The Wire-Arc Additive Manufacturing (WAAM) process is an increasingly attractive method for producing porosity-free metal components. However, the residual stresses and distortions resulting from the WAAM process are major concerns as they not only influence the part tolerance but can also cause premature failure in the final component during service. The current paper presents a method for using neutron diffraction to measure residual stresses in Fe3Al intermetallic wall components that have been in-situ additively fabricated using the WAAM process with different post-production treatments. By using averaging methods during the experimental setup and data processing, more reliable residual stress results are obtained from the acquired neutron diffraction data. In addition, the present study indicates that the normal residual stresses are significant compared to normal butt/fillet welding samples, which is caused by the large temperature gradient in this direction during the additive layer depositions.