The emergence of the Smart Textiles field opens possibilities for designers to combine traditional surface fabrication techniques with advanced technology in the design process. The purpose of this work is to develop knowledge on interactive knitted textiles as materials for architecture and to do so through practice-based design research. The thesis formulates a research program in order to frame the design explorations, in which scale and material expression are major placeholders. Consequently, Relational Textiles for Space Design is defined as a research program with focus on surface aesthetics and the program is illustrated by design experiments exploring the expressiveness of light, heat and movement as design materials. As a result of the research presented in this thesis, a new methodological framework for interactive textile design is proposed. The framework defines field of reference and frame of reference as basic notions in surface design. These notions form a basic frame used to revise and present the methods behind the design examples Knitted Light, Touching Loops, Designing with Heat, Tactile Glow, Repetition and Textile Forms in Movement. Relating the space of Relational Textiles for Space Design to existing surface methodology in architecture gives rise to new issues that need to be addressed. For which levels of the design process will these textiles be integrated? The last chapter reflects on the role of Relational Textiles for Space Design as possible methods or expressions in the existing space of surface prototyping.