A method for measuring and/or monitoring the surface moisture of building facades in a surface region, wherein the method comprises the following steps: a) arrangement of a light source fastened to a supporting device at a distance from the surface, such that the beam path of an incident light beam, which is produced by the light source, strikes the surface region at an angle of incidence a, b) reflection of the incident light beam by water adhering to the surface region, at an angle of reflection β, such that the beam path of a reflected light beam is formed with a light intensity, in particular a degree of reflection, c) detection of the reflected light beam by a light sensor fastened to the supporting device, which sensor is arranged in the beam path of the reflected light beam, d) evaluation of the output signal of the light sensor, wherein a surface moisture is assigned to the light intensity, in particular the degree of reflection, of the reflected light beam, and wherein a change in the surface moisture is tracked by way of a change in the light intensity, in particular in the degree of reflection, of the reflected light beam, wherein the angle of reflection β corresponds to the angle of incidence α or the deviation of the angle of reflection β from the angle of incidence α is not more than 15°, the light source is a pulse light source having a pulse frequency of 10 kHz to 70 kHz and the light sensor and a data processing device connected to the light sensor separate the pulse signal from continual interference signals, the light source emits radiation in the wave range from 820 nm to 1.5 μm, and wherein the light sensor comprises at least one optical filter in order to filter out daylight and/or visible light substantially completely or predominantly, and/or the light sensor is adjusted to the wavelength range of the light source, characterized in that the angle of reflection β and the angle of incidence α are greater than 48.6°, that the light sensor comprises a photodiode array and/or the light sensor is formed by multiple photodiodes on a chip together with an integration and readout circuit, and that the distance on and/or in the supporting device between the light source (2, 102, 202) and light sensor (16, 116, 216) is 20 to 60 cm. a) arrangement of a light source fastened to a supporting device at a distance from the surface, such that the beam path of an incident light beam, which is produced by the light source, strikes the surface region at an angle of incidence a, b) reflection of the incident light beam by water adhering to the surface region, at an angle of reflection β, such that the beam path of a reflected light beam is formed with a light intensity, in particular a degree of reflection, c) detection of the reflected light beam by a light sensor fastened to the supporting device, which sensor is arranged in the beam path of the reflected light beam, d) evaluation of the output signal of the light sensor, wherein a surface moisture is assigned to the light intensity, in particular the degree of reflection, of the reflected light beam, and wherein a change in the surface moisture is tracked by way of a change in the light intensity, in particular in the degree of reflection, of the reflected light beam, the angle of reflection β corresponds to the angle of incidence α or the deviation of the angle of reflection β from the angle of incidence α is not more than 15°, the light source is a pulse light source having a pulse frequency of 10 kHz to 70 kHz and the light sensor and a data processing device connected to the light sensor separate the pulse signal from continual interference signals, the light source emits radiation in the wave range from 820 nm to 1.5 μm, and wherein the light sensor comprises at least one optical filter in order to filter out daylight and/or visible light substantially completely or predominantly, and/or the light sensor is adjusted to the wavelength range of the light source,