In 1977 the Canada Mortgage and Housing Corporation (CMHC), with the technical assistance of the Division of Building Research, produced the publication Road and Rail Noise: Effects on Housing . That paper presented procedures for predicting the noise from road and railway traffic, and specified acoustical requirements for residential buildings in their vicinity. The procedures were simplified to the point where they can be handled by persons with limited mathematical training and no knowledge of acoustics. The objective of this present paper is to describe the underlying acoustical principles and explain how they relate to the procedures given in the CMHC document. The paper is divided into nine sections, roughly paralleling the steps in the CMHC document.