The “Ask a Builder” series is dedicated to answering some of the many questions Fairbanks residents have about building, energy and the many other parts of home life.
FAIRBANKS — Q: What do I need to be aware of when building on permafrost?
A: Permafrost is loosely defined as soil or rock that remains frozen for more than two 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 simply mean permanently frozen ground or ice is down far enough that the soils can support a larger root system. The only way to be confident of the ground’s content is to have a soils test drilling done.
With permafrost, the safest bet is to avoid building on it altogether and move to another piece of land. This is easier said than done, particularly because of the scarcity of buildable and affordable land near Fairbanks. If you decide to build on permafrost, be as strategic as possible. Smaller and simpler structures tend to fare better than larger, more complicated ones.
The best approach is to minimize ground disturbance. The trees and ground cover are your best friend. They protect and insulate the ground from summer heat. A great example is the green moss found 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 feet, the ground may 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 loss through the floor system from reaching the ground underneath, which can lead to thawing.
In post and pad construction, use a thick gravel pad 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 support the structure and resist frost jacking due to seasonal ground movement.
Cut trees sparingly to maximize site shading (while permitting for a fire break).
Build a wraparound 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.
Hire an engineer familiar with local soil conditions to design a foundation system that will adequately and safely support your home.
Septic systems also must be engineered to function on permafrost, and remember that conventional systems may risk thawing the ground.
For questions or to register for classes, contact the Cold Climate Housing Research Center at email@example.com or 450-1774.
CCHRC is offering a series of classes about building on permafrost:
5:30-7:30 p.m. Nov. 2: Introduction to Permafrost with Kevin Bjella, Cold Regions Research and Engineering Lab
5:30-7:30 p.m. Nov. 16: Permafrost Foundations with Bruno Grunau, CCHRC
Dec. 7, 5:30-7:30 p.m. Dec. 7: Climate Change and Permafrost with Vladimir Romanovsky, University of Alaska Fairbanks
Ask a Builder articles promote home awareness for the Cold Climate Housing Research Center (CCHRC).