Will an unheated New Brunswick garage stay above freezing?

An unheated garage in New Brunswick will not reliably stay above freezing — in fact, during a typical NB winter, an unheated garage will spend weeks at a time well below 0°C, often tracking within a few degrees of the outdoor temperature.

This is one of the most common misconceptions NB homeowners have when planning a garage. The idea that a closed building will somehow hold warmth is understandable, but in practice, an uninsulated, unheated structure with a large metal overhead door, concrete slab floor, and minimal thermal mass loses heat almost as fast as the outdoor air cools. When it's -20°C in Moncton or Fredericton in January, your unheated garage might be -17°C or -18°C inside — cold enough to freeze pipes, damage stored liquids, and make the space completely unusable for any hands-on work.

What actually keeps an unheated garage slightly warmer than outdoors is the wind protection it provides and a modest amount of solar gain through any windows on south-facing walls. On a calm, sunny winter day, an unheated garage might be 3-5°C warmer than the outside air. But on a cloudy, windy night at -25°C, that difference essentially disappears. You cannot count on an unheated NB garage staying above freezing from November through March.

What This Means Practically

If you're storing a vehicle, the cold itself won't damage a modern car — engines, transmissions, and fluids are designed for NB winters. What the freeze-thaw cycle does damage is anything with water in it: a pressure washer left with water in the pump, a garden hose, paint cans, caulking tubes, certain adhesives, and any plumbing you've run to a utility sink or hose bib. If your garage has a floor drain with a water trap, that trap will freeze and crack. Plan your storage accordingly — anything water-based either needs to come inside for winter or be fully drained before freeze-up.

Battery-powered tools are another consideration. Lithium-ion batteries stored in a consistently sub-zero environment degrade faster and lose charge capacity over time. A small heated cabinet or bringing your tool batteries inside during the coldest months extends their lifespan significantly.

The Insulation Question

Here's where many NB homeowners get caught in a middle ground that causes problems: a garage that is insulated but not heated is actually more complicated than one that is either fully heated or completely uninsulated. An insulated but unheated garage will still drop below freezing — it just does so more slowly. The insulation slows heat loss but provides no heat source, so the interior temperature eventually equalizes with the exterior over a long cold snap. What insulation does do in this scenario is trap moisture, because the warm-side vapour barrier and insulation slow drying. If you insulate without heating, you need to be especially careful about vapour barrier installation and ventilation.

The practical threshold in NB is this: if you want the garage above freezing reliably, you need both insulation and heat. A well-insulated two-car garage (R-20 walls, R-40 ceiling) with a properly sized propane or natural gas unit heater can be maintained at 5-10°C for a surprisingly modest heating cost — roughly $600-$1,200 per winter depending on fuel prices and how warm you keep it. That modest investment protects everything stored inside, prevents pipe freeze-ups, and makes the space usable for weekend projects even in February.

If heating isn't in your budget or plans, build the garage uninsulated, accept that it will be cold all winter, and store only freeze-tolerant items. Don't run plumbing to it without a reliable heat source, and drain everything water-based before November.

If you're weighing whether to add insulation and heating to a new garage build, that's a great conversation to have with a contractor before construction starts — it's far cheaper to rough in a gas line and insulate during the build than to retrofit later. New Brunswick Garages can match you with local contractors who build heated garages regularly and can give you accurate estimates for your specific situation.