Insulating your septic tank; identifying permafrost; putting up a wind turbine

Alaska HomeWise: Ask a Builder

By Cold Climate Housing Research Center Staff

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.

Recently, I was scoffed at for wanting to insulate my septic tank when I install it next summer. How much insulation is necessary for a septic tank?

Septic tanks contain bacteria that will break down septic sludge. These organisms will do much better in a warm environment than a cold one. There is some debate on how much insulation makes a difference when it comes to soil temperature and bacteria performance. However, a bigger concern is a septic tank freezing because it was not buried deep enough, or does not have enough insulation to protect it from cold air. A frozen septic is more likely in the winters of extreme cold with little snow. In that case, the ground freezes very hard and very deep.

When in doubt, it is cheap insurance to add a layer of rigid two-inch foam insulation on top of the tank and a few feet down on the sides. In fact, insulating a septic tank is a good way to use up all the damaged or left over pieces of foam from a jobsite. Another alternative is to have the top of the tank sprayed with several inches of polyurethane foam. Do not forget to consult with the Alaska Department of Environmental Conservation for the most recent codes for insulating a tank.

Is there a way to tell if land is full of permafrost just by looking at it?

There are some visual indicators, but they are not 100% reliable when determining whether or not land has permafrost. For starters, look at the other houses in the area and the types of foundations they have. If there are a lot of houses on posts, or if houses with conventional foundations are sagging, that could be a sign of permafrost. If the land is down in the flats or on the north side of a hill and has mostly little black spruce trees and moss, that often indicates ice in the soil, because the land cannot support a big root structure. Sometimes a piece of land can have good-looking ground but permafrost underneath at a low depth or ice lenses (pockets of ice) only under small areas.

Not everywhere has a lot of wind, so when is putting up a wind turbine system practical? ?

You can still put up a turbine, but it is important to have a good wind resource. If you are connected to the electrical grid, you want to have average wind speed at about ten miles per hour or better. Of course the cost of electricity for your home will dramatically affect any possible payback of putting in a wind system. If you are in a village and paying 60 cents a kilowatt hour for power, then having “enough’” wind is going to be different than if you are in Anchorage and paying eight cents a kilowatt hour for power. Look at how much energy you are likely to produce annually, how much money you will save, and the cost of installing a system – all before deciding if a wind system is cost-effective.

Alaska HomeWise articles promote home awareness for the Cold Climate Housing Research Center (CCHRC). If you have a question, e-mail us at You can also call the CCHRC at (907) 457-3454.

One comment

  1. Recently, I was scoffed at for wanting to insulate my septic tank when I install it next summer. How much insulation is necessary for a septic tank?

    An interesting point! The bacteria in a septic work best at 95f.
    That is converting our toilet into carbon dioxide, methane and other gases, the more converted, the less compost remaining, the longer the time between costs of emptying.
    The colder the ground, the slower the bacteria work, the quicker the build up, septics down in Florida work so much better, all other things being equal.
    If you are going to do it, go for six inches and remember the sides are in contact with the ground as well. Heat from the bacteria moves sideways and down into the ground as well as up.
    With most septic systems, the build up comes over winter, followed by grater activity during the summer, most septics empty a few inches over the summer.

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