Question: Our son has an attached garage, which is insulated except for the 16-foot-wide vehicle door. His bedroom has a common wall with the garage, and it’s quite cool in the bedroom at night in the winter. How much would the garage temperature rise in the winter if the garage door was insulated?
— Thanks, Don Wiebe
Answer: Insulating a current garage door, or installing a new insulated unit will do little to warm a cold garage. Ensuring it is well-sealed at the jamb and floor may make it possible to prevent cold air intrusion, but unless the garage — or the floor below the bedroom — is heated, there may be little that can be done to warm the bedroom.
Some of the most common questions I receive are about attached garages and problems with moisture and condensation. Fewer inquiries address the other problem that you have identified. This is likely due to improved construction methods for newer homes with bedrooms above the garage. Still, it is not unusual to have complaints from homeowners that their bedroom, often the master suite, is cooler than other areas of the home. The simple answer to this dilemma will be familiar to anyone who has a home or cottage built over a crawl space. Regardless of the method or quality of insulation, the floor will always be cool unless the space underneath is heated. This may be compounded in many "cab-over" homes, due to a common wall at the end of the bedroom that is adjacent to the garage attic area.
It may be possible to increase or improve the insulation and air sealing at the wall area, often by installing a couple of inches of extruded polystyrene (XPF) sheathing over the existing insulation. This may prevent some warm air and heat loss from that area to the cold garage attic in the winter, but still may not be sufficient to warm the room to your son’s satisfaction. As well, installing a pre-insulated garage door with a tight seal at the concrete garage floor slab and jamb weatherstripping may help, slightly, but will likely not be enough. The true solution is either to heat the garage itself, or the floor below the bedroom.
Heating the garage may be as simple as upgrading the vehicle door and installing a wall- or ceiling-mounted electric heater, but there may be unplanned consequences of warming the garage in this manner. Excessive condensation, especially on cold windows or exposed foundation grade beams, are likely. Also, chances of moisture damage and mould growth jumps significantly when warming up a garage in -20C weather. Because of this possibility, local homebuilders have developed a garage ceiling insulation and heating combination that can solve this problem. This poorly named "hot box" method incorporates a lower insulated garage ceiling, below the bedroom floor. That allows for the heating ducts for the bedroom to run through this additional void. These ducts will help warm the floor cavity, while the insulation below prevents excessive heat loss to the garage. Because warm air rises, the bedroom floor surface will no longer be as cool, making the entire bedroom appear warmer.
It may be possible to retrofit your son’s home to create the warmer floor system described, but that depends largely on the current height of the garage ceiling. If it is currently high enough to clear the vehicles by a metre or so, then it may be practical. Many of this style of home do not have that allowance, so lowering the ceiling may render the space unusable for vehicle storage. It still may be possible to improve on the current configuration by replacing the existing fibreglass batts with higher-density foam insulation, but that may not help much if there is no heat available for the cavity. Unfortunately, partial removal of garage ceiling drywall and insulation may be required to analyze the suitability of the floor system to improvements.
The overall decision about upgrading the vehicle door should depend on several factors. Is the current door deteriorated? Is it a light metal door, or a heavier wooden model? Does it operate well with the existing automatic opener or does it put a strain on the opener? The answers to these questions should determine whether a new, well-insulated door is desirable. I would recommend against attempting to insulate the current door, unless it is a very light, single-walled metal version. In that case, lightweight XPF may be cut and glued to the inside, providing additional R-value and lessening the chance of condensation on the cool metal surface. Wooden doors, often panelled, may be much more difficult to adhere insulation to, and may become too heavy for proper operation. If that is the type in your son’s home, upgrading may be the only suggestion for improvement.
While it may seem like installation of a better-insulated garage door makes sense to help warm a cool bedroom above an attached garage, the reality is that may not help much at all. If the current door is older and deteriorated, then upgrading is warranted. Otherwise, major improvements to the insulation and heating of the floor system below the bedroom will be required to eliminate the cold room.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.