Bonus rooms are a popular feature for homebuyers. The additional space, usually over a garage, is nice to have for an office, playroom or extra bedroom. Bonus rooms that are too hot in the summer and too cold in the winter are also one of the most common complaints by homeowners.

Unlike other rooms in the house, a bonus room over the garage has unconditioned space all around it, including under the floor. Because of this, it starts out having more heating and cooling demand for its size. In addition, these rooms frequently are not properly insulated, particularly between the floor and the garage, and often have a number of air-infiltration paths, usually from plumbing and wiring penetrations that aren't properly sealed.

Builders often put the floor insulation on the garage side of the sheetrock, when it should always be next to the part of the house that's warm in the winter. Because the insulation is lying on top of the garage-ceiling sheetrock, a gap is formed below the bonus-room floor where air can move. Moving air doesn't have any insulation value, and in summer, that space forms a path for warm air to rise to the bottom of the floor. While the insulation should be attached to the floor, in an existing house you may want to have a contractor blow in additional insulation between the garage and the bonus room. This procedure can be costly, so it's best to determine if the level of discomfort outweighs the cost before you make any decisions.

Bonus rooms over the garage and in attics often have ceilings that follow the pitch of the roof and knee walls, the short walls below the lower ceiling. Knee walls not only need insulation, but also sheathing on the other side. This increases the performance of the insulation in the summer when attic temperatures soar. The sheathing should be sealed to keep air from moving through the insulation. Otherwise, the space acts like a chimney, with the rising — and moving — warm air negating the effect of the insulation. Bonus rooms may have doors to unconditioned portions of the attic used for storage. These doors should be insulated and sealed with weatherstripping.

Since bonus rooms are so difficult to heat and cool, also be sure the room has as many other energy-efficiency features as possible, including sufficient ceiling insulation and well sealed double-glazed windows.

Heating and air-conditioning contractors frequently suggest adding more heating and cooling to the bonus room or zoning the heating and cooling system. That may be necessary, but the first step is to solve the insulation and airflow problems. It's almost impossible for an air-conditioning system to cool this space if heat is pouring into the bonus room because of insufficient insulation or penetrations through the floor and walls.

Homeowners can make many of these improvements on their own, including sealing penetrations around plumbing and wiring, sheathing the knee walls, and sealing and insulating openings to unconditioned space. Jobs like blowing in additional insulation are best left to professionals.

It is possible for your bonus room to be a comfortable space you can use year round. A Right Choice High Tech Audit can pinpoint the reasons why your bonus room is difficult to heat or cool and suggest solutions.