Q. My utility bills are too high and my house is uncomfortable year-round. Two masonry walls are totally uninsulated and I want to add more insulation to the other walls too. What is the best do-it-yourself method? — A.G.

A. Adding wall insulation, especially on solid masonry or concrete block walls, can lower your utility bills significantly. By keeping the walls warmer in the winter and cooler in the summer, you feel more comfortable without having to wastefully raise or lower your thermostat.

The easiest and most efficient method is to add insulation to the exterior wall surface of your home. With the insulation on the outside of your walls, the entire structure under the insulation stays near room temperature year-round. This moderates temperature changes throughout the day and night and lowers your heating and cooling costs.

Attaching several inches of rigid foam insulation board (polystyrene or polyurethane) on the outside of your walls is the easiest and most common method. Several inches of rigid foam insulation are typically added for a substantial insulation level improvement. This is also a very effective insulation method for new construction.

There are several companies that manufacture special new and retrofit exterior insulation systems. Some are only applied by licensed contractors and others are for the do-it-yourselfer. These manufacturers can sell you all of the materials needed or you can purchase some common materials locally.

Depending on your existing exterior wall finish, you can attach the rigid foam board insulation to your existing walls with special adhesives, mechanical fasteners, or both. The rigid foam board is easy to cut so you can fit it neatly around the openings for doors and windows.

Next you apply a reinforcing mesh and thin layer of cement-like material over the insulation. This adds strength to the entire insulation system and provides a smooth surface for the finish coating.

The most commonly used type of finish coating is a special flexible stucco-like coating. It looks just like stucco, but it is made of flexible acrylic polymer. It is impregnated with coarse sand to simulate the true feel of real stucco, and is more durable. It is available in many colors.

You can apply the coating with a trowel, a roller, or a sprayer depending upon the surface finish you desire. One-sixteenth of an inch is the recommended thickness. Trowel it on around the corners and window trim right up to the brick or exterior surface for a professional look.

You can write to me for Utility Bills Update 434 listing the manufacturers of exterior insulation systems, information and specifications on the do-it-yourself system and materials, and a small sample piece of cured do-it-yourself flexible stucco finish coating. Please include $1.50 and a self-addressed business-size envelope. Send to James Dulley, 6906 Royalgreen Drive, Cincinnati, Ohio 45244.

Q. There is quite a large gap in some spots where my garage door meets the floor. It lets a lot of air blow in when I heat the attached garage and work on my Jaguar XKE. How can I seal the gap? — V.T.

A. Even if you do not heat your garage, the air leaking into the garage can make it colder in the winter and hotter in the summer. This can cause adjacent rooms to be hotter or colder.

You can buy special rubber sweep weatherstripping for garage door bottoms. I have also used 3/4-inch foam pipe insulation under the door. Nail it to the bottom of the door, about 1/2 inches back, with the slit facing down.

James Dulley studied energy management at the doctoral level at Harvard.