Diffusivity is generally measured on small sample under laboratory conditions where each side of the specimen is accessible, but one-side measurement may be necessary in such applications requiring in situ inspection. Experimental results are reported applying a thermoelectric unit in contact with the sample, acting alternatively as heat source and sink and generating thermal waves on the specimen. The read out of temperature is done on the same side, laterally to the source. This allows estimating the diffusivity of the material along the stimulated surface from the peaks displacement velocity or waves phase shifting measurement. Simple formulas coming from an adiabatic model furnish diffusivity values that overestimate the real one with the increase of the harmonic stimulus period. A procedure to extract the real value of diffusivity is proposed.