small loft, for hunting and occasional use a few times per year on my property in northern Michigan. I was thinking of using sonotubes for piers, which would support two 16 foot girders/beams (9 feet apart) that would be the support for my 9x16 2x8 and plywood deck and cabin. This is where I have a couple of questions someone may be able to help me with.

(1) I have seen many postings on-line where people used pre-cast pier blocks in cold climates, and I have read posts where people used poured concrete piers like Sonotubes, what are my advantages and disadvantages to using either method? wouldn't a small building like my plan with a tall roofline be susceptible to movement with high winds if I used the precast method? What about frost heave?

(2) I am in very sandy soil, and Michigan has a 42" frost depth, since sand drains well do I still need to go below 42" for my sonotube piers? Would I need a paver or footer under the sonotubes or just the tube itself? I am also on the top of a small hill so I have good drainage.

(3) What size beam/girder would I have to build/use to span 16 feet between piers, and support my small cabin? I would like to get by with only 4 piers, one in each corner (this would limit my number of holes to dig, and amount of concrete and water to transport since I am in a remote location). I found a chart that seems to show me I could span 16 feet by sandwiching three 2x12' together for each 16 foot beam. Could I cantilever my piers inward on my 16' beams so I am only spanning 12 to 14 feet, or is this not a good idea? 

Thanks in advance for any help or ideas.

[glenn kangiser]

  to the forum.

1.  Either of the two choices you poted would not be as good as bigfoot footings at resisting uplift but I wold say Sonotubes from below the frost line would be second best.

2.  Sand could be pretty good, but there is a time when capillary action slows the drainage of the sand leaving the possibility of frost heave.  Probably better to be safe.

3.  I think cantilevering could work for this small cabin but I am not an architect or engineer.  It seems to me that there would still be too much weight for 4 piers unless you made them extra large - maybe a couple square feet or more each - est 14400 lbs load depending on snow and if my rough guesses are correct.   

[MountainDon]

  nasmeyer

I have a question/comment. 9 x 16?   10 x 14  is basically the same square footage for all intents and purposes, and might make better use of standard size building materials. 

I believe that span would be stretching things for only four piers. Six may be better.

Have you looked at John's Little House plan set? In includes a 10 x 14 version. It uses 6 piers with two 4x6 beams spanning each set of three.

By 12 ft roof line, do you mean a 12 foot tall wall height, measure outside?    That's seems very tall for such a small footprint. I would want something like that anchored very well, rather than simply sitting on top of pre-cast blocks.

And just by way of curiosity how would such an obvious upstairs be looked upon by the code official. Does it become living space and add to that 144 sq. ft. Different folks could interpret that... differently. 

Anyhowe good to see ya'. Don't be a stranger.

[Rover]

Nasmeyer,
glad you are asking the question.  I'm in the same boat.  I'll be building a 108sf 'tool shed' this Spring. Its the max size to avoid needing a Building Permit.  I have to call it a 'tool shed' because that is the only structure the Bylaws permit.  No loft space.

Be careful with the loft.  You don't want someone to consider that as floor area.

I'm building in Ontario and likely need the same frost protection.  I'm thinking of digging down 2' or so to get good bearing.  Then sit a thick patio slab down as the footing.  (I got these slabs from a construction site.  The guys who set up office trailers, use them as pads.  They are 18" x 18" x 4" thick.)  Then build cast in place piers from sono tubes.  I'll protect the footings from frost by laying down SM boards around the piers.  1" of SM = 1' of dirt for frost protection.  The insulation boards also have to extend outward so frost can't travel horizontally to get below the footings.  Carrying in SM boards is easier than digging deeper.

Those are my thoughts, but I don't have any experience with small building construction.

[nasmeyer]

nasmeyer

I have a question/comment. 9 x 16?   10 x 14  is basically the same square footage for all intents and purposes, and might make better use of standard size building materials. 

By 12 ft roof line, do you mean a 12 foot tall wall height, measure outside?    That's seems very tall for such a small footprint. I would want something like that anchored very well, rather than simply sitting on top of pre-cast blocks.

And just by way of curiosity how would such an obvious upstairs be looked upon by the code official. Does it become living space and add to that 144 sq. ft. Different folks could interpret that... differently. 

Thanks for the reply MountainDon, I am not set on the size of 9x16 yet, but was interested because of the wall  dimensions of my 9x16 plan. I found a plan here http://www.minicabinplans.com/ for a similar cabin/shed but would like to increase mine to 144sq feet. It would have a mono-pitch roof or "lean-to" style roof, with a 12' front wall and an 8' rear wall which would allow me to install windows along the top edge of the 12' wall which would face south, and bring in lots of sunlight, also allowing for some loft space. This design would also give me an open feeling inside with the high wall on the south side. Do you think loft space in this style building would be considered floor space? This is also why I was concerned about some type of anchoring, a 12x16 wall could pick up some wind. The roof span would be roughly 10' which would allow me to use 12' metal panels and create a 1' overhang at each wall. I am open to other sized deck plans but really liked this idea for the sunlight coming in along the top of my south wall.

[MountainDon]

Do you think loft space in this style building would be considered floor space?

It depends on the way the inspector/county officials look at it.     There can be a lot of leeway/discretion afforded to inspectors. And sometimes not.

Jurisdictions allow storage sheds up to a certain size without permits all the time, but may draw the line at any pretense to be or not to be for human habitation.

Depending on your own thoughts, how close the neighbors are, are they good neighbors, how visible your place is from the road, etc. , some people just do it.

[nasmeyer]

nasmeyer


Have you looked at John's Little House plan set? In includes a 10 x 14 version. It uses 6 piers with two 4x6 beams spanning each set of three.

No I haven't seen John's plan, since I am new here please send me in the right direction with a link, I would like to see it.

[glenn kangiser]

Here are the Little House Plans http://www.jshow.com/y2k/listings/29.html

and more here.

http://www.countryplans.com/plans.html

[nasmeyer]

Thanks for the help on my post. Anyone have any positive or negative comments about this style cabin I found plans for here? http://www.minicabinplans.com/ does the roof pitch look like it will work in a snowy climate?

From the replies above it would seem I will need to go with 6 piers, especially if I stretch this plan to 10x14. Again thanks for the help, and any more comments would be welcome.

[MountainDon]

Choice of roof for snowy climate involves several factors. The amount of snow, the size of materials used for framing the roof, and the roofing material to some extent. Metal roofing sheds snow much more readily than shingles, for example. The pitch does enter into it, but I believe it's only if it's a low pitch, less than 4:12 when it becomes a concern... that is snow will not slide off those lower pitches. Those are the roofs you hear about caving in.

Do you know what the snow load is for your area? Depending on where you are going to build that info may be readily available from the local building permit department. Armed with that and the width of the building it's a matter of simple calculations or using a chart or rafter calculator.

ED: A quick look at the IRC snow map shows 50 to 70 psf ground snow loads for northern Michigan.
50 psf would need at least 2x8, #2 DF or SPF
60 to 70 psf.... 2x10,  all at 24" OC
Sizes could be reduced with closer spacing.

A peaked roof could use smaller sizes as long as everything else remains the same.

[Woodsrule]

  Nasmeyer,

I built a 10x14 mini-cabin three years ago on the side of a hill (1000 feet elevation) in New Hampshire. I went with 9 Bigfoot and sonotube combinations and used a double rim joist and 2x6 floor joists.  Since I used so many piers, the 2x6s are more than sufficient.  Also, I went with a 10 pitch roof and 8 foot sidewalls, giving me good head room in the lofts at either end.  As a result, we can sleep five people very comfortably and the 10x14 design allowed us to efficiently use standard lumber.  We took pictures of each step, so if you want to see them, let me know and I can e-mail them to you.  Welcome to the forum and good luck to you.  Tony

[nasmeyer]

Thanks for the reply Woodsrule I would like to see your pics and have sent you my e-mail addy. I would still like to limit my sonotube number and use a stronger beam/joist combination if possible, but 10x14 sounds like a better size and use of lumber than my earlier idea. Did you use a plan or build from scratch?

[Woodsrule]

We built from scratch; previously, we had built a storage shed at our home property (12x16) and we just beefed up the foundation specs and used 8 foot side walls for a bigger loft area. I will send you the pics asap, but I didn't get you address.  Let me know yours and I will send those right out.

[MountainDon]

Woodsrule. nasmeyer's email address is right there on the left, under his name (by any message he authored.) Also on his profile page.

If you want, why don't you post the pictures here; this thread or make your own topic?? I'm sure there may be others who'd be interested.

[nasmeyer]

Hi Woodsrule, my addy is nasmeyer@hotmail.com you contact me here and I will forward you my high speed addy for the pics. Thanks.

[kev_alaska]

We built the 10 x 14 little house directly from John's plans here. Six pier blocks setting on paver stones. Soil is sandy with clay underlayment. We chose the 12/12 pitch roof option for a loft. Third winter in it with snow conditions on the high end of the scale.

We are building a bigger one just into the woods from this starter. With the exception of some first winter settling of the piers (we adjusted them with the brackets) the little house has been solid as a rock.

[StewB]

Kev, how much snow did you get?  I'm building the 12x18 little house with a 12/12 roof in a location that can get 6+ feet of wet snow.  I expect the 12/12 roof will shed snow long before it gets to heavy.

[considerations]

There is so much info out there about foundations that data overload is quite possible..

I'm on the Olympic Peninsula in Washington state...a few miles from the rainforest.  The soil I'm on is about 3 feet of clay with organic material, then comes the sticky peanut butter clay.  The boundary between the two is where water collects. 

The weather here is temperate....a ridiculous high is over 90 F and rare, a ridiculous low is 17 F also rare.....(good thing).  The average rainfall is about 45-50 inches, starts in October, off and on till April, unless it's snowing.  Deepest snow I've seen in 3 years is about 2 feet...lasted for about 2 weeks.   Mostly it is about 40 -60 F. 

We do get tremblers 2 - 4 Richter scale, with a good jolt every couple years 5-7 Richter scale.  I'm not worried about the world ending, I just dont want to put all that work into this sweet little house (14 x 24) and have the foundation dump it on the ground.   

There are lots of places around here that have been standing for 80 or more years with no foundations at all...so its my ignorance, not my angst talking.

[John Raabe]

I know your climate well  .

We do have earthquake considerations to deal with and most small buildings with modern post and pier foundations will do just as well as a house with a perimeter foundation. You do want to strap the piers to the beams and the walls to the roof. That and the structural sheathing I call out in the plans will keep the place together for the expected tremors we will likely see over the life of the building.

If we have the REALLY BIG one, where the ground drops 9' in one shot (as it seems to have done in the 1600's) well, just hold your breath and cover your head.

Because we don't have deep soil freezes, the wet clay soil is not as likely to cause uplift as it would in the NE states or eastern Canada. Still, the better you can drain the footings the more stable your foundation will be. (This is important for both pier and perimeter concrete wall footings)

[considerations]

Bless your heart for such a quick answer.  May I please ask you how to show my location in the profiles?  I've tried a couple things, and I'm missing the obvious, I'm sure.

[John Raabe]

Click on your Profile in the blue menu at the top of the forum page, go to Summary, and see the Location box where you can type whatever you want.

[considerations]

You're gonna hate this...I did, its in there.  Sorry

[MountainDon]

Follow this link.

http://countryplans.com/smf/index.php?topic=3590.0

the third image down shows the field "Personal Text"

Lots of other help in the Forum News board

http://countryplans.com/smf/index.php?board=7.0

[considerations]

Got it, thanks...its working now in the personal line.

[Redoverfarm]

Is considerations for a he or she?  Takes some time to get it all fine tuned.  But you are in the right vacinity.