This article reviews a recent body of Work that documents the heat flow through walls With relatively complicated internal structure. The first part presents the fundamentals of natural convection heat transfer in two-dimensional enclosures filled with air. Numerical simulations for Rayleigh numbers in the range 6000-30000 and aspect ratio A = 40 show that the air circulation is periodic (pulsating) and the core space is dominated by almost equidistant rolls. The heat transfer effected by such flows is documented, and the application to walls with tall cavities (hollow bricks) is discussed. The paper continues with a study of heat transfer through a ventilated wall heated by solar radiation from the side. The heated side is ventilated by an air channel opened at both ends. It is shown that the design of the air channel has a significant effect on the share of the radiative heat input intercepted by the air flow. The concluding part of the paper is a first-time review of new work on natural convection heat transfer across elongated vertical cavities with deformed side walls (e.g. air gaps in double-pane windows). It is shown that when the side walls are bent inward so that the cavity is narrower at mid-height than at its top and bottom ends, the total heat transfer rate through the system is increased significantly. The deformation of the walls also affects the intensity and structure of the buoyancy-driven flow in the air space. Overall, this article reviews some of the newest work on heat losses through complicated wall structures and projects it on the background provided by the existing literature. Copyright (C) 2002 John Wiley Sons. Ltd.