If you were to ask a homeowner what the most uncomfortable room in the house was, most of them would say “the bonus room” (of course assuming they have one). The one room in the house that is always colder or hotter than the rest of the house. Usually, these rooms are located over the garage. It is truly amazing how one room can consistently be a problem, regardless of the builder. So what is it about a bonus room that makes it far from a bonus?
First let’s look at a bonus room’s overall design. As I said before, generally these rooms are located over a garage. Four or five sides of the area are usually in contact with unconditioned space, the top, the bottom and two or three walls (in the worst case scenario all four walls). In most cases, the bonus room area is a single large room, but in some cases the bonus room area can be part bathroom and walk-in closet. These areas are often part of a gabled roof area, which restricts the width of the upstairs room and often leads to creative interior wall design to maximize the space.
Now let’s look at what contributes to the lack of comfort in a bonus room. One of the biggest problems is related to insulation. Both quantity and the quality in which it was installed are major issues, because there is usually not enough insulation and more than likely it was poorly installed. The insulation in the floor (if there is any) is installed before the sheet rock is applied to the garage ceiling. Over time, or even upon installation, the batts are no longer in contact with the subfloor above. Once this gap occurs, air from the never air sealed band joists pours into the area and the insulation is now basically worthless.
Knee walls are also a major contributor to bonus room miseries. Those vertical walls between the conditioned interior space and attic space are often neglected. If you’re lucky (or unlucky depending on how you look at it), you have access doors or hatches that allow you to get to these areas. Very little attention is given to air sealing these areas so they now become giant leaky radiators (both hot and cold). This then brings in lack of air sealing. It is very difficult to keep the temperature of an area consistent when half the air in the room is leaking in and out through outlet and switch plates, poorly installed windows and hatch accesses, and wall and top plate seams.
Finally, we look at the duct system that’s supposed to bring the conditioned air to the area. Just because of the nature of the location of the bonus room, this area is often serviced by one of the longest runs in the duct system. If the ducts are not properly sealed, the air never has a chance to be supplied to or returned from the room. I am constantly amazed how many HVAC contractors recommend increasing the size of the units or number of ducts to the area without even considering the condition of the existing ducts. Even better, the new craze has become zoning. While zoning can be beneficial in some cases, in no case does it improve duct leakage.
How homeowners deal with the issues of the bonus rooms ranges from ingenious to comical and even to pathetic. I recently audited a home with a worst case scenario bonus room. Not only is the very large bonus room over a three car garage, but it also includes a dormer (which is a true vaulted ceiling). There is a small kitchenette in the room which adds plumbing penetrations to the list. The walls below the roof penetration of the dormer are not insulated and there are no hatches or doors to access the areas. The homeowner had a new HVAC zoning system installed and also added weather stripping to the room’s door so he can cut off the heat to the area and seal the room shut. They only use the room when they have company. The problem with this (besides the obvious reduction in living space) is that this area now becomes unconditioned space. This makes the uninsulated interior walls between the bonus room and the rooms on the other side the equivalent of a kneewall. Brilliant! Space heaters, window air conditioners, fans, and yes even interior weather stripping are nothing more than masks for the problems, not cures.
Like every home, every bonus room is unique. But like many homes, especially those here in Atlanta, there are common issues that can be easily identified and addressed by a qualified energy auditor and home performance contractor. Using building science (and a little common sense), we can turn these bonus rooms into an actual bonus. Remember, don’t throw money at your problems, throw knowledge, it’s a lot cheaper.