Present and future research will be oriented towards both industrial construction techniques and sustainability, and in this sense combination of mass production and sustainable houses is of a special relevance. Modular construction is a very successful building method in some countries such as Japan and U.S.A., and could be easily applied in solar houses production. In this way it is worth to refer to Solar Decathlon competition, promoted by the U.S.A. Department of Energy, as one major laboratory of solar house prototypes, most of them being modular homes. As a progress report of modular construction applied to solar houses research, whose first paper was released at “II Jornada de Investigación en la Edificación EUATM”, Madrid 2008, in this study relationship between the modular system and space layout of solar houses from Solar Decathlon 2005 and 2007 are explored. This research will allow for a new open understanding of spatial design of each house regarding the influence of the modular construction type employed on them. It actually is an essential Knowledge to discover which the spatial and formal possibilities provided by these systems are, what in fact will be invaluable for future designers and builders. In a further stage a full set of construction design criteria will be obtained for their application to solar houses construction.