Tag Archives: Permafrost

Shallow Frost Protected Foundations: a good option for the right site

Photo Courtesy Wisdom & Associates. The frost protected shallow foundation uses insulation to create a heat bubble under the structure. The heat bubble keeps the ground underneath and around the structure from freezing, effectively raising the frost depth. The shallower frost depth allows for a shallower footer.

Photo Courtesy Wisdom & Associates. The frost protected shallow foundation uses insulation to create a heat bubble under the structure. The heat bubble keeps the ground underneath and around the structure from freezing, effectively raising the frost depth. The shallower frost depth allows for a shallower footer.

When building homes in cold climates, traditionally the foundation is placed on undisturbed (or compacted) soils and below the frost line to better resist the potentially destructive effects of ground freezing and frost heaving. In Alaska, every region has building codes and/or generally accepted design standards that specify the depth of the local frostline. In Fairbanks, the design depth for footings is a minimum of 42 inches below grade. Installing footings and a foundation wall at this depth can be expensive, and in some cases a shallow frost protected foundation (SFPF) might present a more economical option. As a general rule, a SFPF system is feasible only on ground free of permafrost.

Unlike a standard foundation, a shallow frost protected foundation can be placed well above the frost line — often at depths of about 16 inches below grade, and in some cases less. Since the foundation now rests on soils that normally would freeze seasonally, the key issue is to keep the ground underneath and on the sides of the foundation from freezing. SFPF designs usually depend on foam board insulation laid out far enough horizontally around the perimeter of the footing to ensure that the ground underneath remains thawed year round, no matter how cold it gets.  In essence, the horizontal insulation creates a “heat bubble” in the ground under the building.  A frost protected foundation can accommodate a variety of designs including thickened edge/monolithic slabs and shallow footings.

By code, the horizontal foam board insulation must be protected from sunlight and physical damage. Typically, this means the insulation will get covered with a layer of backfill thick enough to protect it for the life of the structure — although concrete or pavement coverings also might be options (in a high traffic area, for example). Typically, foundations including SFPF systems should extend a minimum of 6 inches above grade to keep wood framing away from ground moisture. Any vertical area above the horizontal insulation also must be well insulated.

In Interior Alaska, SFPF systems are fairly new and a professionally engineered design will buy a lot of peace of mind. Because of site-specific variations in soils conditions and foundation designs, a professional engineer will best be able to calculate the insulation values and installation methods to ensure the foundation will perform properly.

This model is included just to show how heat leaks from the foundation into the ground. “Warm” colors indicate temperatures above freezing. “Cool” colors indicate soil temperatures below freezing. The dashed blue line is the freezing front, which you do not want to contact the foundation.
 

What should I be aware of when building on permafrost?

If pilings are used on permafrost, they must be installed to a depth that will both support the structure and resist frost jacking due to seasonal ground movement.

Permafrost is loosely defined as soil and/or rock that remains frozen for more than two years. In the Fairbanks area, permafrost tends to be discontinuous and is concentrated primarily on north-sloping hills and in lower elevations with heavy ground cover. Big trees do not guarantee the absence of permafrost; it might just mean that permanently frozen ground or ice is down far enough that the soils in that spot can support a larger root system. The only way to be certain of what the ground contains is to have a soils test drilling done.

With permafrost, the safest bet is to it avoid it altogether and move to another piece of land. This is easier said than done, particularly because of the scarcity of buildable land near Fairbanks that is affordable. If you decide to build on permafrost, be as strategic as possible. Smaller and simpler structures will tend to fare better than larger, more complicated ones.

Minimal site disturbance is the accepted practice. The trees and the ground cover are your best friend. They protect and insulate the ground from the heat of the summer. A great example is the green moss you find on many of the shaded low-level areas in Fairbanks. Moss has a high insulating value, and in many cases if you dig down a couple of feet, the ground might still be frozen in the middle of summer.

Strategies for construction on permafrost include:

• As a general rule, the organic layer of ground cover provides insulation and should not be removed, as this will increase the risk of thawing any frozen ground underneath.

• Elevate and properly insulate the bottom of your house to prevent heat losses through the floor system from reaching the ground underneath, which can lead to thawing.

• In post and pad construction, use a thick gravel pad that is significantly wider than the house itself (also insulated if possible) to stabilize the ground and spread building loads.

• If wood or steel piles or helical piers are used, they must be installed to a depth that will both support the structure and resist frost jacking from seasonal ground movement.

• Cut trees sparingly to maximize site shading (while permitting for a fire break).

• Build a wrap-around porch, which will help shade the ground around and underneath the house.

• Incorporate large roof overhangs to shed water away from the house and provide shade.

• Install gutters and manage site drainage well away from the house.

• Retain an engineer familiar with local soils conditions to assist in designing a foundation system that will adequately and safely support your home on the soils specific to your site.

• Septic systems also must be engineered to function on permafrost, and remember that conventional systems might risk thawing the ground.

 

Other Resources 

 

 

 

 

 

 

Permafrost Technology Foundation case studies: http://www.cchrc.org/permafrost-technology-foundation-library

U.S. Permafrost Association website: www.uspermafrost.org/education/PEEP/ptf-manuals.shtml

UAF Cooperative Extension Service online publications at www.uaf.edu/ces.

 

What do I need to be aware of when building on permafrost?

Permafrost is loosely defined as soil and/or rock that remain frozen for more than 2 years.  In the Fairbanks area, permafrost tends to be discontinuous and is primarily concentrated on north-sloping hills, and in lower elevations with heavy ground cover.  Big trees do not guarantee the absence of permafrost, it may also mean that permanently frozen ground or ice is down far enough that the soils in that spot will support a larger root system.  The only way to be certain of what the ground contains is to have a soils test drilling done.

With permafrost, the safest bet is to it avoid it altogether and move on to another piece of land. This is easier said than done, particularly due to the scarcity of buildable land near Fairbanks that can be affordably purchased. If you decide to build on permafrost, do so as strategically as possible. Smaller and simpler structures will tend to fare better than larger more complicated ones.

Minimal site disturbance is the accepted practice.  The trees and the groundcover are your best friend.  They protect and insulate the ground from the heat of the summer.  A great example is the green moss that you find on many of the shaded low-level areas in Fairbanks.  Moss has a high insulating value, and in many cases if, you can dig down a couple of feet the ground may still be frozen in the middle of summer.

Strategies for construction involving permafrost include:

  • Elevating and properly insulating the bottom of your house and all pipes to prevent your house’s heat from reaching the ground with an adjustable post-on-pad system;
  • Using thick gravel pads (also insulated if possible) in order to stabilize the ground and spread building loads;
  • Build using wood or steel piles, or helical piers that anchor in permafrost is an effective, but generally more expensive means of supporting a foundation;
  • Installing thermosyphons to draw heat away from the soil – generally expensive;
  • Avoiding cutting ground-covering vegetation, especially the moss and root layer, that helps to shield the ground from the sun’s heat;
  • Cutting trees sparingly (while permitting for a fire break);
  • Building a wrap-around porch, which will help shade the ground around a house;
  • Incorporate large roof overhangs to shed water away from the house and provide shade.
  • Installing gutters and manage drainage well away from the house;
  • Retain an engineer familiar with local soils conditions

Additional information can be found on the US Permafrost Association website: http://www.uspermafrost.org/education/PEEP/ptf-manuals.shtml the CCHRC library, and UAF’s Cooperative Extension Service (CES) online publications at http://www.uaf.edu/ces.


Newsminer: Scientists meet 25 years later for another look at permafrost

From the Fairbanks Daily Newsminer July 2, 08

From research labs to the big screen, climate change is a hot topic. But in Fairbanks 25 years ago, it was only a theory and one of the six themes explored by the International Conference on Permafrost.

When the conference returned to Fairbanks this week, the subject dominated discussions and presentations.

Click here to read the full article.

Newsminer: Researchers, politicians converge at permafrost conference

From the Fairbanks Daily Newminer June 30, 08

Hundreds of researchers are in Fairbanks this week to get the real dirt on permafrost.

The Ninth International Conference on Permafrost officially began Sunday at the University of Alaska Fairbanks. Held every five years, the conference attracts about 600 participants from more than two dozen countries. The participants will spend the next few days sharing research about permafrost, defined as ground which remains frozen for more than two years.

Click here to read the full article.

9th International Conference on Permafrost

Title: 9th International Conference on Permafrost
Location: UAf Campus
Description: “…summer 2008 represents a special time to celebrate our national and international permafrost heritage. Special efforts will be made to involve young researchers, educators and students of all ages, and native communities from all countries with an interest in permafrost science and engineering.” For more info visit the NICOP website
Start Date: June 29th, 2008
End Date: July 3rd, 2008