BY CCHRC Staff
Energy Focus: Fairbanks Daily News-Miner June 18th, 2009, Section A3
It’s building season. For some, that means finding just the right spot for constructing a home. In Fairbanks, that isn’t so easy. Unlike other places where location, view, and neighbors comprise the major considerations for choosing a building site, Interior Alaska presents a more fundamental question: Will the land itself even support a house? The presence of permafrost can ruin the best laid plans.
Permafrost is just what it sounds like: permanently frozen ground. Permafrost is soil or a combination of soil and rock that remains at or below 32 degrees Fahrenheit year-round. It’s all over the place, but, in the Fairbanks area, tends to be concentrated on north-sloping hills, in shady tree-covered areas, and in lower elevations. Seasonal frost – that crunchy stuff just below the surface of the ground – is not necessarily permafrost. It could just be seasonal frost that thaws in the summer. To make it even more complicated, permafrost is often discontinuous, meaning that it can occur in patches.
The trouble with permafrost comes about when it’s not so permanent. Clearing land of shade trees, excavating for foundations, and the added weight and heat of a house can cause permafrost to melt, setting off a series of destabilizing events that are difficult to manage. Parts or all of a section of ground necessary to support a foundation can shift or sink. These events can cause pipe and drain fittings to break, window and door frames to buckle, and even crack a house in two if not dealt with in time.
What do you do about permafrost? First, you need to know if it exists in the places you want to build. There are old sourdough ways of predicting the presence of permafrost – most of us have been told to be wary of black spruce stands – but the fact is that the only sure way of detecting permafrost is to test for it.
An engineering firm or excavation company will drill the soil and take core samples. These cores will reveal the soil composition, the presence of permafrost at what depths, and if bedrock exists at a certain level. Check with neighbors or existing records, which may testify to the presence of permafrost.
If the core samples show the presence of permafrost, the safest bet is to it avoid it altogether and move on to another piece of land. This is more easily said than done, unfortunately, 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. Minimize any activity that can affect the permafrost. These strategies 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 gravel pads as thick as four to six feet to insulate the ground and spread building loads;
- Building 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;
- 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;
- Installing gutters and manage drainage well away from the house;
These are just some tips to help you start thinking about the very real challenges of building on permafrost and ways to mitigate the risks. In addition to professional advice, a very detailed guide on dealing with permafrost is available for free online. Funded by the Alaska Housing Finance Corporation several years ago, the Design Manual for New Foundations on Permafrost by the Permafrost Technology Foundation is a comprehensive resource online.
Or, call UAF’s Cooperative Extension Service at 474-5211 and browse their online publications.
Energy Focus articles promote energy awareness for the Cooperative Extension Service (CES) and the Cold Climate Housing Research Center (CCHRC). For questions or comments please contact CCHRC at (907) 457-3454