For me, it was dahlia tubers and cabbages. For some people it is home canned food or maybe their pet’s comfort or a winter workshop. I needed to insulate my garage against the pending sub-freezing temperatures. I needed to get it done rather quickly.

In the heat and busyness of summer, it can be hard to remember how cold a garage can get in northern climates. While it is true that a garage can on average stay 10 – 12°F (6 – 7°C) warmer than the outside temperature, this should not be assumed if there is anything at risk. It will depend on factors such as whether or not the garage is adjacent to the house, has windows, and how well the doors close.

For instance, my garage has finished walls, but the main door, the big one that opens to let in the occasional vehicle, is one of the oldest automatic garage doors in Idaho. It is a single layer of metal that rarely closes all the way. Thus, it conducts heat whichever direction quite easily and provides uncontrolled ventilation.

My garage also has several windows, which is great for light, but they are single pane. The larger ones are positioned on a tree shaded, northeast exposure, so are not providing much solar heating. There are two pedestrian doors to the outdoors which have a couple of the windows I spoke of. These are much less substantial than the walls and they don’t fit all that well. The last anti-insulation factor is the broken cat door, which is in one of these outside doors. It is only about 6 by 6 inches, but it is a funnel for a strong wind.

On the other hand, I have a couple of unusual advantages. The back wall of my garage is partially insulated by the equipment housing for my swimming pool. Since the pool is heated all year long, this provides some heat to the garage as well. Another good reason to put that swimming pool in next year that you’ve been thinking about.

Lastly, there are a couple of closets with sliding wood doors, on two different walls of the garage. Not only do these provide a layer of insulation, particularly if we keep them closed, but the closet next to the house wall can be it’s own little micro-environment. The mice agree.

The quick fix for keeping my garage warm was both macro and micro. On the macro side, I put bubble wrap up on all the larger windows. This necessitated cleaning them first. At first, I was grossed out by all the cobwebs, but then I saw that they had really done their job catching undesirable flying insects, so I adjusted my attitude.


I know how well bubble wrap works because we have used it in my greenhouse for a few years now. The instant it is applied to the windows, the connected kitchen area in the house is incredibly warmer. My husband purchased it locally at Dixon Container in Boise in a large roll, of which there was plenty leftover for this job. Quick tip: use a spray bottle to wet the window glass before gently pressing into place the piece of bubble wrap that has been cut to fit the dimensions of the window.


Since we still have a cat, we didn’t want to just plug the cat door. The cat sleeps inside with her girl part of the night, but often decides to go prowl at about 3 A.M. So, my husband taped some yellow caution tape in strips from the top of the defunct cat door opening. It looks like the entrance to a cat warehouse now. Or a warning for the mice, which she has been catching this week, thankfully!


Other macro changes are being planned, such as a new and insulated garage door. New pedestrian doors may have to wait longer. I may consider putting up hooks to hang some quilts or carpet scraps over the windows, for one more layer of insulation.

Meanwhile, for the dahlia tubers, which are supposed to be kept between 40 and 50°F for the winter, I worked on micro level insulation in one of the closets next to a wall of the main house. To be sure, it was not an empty closet, but the animal food was temporarily relocated. That should confuse the mice and draw them out for the cat?

In the closet, the dahlia tubers were packed in cardboard boxes in peat moss, according to instructions. This is the first year I have tried to save my dahlia tubers, hence not being prepared to do so. This past growing season, not only did I invest in more tubers than usual, but I grew some from seed. It was the exciting results of my seeds that inspired me to try to save the tubers. The tubers were huge! I expected them to all be about the size of tubers I buy in the spring, but even the plants that were new this year had tuber masses the size of a soccer ball.


My husband suggested we also use the low heat wire that I run through soil for starting seeds in the spring. It is quite long enough to thread through a few trays of seedlings. I randomly distributed it over the top layer of peat moss. To retain more warmth, I topped this with a piece of indoor/outdoor carpet that I had found while cleaning the closet. Then, the roll of bubble wrap went on top of that. With the closet doors closed, I have high hopes that the dahlia tubers will be kept just warm enough in spite of single digit nighttime lows predicted for the winter.

To help monitor this, I will be using my husband’s laser thermometer at different times of the day. This is a very convenient way to check temperatures in multiple locations. It is held like a gun and pointed at the surface or area that is going to be temped. I have compared the temperature inside the closet to the temperature right inside the cat door. There is a difference of  5° F. Inside the closet is at least 15°F higher than the outside temperature. The difference ratio should be consistent enough that I don’t have to get up in the middle of the night to check the temperatures. I have a little more work to do before I can be reasonably confident that the tubers will stay warm enough with outside lows near 0°F.


Another method we may try is getting a temperature monitoring outlet and a small space heater. The outlet would then turn the heater on and off according to the temperature we set it at. We would, of course, use it according to all safety precautions.

When problem-solving this, I came across a few other tactics for retaining or producing heat in a garage. One of the most complicated was putting heating elements in the cement floor, something presumably only worth considering for new construction. A twist to a rather ancient solution is to build outdoor animal housing, such as chicken coops or goat lean-tos attached to an outer garage wall. This would also keep the animals and their water warmer, as well as be an extra deterrent against predators. Some people put wood or pellet stoves in such spaces where they want the option of temporary heating.

The fact is that I had very little idea what I would do when I first realized it needed to be done. It was rewarding to see a bit of brainstorming and research blossom. Maybe next year I will have a more sophisticated set-up, but for now, I am quite pleased with my quick garage insulating make-over!

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