“A man’s home is his castle” is an old familiar phrase, but if truth be told, the castles of old were cold and draughty. Today’s homes are now havens of comfort with efficient central heating systems and well insulated building envelopes. We count on the walls and roofs of our houses to keep the heat in during the winter months and the heat out during the sweltering days of summer. Today’s home buyers demand energy efficient houses with high insulation values. “Lowering energy use” has become the goal as the cost and environmental implications of energy use are considered. Insulation levels are now being required by many code authorities. Stricter thermal requirements mean that designers must understand the impact of the materials and assemblies used on thermal performance. Because of its long history of use, wood-frame construction has well established insulating properties and record of performance. The effect of other construction systems on insulation properties is not widely known or understood. This publication will examine current knowledge of the thermal performance of wood and other framing techniques. This information will assist designers and builders to select construction techniques that provide the best thermal performance.