Theoretical and practical considerations are, very often, poles apart. It is important therefore that the engineer should be alert, at all times, to offer evidence to show that his designs are behaving in a manner similar to that assumed when the calculations and detail drawings were being prepared. This article describes the structure of a paper store constructed at Watford for Messrs. Sun Printers, Ltd. The main item of interest in the design is that of the northlight portal frames. The various moments in these were calculated by strain energy methods. The movement of one of the frame legs was computed and deflection tests were carried out by a simple method, during construction.