Frost Protected Shallow Foundations

Started by ohio-cabin, August 06, 2005, 11:39:50 AM

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ohio-cabin

Good Day!
Has anybody had experience with Frost Protected Shallow foundations as per NAHB?

http://www.toolbase.org/tertiaryT.asp?DocumentID=2065&CATEGORYID=1093

We are considering it for a 36x32 cabin and find little love from our building department for FPSF. We figure due to lack of experience.
Thanks
Claudia

Amanda_931

I've put a foundation on a footing of gravel over a drain.  But it wasn't the same as the NAHB system.  And no permits.  

Also no problems.  So far, anyway.


tc-vt

I did a FPSF last year in northern VT.  I used more insulation than was recommended for my area and a heated building - more like the required amount for a semi-heated building.  Last winter it went unheated and seemed to be perfectly fine.  I'm going to try to post more about what I have been building.  Most people I spoke with here didn't look upon any kind of slab construction favorably.

Tom

Doug Scheeler

We are going on our second North Dakota winter on a fpsf that we put under a 28x30 1.5story cabin. I researched it very long and hard and have found that it may be better for our harsh freezeing conditions. I feel that with the heat inside the building will help hold the frost from coming under the stemmwall as long as you extend the insulation out from the footing. My first winter was unheated this year will be. No shifting or movment of the footings yet. I work in the dirt business and seen frost as deep as 6-8 feet the right conditions without snow cover. At that rate some basment footings are getting tested. Water lines seem to be fine at the same depth ?? I would not hesitate to build on another Fpsf. 4 foot of Dirt has an R value  equivilant to 1 inch thick pink owens corning polystyrene board. I makes more sense to rely on the board for insulation than just dirt. Hope this helps.   DS

Doug Scheeler

Another thing important is keeping your footing dry. Drain tile ro check out the post on Form aDrain on this forum. Looks to be the ticket for FPSF.  Oh yeah great site John. Thanks DS


glenn kangiser

"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin  http://countryplans.com/smf/index.php?topic=151.0

Please put your area in your sig line so we can assist with location specific answers.

Amanda_931

Yeah, but you're a troglodyte!   ::)

And have a good deal more than 4 or even 8 feet of dirt in a lot of places.

there's a lot of back-and-forth between people who believe in thermal mass and people who believe in insulation.  Each may claim that the other's nuts.

And then there are PAHS and AGS.


John Raabe

Good point Amanda!

Actually the argument between thermal mass and insulation comes down to climate — long term temperature cycles and sun.

Insulation is needed just about everywhere unless you are lucky enough to live on the beach in Hawaii. Otherwise you are going to have some days that are colder than you want and (probably) some that are hotter. Insulation makes it possible for you to afford a comfortable interior climate. The more money you spend on insulation the less you spend on heating and cooling (up to a point).

So where does thermal mass come into play?

Thermal mass is like a bank account for heat. If you have a cheap source of either heating or cooling that you can use in a relatively short period of time then stick it in the thermal bank now and pull it out later.

Thermal mass such as soil is perfect for climates where the average ground temp is close to room temp but the outside air temp goes up and down daily and seasonally. Places like inland California (Glenn  ;)) and the desert SW can fine tune their thermal mass bank accounts with solar inputs. If you're in exactly the right climate and soil temp an uninsulated underground hole will work quite well (the Fresno courtyard underground houses).

Further north folks can still have a thermal bank account but it likely will have to be insulated from the colder soil and, at some point, the solar inputs during the heating season aren't enough to warm it up any more. Poorly insulated thermal mass is always a cold heat sink in such climates (think Irish castle in winter).

That's why super-insulation wins in the cold north.

To confuse the issue a bit, after you have everything inside the well insulated shell, you might still want an extra bit of thermal mass to even out the heating system and perhaps capture a bit of solar gain in the Spring and Fall (these are sun tempered houses).

This is all explained better in the Sunkit...

http://www.countryplans.com/solarkit.htm
None of us are as smart as all of us.

Jochen

 Ah, more from you. Many thanks! What would the world be without a little spam every day!

LoL
Jochen


glenn-k

I got that one, Jochen - they're coming from all over - I guess we must be on a list.

Bouncer

Do you have to follow building codes in your area ? I did shallow On my cabin in Northern Vermont
on post and pier and I just passed my second winter with no problems.
Kevin

glenn-k

What type soil do you have, Kevin, and how deep does it freeze there?

Here we sometimes get a dusting of frost on the ground or maybe a 1/4 inch crust of frost in the dirt- never much more so far.  The valley below 1 mile away is a whole different story.

Bouncer

Glenn the Frost line around here is about 48 inches, but when you get the snow up here it helps insulate things. The deepest hole I had to dig was 12-14 inches.
Kevin

dwolff

What R-value was your insulation and what was the radius of the insulation extending outward from around your piers?


Bouncer

Didn't use insulation once the paver an block were in place I filled the hole with gravel slightly higher than the ground . use silver tarps with a hole cut out for the block extending about 2 feet in all directions from the block then covered with dirt and some more rocks to keep dirt from washing away. So it looks like you have a small mound. It sounds like a lot of work but it goes fast.
Kevin