Building on Permafrost
Changing climate is just another challenge for builders keeping it cool in the Arctic
The ASRC Vehicle Maintenance Shop in Deadhorse was designed with thermosiphon condenser risers.
When constructing in the Arctic or near-Arctic regions of the world where permafrost dominates, the adage “If it’s frozen, keep it frozen; if it’s thawed keep it thawed” provides a strong foundation. Doing this, however, is one of the greatest challenges for engineers and construction companies that specialize in building in some of the coldest places on Earth.
“The design of the foundation, which is the interface between permafrost and the building, can be directly related to the success of or failure of a building on frozen ground,” explains Bruno C. Grunau, chief programs officer at the Cold Climate Housing Research Center (CCHRC). CCHRC is an industry-based, private, nonprofit corporation with the mission to promote and advance the development of healthy, durable, and sustainable shelter for Alaskans and other circumpolar people. “Once the permafrost thaws, the foundation can sink, damaging the building it supports. The key to successfully building on frozen ground in the North is to maintain a near-constant subsurface thermal regime where the foundation bears on the soil.”
A poorly designed or poorly maintained heated structure can be the catalyst for repeated thawing and freezing cycles of the ground, causing it to heave, slough, and even creep—usually to the detriment of the building.
“There are a myriad of things to consider when looking at a project on permafrost. I always first consider the importance of the project and the consequences of a failure,” Arctic Foundations President Ed Yarmak says. “And then, of course, there’s the budget, which turns into the usual constraint for many public projects. Budget and service life are the main drivers. Sometimes there’s trade-offs… and service life is compromised.”
An early step in the design process of a project is to get good site data. Ideally, a team would be able to obtain the vertical temperature distribution down into the permafrost over the course of a year.
“We hardly ever get that data because of schedules or budgets,” Yarmak says. “Engineers can make estimates, but then, that’s just another uncertainty in the design that needs to be taken into account.”
What data they are able to collect allows a team to—among other things—determine if the site is thaw stable, which is generally a factor of how much ice is in the permafrost material.
“If it is thaw stable, then standard construction techniques utilized for non-permafrost sites in cold regions can generally be used,” Yarmak says. “If it is not thaw stable, then engineers either design the structure using specialized materials and construction techniques to keep the heat balance negative or build the structure in a way that it can be maintained as the permafrost thaws and settles.”
Though many think of permafrost as permanently frozen soil, it can be more broadly defined as any earth materials (granite bedrock in the mountains to silty soil on the Tundra) that remain below 32 degrees Fahrenheit for at least two consecutive years.
These back-to-back years of freezing temperatures are caused by a negative heat balance, meaning that more heat leaves the ground during the winter than is absorbed via geothermal heating and the summer sun. Two years, of course, is just a minimum requirement. Some of the permafrost in Alaska has been around since the Pleistocene Epoch (during which the Ice Age occurred), which is why there are areas on the North Slope where it’s 2,000 feet thick.
“The ground surface will freeze and thaw every year over permafrost. That zone of surface freeze-thaw is the active layer,” Yarmak explains. “When the winter cooling is not sufficient to freeze the active layer to the top of the permafrost, a talik [a layer of unfrozen ground in a permafrost area] will be formed between the base of the active layer and the top of permafrost. Existence of a talik like this is generally an indicator that the heat balance has moved from negative to positive and that the permafrost is degrading.”
The degradation of permafrost can happen both through climate warming and the construction of man-made structures on top of it. However, Arctic engineers have a number of methods to prevent permafrost from thawing below buildings.
Fairweather Deadhorse Aviation Center, built on permafrost, is a multi-use facility with offices, room and board, incident command center, and hangar and serves as CPAI Shared Services Airline Terminal.
Active and Passive Temp Control
“There are many approaches to designing and building in a permafrost location,” Principal Architect for Architects Alaska Michael Henricks says. “Depending on functional, scheduling, and budgetary requirements for a project, one may employ a combination of approaches, almost all of them passive in their methods for keeping a structure’s heat out of the ground.”
Passive approaches do not rely on electricity; they function either by elevating the structure above ground or through the use of refrigeration systems that employ fluids that have physical properties that change from liquid to gas at temperatures above and below 32 degrees, Henricks explains. As the gas rises, it releases heat above ground. As it does so, the gas condenses into a liquid, which falls back to the bottom of the system, where it again can collect heat, expand, and rise to release heat above the surface.
The two primary forms of passive cooling systems are thermopiles (heat-syphoning stilts) and thermosyphons.
“Thermosyphons are long, sealed tubes that are installed into the ground beneath the structure and the top is exposed to the cold winter air,” Grunau explains. “A phase changing substance within the pipe pulls the heat from the ground and releases it into the cold winter air. This system has no moving parts and requires no power to operate.”
Whether thermopiles or thermosyphons are used in a project is the result of many factors, including functional requirements of the building.
If stairs or ramps are going to hamper a building’s function, designers are forced to rule out using thermopiles, using thermosyphons instead. Thermosyphons are also preferred for buildings with a heavy floor load, since a slab-on-grade system is generally more economic than a structurally supported floor.
“On permafrost, a slab-on-grade with a system of non-frost susceptible gravel, insulation, and Thermoprobes (our trade name for non-load bearing thermosyphons) is usually more economic than a pile supported structural floor,” Yarmak says. “It’s also a bit more convenient to drive into compared with pile supported structures. If there is no non-frost susceptible gravel available, then the economics may change.”
However, if the goal is to have the least impact on the landscape, leaving it in its natural state, piles or thermopiles are the best option, Henricks explains.
“One wouldn’t want to bury the landscape surrounding the structure under a gravel pad if that is the driving force of the design,” Henricks says. “Residential related projects may often want to take this approach or eco-tourism lodges and the like.”
Piles and thermopiles remain the most popular way to prevent thawing. Simple piling structures provide a certain level of protection to permafrost as they create a separation between the heat source and the frozen ground, providing a shadowing effect on the ground below the building and helping to block ground insulating snow from building up on the ground beneath, which leaves it exposed to extreme cold winter temperatures.
“Erv Long, working for the US Army Corp of Engineers, developed the thermopile in the 1960s,” Henricks says. The thermopile is a passively refrigerated piling system that combines a pile foundation approach with passive refrigeration technology, enabling a thermal transfer process action to draw heat from the ground surrounding the pile.
“There are now more than 900 installations of this and similar technological approaches in use today, and many more in design as we speak,” Henricks says. “Today, companies such as Arctic Foundations offer a variety of configurations of passive refrigeration technology approaches for the foundation design of structures over permafrost.”
Though the thermopile isn’t exactly new technology, Yarmak points out that Arctic Foundations’ products are improved and that the company’s product line is currently larger than any other thermosyphon manufacturer in the world.
“These devices are used to ensure a negative heat balance in the permafrost, thus keeping it from warming and losing strength,” Yarmak says. “Typically, insulation is also used to minimize the heat gain into the permafrost, but not always. We believe that there will be an increase in the need for thermosyphons as the climate warms.”
Yarmak notes that the company is also seeing more applications for adding active refrigeration capabilities to passive thermosyphons to reduce thermal impact on the permafrost and accelerate construction.
Ground source heat pump technology is also rapidly expanding and becoming more and more efficient.
“In this situation, one would install several hundred feet of plastic piping beneath a foundation,” Grunau explains. “A ground source heat pump circulates a fluid through those pipes and uses a refrigeration process to pull heat from the fluid and deposit that heat to the building as a heat source. “
Another factor considered when preserving permafrost is a construction company’s approach to ground disturbance, as the natural state of the ground helps to protect permafrost.
“It’s difficult for some to understand that this material [permafrost] that seems to be as hard as concrete or stone is as fragile as a ripe peach on the surface,” Yarmak says. “And surface disturbance can lead to much more than just eyesores—it can cause permafrost degradation, erosion, thaw slumps, and a multitude of other issues that can come back to cause problems with the structure.”
Whether it is desirable or necessary to build a compacted gravel pad over undisturbed ground surface is really a question of a building’s function or structural requirements and if the project owner wants the building site to be left in as much of a natural state as possible, Henricks notes.
Though the right foundation is essential to building in Arctic and near-Arctic regions, there are two other major challenges to rural housing in the coldest parts of the world: ventilation and heating.
“When it comes to saving money [and energy] to heat your home, the most cost effective approaches are generally increasing insulation in the building envelope and tightening the building envelope by air-sealing,” Grunau says. “At the same time, having a functioning ventilation system is critical to the health and safety of the occupants, as well as the well-being of the building structure.”
In homes with high humidity, moisture can condense on walls and create and environment for mold to grow. This mold can affect the respiratory health of families living in that home. Additionally, some molds can cause rot, which could undermine the strength of the building structure, he says.
The best way to alleviate poor indoor air quality is to dilute indoor air with cleaner outside air.
“Experts suggest changing the air inside your home on a regular basis, between one-third to one-half complete air changes per hour. That means moving all the air out of your house and replacing it with outside air every 2 to 3 hours. Often houses do this in the form of a bathroom fan, range hood, or heat recovery ventilator,” Grunau says.
To help address both issues—high energy costs and poor ventilation—CCHRC developed the BrHEAThe system in 2011.
“BrHEAThe combines heating and ventilation into one distribution system to provide fresh air and space heating to homes,” Grunau says. “Since development, it has been installed in homes in Anaktuvuk Pass, Fairbanks, Galena, Buckland, Point Lay, Brevig Mission, Minto, Bethel, and Tanana.”
Aerial view of the Fairweather Deadhorse Aviation Center, built on permafrost.
The challenges of construction in the north will continue to grow with the increasing effects of climate change.
“The climate has been shown by scientists to be changing, becoming warmer—a situation that also has been observed by indigenous people living continuously in Arctic climates and deeply attuned to the environment,” Henricks says. “The planet is getting warmer, and thus permafrost regions are being impacted greatly.”
Some structures built over permafrost decades ago, even elevated on traditional piles, are failing due to the warming climate, Henricks notes.
However, not all degraded structures built on permafrost are victims of warming, many have simply outlived their design life, not been maintained properly, or were not designed properly, Yarmak points out. Nonetheless, Yarmak recognizes rapid changes in the Arctic.
“With climate warming, the access road that was put in thirty years ago may not be suited for another thirty years of service. Things change, and they change rapidly when ice melts because water has no shear strength. More ponded water in low places absorbs more heat in summer and adds to the heat balance,” Yarmak says.
In many places the increased heat is not enough to shift the balance of the permafrost, but it will increase the depth of the active layer, and if there was ice-rich material at the base of the active layer, there will be surface subsidence.
“That soils investigation that was performed twenty-five years ago may not be valid for a new design at the site because of increased ground temperatures, perhaps the formation of a talik, or other issues. The active layer is going to be deeper because of the warmer temperatures,” Yarmak says, noting that on sloped sites with an active layer increasing in thickness there is greater possibility for development of an active layer detachment slide.
Compounding the issue is that engineers are struggling to get accurate estimates of what the climate will be like in twenty-five to thirty-five years as global warming rapidly increases.
“We can use estimates from the climate modelers for this, but there is a huge variability in what the various models say,” Yarmak says. “Still, it’s better than a crystal ball. And then, there’s the weather.”
Without a doubt, one way that climate change will impact Arctic construction is that it will drive up costs.
“Piles need to be deeper or larger in diameter, insulation needs to be thicker or over a larger area, gravel pads and roadways need to be more robust, and the ice road season for tundra work will get shorter,” Yarmak says.
However, where there is change is there is a chance for growth, development, and innovation.
“The flip side is that climate change offers economic opportunity to companies such as Arctic Foundations,” Henricks points out.
Isaac Stone Simonelli is a freelance journalist and former managing editor for the Phuket Gazette.