The finished room over the garage or the FROG as it is called in the real estate world seems like a great bonus for everyone. The builder sees it as an easy way to add inexpensive square footage to a house plan. Homebuyers see the FROG as a versatile living space that could be a bedroom or a media room, office or “man cave.” Shortly after moving in, however, many homeowners discover to dirty secret of the FROG; it is just uncomfortable during summer and winter.
This is no surprise considering how they are designed and insulated. When you think about it, the FROG is really like an island thermally speaking. Five out of the six surfaces have unheated/cooled space on the other side. The floor has the garage under it. The knee walls are typically 4 to 6 foot walls that have small attic spaces on the other side; and the ceiling usually has a very small tight attic overtop.
Lets consider the floor first. Usually, the joists under the floor run perpendicular to the soffits. These joists are usually 8 to 10 inches high are 16 inches on center and there is usually an R-19 batt of insulation between them. While it is good that there is at least some insulation between the joists running under the floor, the homeowner is still very likely to notice that the floor is cold in the winter. The reason for this is airflow. The cold air from outside in the winter enters through the soffit vents and then pours into the cavities between the joists. Fiberglass insulation does nothing to stop airflow so the cold air courses like a river under the floor.
Next we can consider the knee walls. If you have an access door into the area behind the knee walls you can take a peek inside and you will notice that there is likely a bat of insulation against the back of the knee wall. Again, some insulation is better than none. But, insulation is not enough. That knee wall is essentially an outside wall. Most of your outside walls have insulation, plus some sort of weather wrap, sheathing and then siding. The inside of your knee wall has only insulation. This allows hot and cold air from that small attic space to penetrate the insulation and greatly degrade its’ performance.
Finally, the space overhead is usually very small and tight. There is often a duct that runs through that space the distance of the room. That space gets very hot. All of the heat from behind the knee walls migrates up there and intensifies. That duct may also be black so you can imagine how much the air-conditioned air in that duct must heat up prior to its’ arrival into the room.
All of these factors make these rooms tremendously inefficient. Fortunately, we can fix these rooms and make them just as comfortable and efficient as any other room in the house. We can do this by sealing the cavities behind the knee walls and bringing them into the building envelop itself (or just air sealing the backs of the knee walls.) We can dense pack the floor spaces with blown insulation via small holes in the garage ceilings to create an air barrier and a strong thermal barrier. Finally, we can air seal, insulate and place a radiant barrier into the space above the room to block radiant heat from entering the long duct run and the rooms ceiling. Then, you have tamed your FROG and can enjoy it all year long!
Michael D. Zande, Ph.D. is VP and co-founder of ProActive Energy Systems, Inc. A Raleigh, NC based company that specializes in residential energy efficiency retrofits for existing homes.
