Buildings with intelligent façades made of membrane elements respond to the influences of light and wind by automatically adopting their envelope. The automated covering reanalyzed by stretching the membrane, contributes to an eco-friendly and optimal climate inside the building. To minimize the wearing of the membrane at any state, the strain of the membrane is monitored and the clamping force is controlled. ARAMIS is a standard method for measuring material expansion under laboratory conditions. Fiber-Bragg-Grating-sensors (FBG) can be installed on a building façade made of membranes and allow the measurement of strain within the membrane. The installation of sensors causes stiffening, which will be registered as a subdued expansion by the FBG sensors. This work investigates the use of FBG sensors and ARAMIS for strain measurements of membrane façades. The subdued expansion of the FBG sensor is modeled by a linear transfer function and a non-linear artificial neural network (ANN).