Replies

1. 
   DanH | May 06, 2015 08:51pm | #1

   If you go the full 54 inches down and 3 feet up you're looking at 11 courses of 8" block, give or take.

   How much you want to cheat on that is between you and the inspector.

2. 
   MYBuilder | May 06, 2015 09:57pm | #2

   And rookie mathematician

   Sorry, I couldn't resist. The bottom  of the footer should be below frost or 54" in your Area. Depending on the soil composition, local codes, and the size of the cabin, your footer size will be at least 8" maybe more. That brings you to 46". 6 courses get you out of the ground 2". You will want your wood framing to be 8" or more above grade for protection from splash and the occasional major rain event. That gives you 7 courses. That equals 56" to top of footer. I would add granular fill at the bottom of the crawl before the vapor barrier. (The fill allows a marginal amount of ground water in heavy rain events or when the sump pump is not keeping up. That is another thread.) You could add a lot of fill to bring the crawl to only 36", but I would keep it as tall as you can. I like maneuver room down there. As for the freezing inside as the outside does, that depends on the stove,  the insulation, the number of hibernating bears, etc. You would be surprised at the temperature that can be maintained with just the ground heat fro the center of the cabin.

1. 
   Mikalbee | May 06, 2015 11:00pm | #4

   What about frost

   I think Dan H may be right, maybe minus 1 course because of the 8 inch footer. MYBuilder your right, seven courses gets you out of the ground ten inches on the outside, but on the inside it would be only 20 inches to top of footer with my required 3 foot crawl space. Cabin is unoccupied in middle of winter at 40 below. No electric, no sump, I don't think insulation matters and hopefully no bears. Where would heat come from to prevent frost heave?

3. 
   deadnuts | May 06, 2015 10:43pm | #3

   Common sense

   If thermal energy moves from hot to cold, then why does your common sense tell you that "the cold" will be penetrating your seasonally conditoned crawlspace?

1. 
   Mikalbee | May 06, 2015 11:07pm | #5

   Seasonally conditioned?

   I guess I don't quite understand thermal energy when the crawlspace is 40 below in middle of winter.

1. 
   MYBuilder | May 07, 2015 07:35am | #6

   Let's start over

   Your frost depth(per your post) is 54". That means 32 f at 54", not -40. That could be the outside air temp, but not the ground.

   If you dig a hole 54" and add 11 courses your crawl is 88". You would have 36"(roughly with grade variances) of exposed block. Did you need to be 36" out of the ground? Because that practically gives you a basement.

   When you dig a hole 54" and build a structure on it, the heat from the ground will rise out of it. Even if frost is 54" in the ground out side, if you use best practices(why wouldn't you), the ground heat will keep the frost out of the crawl at footer depth. It will not be comfy, just not -40f. Yes, pipes may freeze and your nuts will crawl inside, but no frost heave. If you are 36" out of the ground, you will loose more heat if you don't insulate the block.

4. 
   sapwood | May 07, 2015 11:01am | #7

   I'll offer more confusion

   Frost depth refers to the depth that the ground will freeze to if exposed to normally cold air. If one digs a hole the bottom of the hole becomes the point at which one would start the frost depth measurment. If a structure is built over the hole and said structure isn't heated, the ground will still freeze to the frost depth... sort of. In fact, the system is more complicated but a rigorous analysis would have to be made to determine the true frost depth undrer the unheated structure. 

   What is more important is the quality of the underlying soil. If it's non-frost susceptible, then one can ignore frost depth and build a slab on grade with no problems. 

1. 
   Mikalbee | May 07, 2015 12:44pm | #8

   Confused

   This is precisely why I am confused. I have been researching and talking to builders, blocklayers and excavators for months and everybody has a different opinion for my application, which again is a unheated 24x32 structure during Dec. thru March sub-zero temps. Let me ask this. If this was a vacant house with full basement, concrete floor and no heat during winter sub-zero months, how far do you imagine frost would penetrate below footings? Cabin is being built on highground  in immediate area.                       My soil is : soft topsoil 0-2inches, hard clay 2-18inches, soft gravel 18-39inches, sandy clay 39-60inches and hard clay 60-93in        I thank everyone for their opinions. Maybe I should just dig the hole and build it and not worry so much! 

1. 
   MYBuilder | May 07, 2015 02:00pm | #9

   Totally different question...

   but don't give up. All information is knowledge. In the end, a local, reputable source is your best friend. The physics of building science is still the same. Frost is frozen water. Water expands as it freezes. That creates the effect of frost heave. Houses built on a well drained hill will heave less than houses in a wet low land. If you are building a property to outlast you and yours, spend the money and drain the foundation, put it in low enough, insulate it well, etc. If you want a hunting spot for a get away until you are too old to enjoy it, do the bare minimum and forget it. This is not a condescending post, just opinion. Have you thought of post frame or pier foundations? You could get a very solid below frost footing that way, but the floors would tend to be colder.

1. 
   junkhound | May 07, 2015 07:22pm | #10

   post / frame/ pier

   Yep, that is the way to go.  Since OP says it is a cabin and unheated most of the year, heat loss thru the floor is not a huge economic driver.   

   Own cabin is on posts, has worked well for 35 years.  (note cabin was 'featured' in FHB Nov 1990)

   edit PS: are you going to have water?  Be sure shutoff is draincock type below frost level, and pay close attention to pipe slopes.  PEX preferred (forgot once to drain at my cabin, 3 pipes split).  Half cup of glycol in the sink drain and a cup in the toilet bowl with tank empty - save your old car antifreeze for this.    

1. 
   junkhound | May 07, 2015 07:26pm | #11

   well, guess i shuda said that the shutoff valve is the draining type of 3 way underground valve often described using the same word and spelling as the jobsite word that refers to a swinging appendage? 

2. 
   DanH | May 07, 2015 07:35pm | #12

   Clay is the tricky part of the equation.  Not only does it tend to prevent water drainage, but it's often "expansive", meaning that it expands when wet vs dry (and of course it's doubly bad if it freezes).

   One thing you need to figure out is how you're going to excavate for the foundation.  You can either trench down to footer depth, without excavating any significant amount of soil inside the foundation, or you can excavate the soil inside the foundation, essentially digging a basement. 

   If you trench (and refill after placing the foundation) then a footer at 54 inches is "completely" safe.  If, however, you excavate within the foundation, that excavated depth decreases the frost "safety" of the footing.  Worst case, if the crawl were completely open to the outside, the effective depth of the footer would be decreased by the depth of the excavation.

   There are, as suggested, ways to finnesse this to a degree.  If the crawl is simply enclosed in a more or less "normal" fashion, the frost depth within is probably a foot or two less, even if the structure is not heated.  And one can place insulation near the surface to protect things further.  But all this requires thought by someone knowledgeable in the details.

3. 
   sapwood | May 09, 2015 11:04am | #15

   and the answer is....

   How far will the frost penetrate? You will best find this answer through the efforts of a competent engineer who is versed in heat transfer analysis. That analysis will probably be a bit costly but it'll be the best guess anyone can give you. Otherwise, as I see it you have a couple of choices:

   1. Assume the worst. The frost will penetrate 54" below the surface of your crawlspace floor. So dig a deep trench and stack block. Or, if it were me and I assumed this path, fill the bottom 54" of the trench with non-frost susceptible gravel fill upon which you'd start stacking block.... with a footer. 

   2. Use a pile foundation with insulated floor. If the piles heave a bit you can jack up the structure to re-level it. Simple. 

   3. Keep the building heated. Perhaps the cost of moderate heat will be less than the extra initial cost of total protection.

1. 
   DanH | May 09, 2015 12:36pm | #16

   If the piles go down deep enough they shouldn't heave.

5. 
   deadnuts | May 07, 2015 10:58pm | #13

   FPSF?

   Frost protected shallow foundations (FPSF) have been recognized by the IRC since 2000. Since conventional footings and foundation walls are probably going to be structurally overkill for your cabin, you may want to get familiar with the basics outlined by Mr. Ruiz in this article. With the correct insulation and placement, you could probably save yourself alot of digging and masonry work.

   http://buildipedia.com/aec-pros/construction-materials-and-methods/slabs-for-colder-climates-2-installing-frost-protected-shallow-foundations-for-heated-buildings

1. 
   sapwood | May 09, 2015 10:54am | #14

   I believe that the key work in a FPSF foundation, for this case, is Protected. That protection is provided partly, and not insignificantly, by the internal heat of the building. But the OP's structure will be largly unheated, thus left unprotected. 

1. 
   deadnuts | May 09, 2015 03:16pm | #17

   Not sure what post your are reading, but the OP stated that the cabin will be heated seasonally by a wood stove. I take seasonally to mean winter. You know, like the season when frost can be an issue.

   BTW, vertical insulation is not the only means to mitagate frost heave. Ground heat can be captured by the implementation of additional horizontal insulation.  Thus, depending on the thickness and detailing, source heating from the structure is not that much of a necesssity. In any case,  FPSF's can significatntly reduce the depth necessassary to establish structurally adequate footings.

1. 
   MarkH | May 09, 2015 04:14pm | #18

   Seasonally may be only the season he uses it, which probably is not in the winter, but who knows.

1. 
   deadnuts | May 09, 2015 10:09pm | #19

   Before you totally bury yourself in the hole you're digging MarkH, you might want to think before you type. Seasonally is not a season. YOu also may want to work on your powers of deduction.

   The O.P. clearly stated he plans to heat the strucutre seasonally with a wood stove. Who's feeding the wood stove? The mice? And why would he be heating the structure seasonally? Just a WAG, but perhaps it would otherwise be rather uncomfortable in the winter.

2. 
   MarkH | May 09, 2015 10:34pm | #20

   Keep digging your own hole Dead head. Refer to post #211462 where the original poster says it's unoccupied in winter.

   What about frost (post #211462, reply #5 of 21) by Mikalbee in reply to MYBuilder [original] on Wed, 05/06/2015 - 22:00

   >I think Dan H may be right, maybe minus 1 course because of the 8 inch footer. MYBuilder your right, seven courses gets you out of the ground ten inches on the outside, but on the inside it would be only 20 inches to top of footer with my required 3 foot crawl space. Cabin is unoccupied in middle of winter at 40 below. No electric, no sump, I don't think insulation matters and hopefully no bears. Where would heat come from to prevent frost heave?<

   As for your incorrect statement "Seasonally is not a season.",  you are also wrong.  Seasonal use could occur in winter, but at -40 degrees, I assumed summer use was most likely.  I suppose the owner could have used the cabin during ice fishing season, so assuming... well you obviously know all about assuming.

   Read the definition of SEASONALLY http://www.thefreedictionary.com/seasonally

   sea·son·al

    (sē′zə-nəl)

   adj.

   Relating to, occurring in, or varying with a particular season: seasonal employment.

    

   Let me know if I can help you read and comprehend simple paragraphs in the future. 

3. 
   Mikalbee | May 10, 2015 01:52am | #21

   Simple Question

   Alright fellas, let me try to clear this up. I would agree with this definition of seasonally: characteristic of a particular season of the year. As I said, cabin is not used in the winter. I fish in the spring and hunt in the fall, therefore the only heat this structure absorbs is limited to those seasons. I want to build on block because of the many rodents and varmints in the area. I built an outhouse and sided it with T-111 and the porcupines have had their way with it. Cabin will be metal siding and metal roof. I wanted a 3 foot crawl only to make it easy for the spray foamers to work without cussin me. Can probably get by with 2.5 feet.   Plans are to vapor barrier the dirt crawl to the block wall and then foam either the block wall up to the band joist or just foam the bottom of the floor. Still undecided on that aspect. My question remains, how deep does sub-zero temperture penetrate in an enclosed unheated structure? This is not that big a deal to me to hire an engineer, just looking for an in the ballpark answer.

4. 
   MarkH | May 10, 2015 07:03am | #22

   The frost will penetrate to pretty much the same depth under an unheated structure as it would in an open area.

   As for the outhouse, nothing beats a brick chit house.

5. 
   MarkH | May 10, 2015 07:27am | #23

   Book preview
   I did a search and found this book. You can search the preview sections for frost and foundations, a lot of good info came up. You may want to buy the book, but it is not inexpensive. https://books.google.com/books?id=b6xemxjWPA0C

   Amazon has a used one that is a great deal. ~ $36 http://www.amazon.com/Construction-Cold-Regions-Engineers-Contractors/dp/0471525030

6. 
   mark122 | May 10, 2015 09:29am | #27

   mike your question is so localized. In these parts TVA's studies are showing an average of 60f 22'' down, obviously very different than where you are.

   A good ground source system contractor in your area more than likely knows what your areas avg temps are at certain depths off the top of his head.

   knowing your frost depth(which you do) should be enough to have your foundation planned out. its mighty nice of you to go throught all the trouble just to accommodate the foam guys...

7. 
   deadnuts | May 10, 2015 09:09am | #25

   Okay. I'll spell it out for you. Winter, Spring, Summer, and Spring are seasons. Let me know when you find documentation (other than your imagination) that seasonally is considered a season.

   Where does the heat come from? The earth.  Read up (something other than your comic books woudl be a good start) on FPSF's sometime.

   I'll give you a little hint of what you'll find. This from Bill Eich in JLC way back in 1996:

   "The technique’s success is based on a fundamental principle of physics: In conductive heat transfer, heat travels from warm to cold, and it will always follow the path of least resis-

   tance (see Figure 1). The earth generates its own heat. In a deep frost footing, the soil around the foundation (along with snow cover) stores the heat and slows its movement from within the earth, keeping the deep subsoil warmer than freez-ing year-round. In an FPS foundation, well-placed foam insulation provides resistance that directs the heat flow under theshallow footings, where the soil, with its high heat-storage capacity, stays above the freezing point year-round."

8. 
   MarkH | May 10, 2015 09:29am | #26

   Read the definition of SEASONALLY http://www.thefreedictionary.com/seasonally

   sea·son·al

   (sē′zə-nəl)

   adj.

   Relating to, occurring in, or varying with a particular season: seasonal employment.

   Let me know if I can help you read and comprehend simple paragraphs in the future.

   You just don't get it.

9. 
   MYBuilder | May 10, 2015 09:40am | #28

   I can't seem to find that Sesame Street episode, but I'm sure there was a fall season when I was a kid.

10. 
    deadnuts | May 10, 2015 10:43am | #29

    MYBuilder. I left that out as a test for MarkH. Unfortunately, he's still as clueless as ever. YOu, however, seem to be getting the hang of the concept There's hope for you yet.

11. 
    MarkH | May 10, 2015 02:23pm | #32

    Tornado season is upon us. http://www.climatecentral.org/news/tornado-season-shifting-earlier-in-tornado-alley-18073?gclid=CjwKEAjwg7yqBRCu5NmlgMm6i08SJADDEudZvb_Stg6K-Swtv96UuwATsCMCztrQblwIbo4K3VfDehoCKyPw_wcB

    Allergy season is already here too. http://www.mlive.com/weather/index.ssf/2015/05/allergy_season_in_michigan_bei.html

    Hurricanes occur seasonally as well.

    And I understand that seasonally is not a season, and never I never said it was.  Seasonally means something occuring during parts of a year, not continuously.

    You really aren't nearly as smart as you think you are. 

12. 
    deadnuts | May 10, 2015 11:15am | #30

    Now you've descended into

    a state of denial.  Do you really want to be going there? It's not particularly productive for you.

    MarkH wrote:

    And I understand that seasonally is not a season, and never I never said it was. 

     Post# 211462:    

    "Seasonally may be only the season he uses it"  Mark H.

13. 
    sapwood | May 10, 2015 11:23am | #31

    Don't forget that there is the "Season to be Jolly...."

6. 
   MYBuilder | May 10, 2015 08:13am | #24

   Dirt has Rvalues .25-1 with a typical .8 at 20% moisture. Obviously differences are due to soil composition. With 54" of dirt at worst case R.25 with you have R 13.5. If you are using spray foam and are going with the prescribed Rvalues for zone 7, R27 wall plus cavity and R60 roof, you will have more insulation Rvalue than the soils outside. The ground source heat will keep out the frost if the insulation goes down to the footer and the insulator will love a 54" crawl.