[Strawbale] Frost Heave

[Hank Carr]

Hank Carr wrote:

>> With rubble trench and slab foundations the building should be heated 
>> in the winter whether you are living in it or not to keep the ground 
>> under the building thawed and to prevent heaving and cracking.

Speireag Alden wrote:

> Rubble trench foundations are the whole reason I replied to this 
> thread, since I built my house on one, and they interest me, and your 
> 11/12 remark seemed over-broad to me.

I included grade beams on rubble trenches referring to their slabs, not the
grade beams or rubble trenches themselves.  I did not make that clear.  If
you use a true rubble trench where you remove the organics from the entire
area, dig a perimeter trench, fill it with rubble, then raise the level
under the slab with compacted fill the undisturbed original strata under the
building may be subject to freezing and heaving if the building is not
heated.  It may not be but as I've said it really sucks when they are and it
happens to your house.

I've said many many times on this list and other venues...don't ever accept
as gospel anything that you read or are told by anyone, even me.  Ask a
local expert, your building official, or a local structural engineer what
you can expect from your house or buildng.  If you're planning not to heat
the building for a winter and the area where you live is subject to hard
freezing ask those same people what might happen.  Seeking local advice can
save you a world of misery and it doesn't generally cost you a penny.

> However, my addition incorporates aspects of frost-protected shallow 
> foundations, so they also interest me.

[...]

> Because of those two points, I regard FPSFs which rely on building 
> heat to function as inferior design.

I understand what you are saying.  Most foundation systems, however, rely to
one degree or another on heat escaping through the foundation wall to raise
the frost line.  There are literally tens of thousands of documents
available on the web from governments, engineering firms, universities, and
other sources that explain how foundations work.

>From the atricle "Shallow Foundations" by Robert Koci in the March/April
1999 Home Builder Magazine

-- Ultimately, controlling the temperature is the most reliable
-- way to raise the frost line to accommodate a shallow foundation.
-- It is not as hard as it sounds. The  easiest way to increase
-- the temperature of the soil is to place insulation around the
-- building in such a way that heat generated by the building's
-- heating system is trapped around the foundation wall.

-- The most common method is rigid styrofoam insulation installed
-- horizontally around the outside of the house just above the
-- footings. As the heat from the house tries to escape the house
-- by traveling under and through the foundation wall, the
-- insulation traps it under the soil and stops frost from
-- forming under the foundation.

http://www.legalett.ca/Hmbld99.pdf

>From the booklet "Insulated Slab on Grade Foundations, A Design Guide for
Rural, Northern and First Nations Housing" for the Ontario First Nations
Technical Services Corp. with support from Canada Mortgage and Housing
Corporation by Buchan, Lawton, Parent Ltd. Consulting Engineers

-- Insulation is used to retain the heat immediately adjacent
-- to the foundation which comes from two sources:

-- . heat flowing from inside of the house to the soil beneath
--   and beside the slab; and

-- . geothermal heat from the deep soil - heat stored in the
--   earth below the frost level.

[...]

-- It is assumed that such designs are only to be applied in
-- the following ways:

-- . On heated buildings (it will not adequately protect
--   buildings which are unheated for prolonged periods).

-- . On buildings completed, backfilled and heated before
--   freezing weather occurs.

http://www.fnnhma.com/operations/construction/slab_on_grade.pdf

>From the article "In Cold Ground - Frost Protected Shallow Foundations" by
Elizabeth M. Steiner in Construction Canada Magasine March 2006

-- Frost-protected shallow foundation (FPSF) design provides cold
-- weather durability without excavation below the frost line.
-- Using this technique, a rigid polystyrene (i.e. expanded [EPS]
-- or extruded [XPS]) insulation foam is placed around the outside
-- of a foundation, directing heat loss from the building toward
-- the foundation and taking advantage of natural geothermal
-- energy.

-- It is a design concept that has gained acceptance due to its
-- insulation benefits, energy efficiency, and cost effectiveness.

-- Frost-protected shallow foundations are based on the principal
-- that heat loss through a building's foundation keeps the ground
-- beneath from freezing and heaving by raising the frost depth at
-- the foundation's perimeter. For example, the earth surrounding
-- the foundation of a heated building does not freeze as deep as
-- it would under a cleared road or on a windswept hill. Therefore
-- it is unnecessary to extend the foundation as deep into the
-- ground as for an unheated building. This is especially true for
-- slab-on-grade foundations with slab-edge insulation where the
-- primary path for heat loss is underneath the foundation wall or
-- footing.

http://www.plastifab.com/news_events/articles/shallow_foundations.html

Here's a good document entitled "Frost Protected Shallow Foundation Design
Specifications" prepared for the Minnesota Housing Finance Agency by the
College of Architecture and Landscap Architecture, building Research Group,
L. F. Goldberg, principal investigator.

http://www.buildingfoundation.umn.edu/MHFAfrostFoundation.htm

"Frost-Protected Shallow Foundations" by Bill Eich provides a god
explanation of how the system works.

http://www.countryplans.com/Downloads/shallowfound.pdf

Here's an interesting one...the "Revised Builder's Guide to Frost Protected
Shallow Foundations" from the NAHB (an updated version of one of the
documents I quoted earlier in this thread)

-- A frost protected shallow foundation allows builders to
-- construct a structurally sound foundation that is more resource
-- efficient and less costly than a conventional foundation. The
-- FPSF technology recognizes the thermal interaction of building
-- foundations with the ground. Heat input to the ground from a
-- conditioned building effectively raises the frost depth at the
-- perimeter of the foundation.

-- The effect of heat from the building is magnified when
-- insulation is strategically placed around the foundation. Frost
-- protection of an insulated foundation also works for an
-- unheated building by conserving ground geothermal heat beneath
-- the building. Unheated areas of homes, such as garages, may be
-- constructed in this manner.

http://www.toolbase.org/PDF/DesignGuides/revisedFPSFguide.pdf

>From the "Glossary of buidling science terms used in Homes Across America"
from Resource Efficient Homes Across America, A Showcase of
Resource-Efficient Homes.

-- Frost Protected Shallow Foundations (FPSF) protect foundations
-- against frost damage without the need for excavating below the
-- frost line. A FSPF has insulation placed strategically around
-- the outside of a foundation to direct heat loss from the
-- building toward the foundation, and also to use the earth's
-- natural geothermal energy.

http://www.homes-across-america.org/PDF/HAAGlossary.pdf

>From the brochure "Why You Should Insulate Foundations" from the Dow
building & Construction series.

-- As part of a frost-protected shallow foundation, STYROFOAM
-- extruded polystyrene insulation regulates heat loss and changes
-- the depth of frost penetration into the soil.  This allows a
-- much shallower footing to be used in the foundation. Rigid foam
-- insulation at floor edges and under the slab helps radiant
-- floor heat stay in the building, enhancing comfort and saving
-- energy.

http://www.ilevel.com/literature/179-07771.pdf

>From 99-7 prepared by the Cold Regions Research and Engineering Laboratory
of the United States Army, Lawrence S. Danyluk, March 1997

-- Because of limited resources, a shallow insulated foundation
-- (SIF) was specified instead of a traditional foundation (one in
-- which the bottom of the footing is placed lower than the
-- anticipated depth of frost penetration). In this case, a 20-
-- in.-deep foundation was constructed instead of one at 12 ft. An
-- SIF design allows the footing to be placed at a much shallower
-- depth by incorporating the use of strategically placed
-- insulation around the foundation. The insulation utilizes heat
-- from the building and surrounding soil, redirects it to the
-- area around the foundation, and thus reduces the frost
-- penetration.

http://www.crrel.usace.army.mil/library/specialreports/SR97_07.pdf

>From the article "Building With New Technologies" which appeared in the
summer 2005 edition of the periodical "U.S. Housing Market Conditions"
published by the U. S. Department of Housing and Urban Development

-- Because excavation and concrete are expensive, innovators
-- developed a construction technique called a frost-protected
-- shallow foundation. The technique reduces footing depth by
-- insulating the outer wall. This method allows the home to
-- recapture heat lost through the floor slab and "raises" the
-- frost line, allowing for shallower footings. The use of frost-
-- protected shallow foundation technology enables builders to
-- produce homes with a greater portion of the construction cost
-- dedicated to living space.

http://www.huduser.org/periodicals/ushmc/summer05/article_USHMC_05Q2.pdf

This is just a small sample of the MANY documents which are available.

I hope this helps.

Once again I've provided quotes from the documents along with links to the
original documents so that everyone can read for themselves.  No vague
references.  No broad hyperbole.  Just the facts.

Hank.

"Convictions are more dangerous enemies of truth than lies."
 Friedrich Nietzsche 

"It ain't what you don't know that gets you into trouble. It's what you know
for sure that just ain't so."
Mark Twain