The commercial software package FemLab, which is written in the MatLab environment, may be used to solve building physics problems based on partial differential equations. Systems consisting of coupled partial differential equations with up to 32 independent variables, which are one-, two- and three-dimensional, nonlinear and time-dependent, may be simulated. Use of the software is illustrated by modelling: a two-dimensional stationary thermal bridge; two-dimensional dynamic air flow using Navier-Stokes and buoyancy equations; one-dimensional dynamic nonlinear moisture transport in a porous material; and three-dimensional combined heat and moisture transport in a brick. FemLab can use MatLab visualisation tools, toolboxes, and other programs written in the language. 5 refs.