H implantation results in the appearance of tensile out-of-plane strain in the implanted region which evolves during further annealing. VnHm complexes and/or larger platelets, both co-precipitates of vacancies and H atoms, are believed to be responsible for strain generation. However, during H+ implantation, Frenkel pairs i.e., both vacancies and interstitials are generated. Silicon self-interstitials have been rarely detected and thus their possible role in strain generation has been ignored so far. In this work, we demonstrate that Si interstitials are actually present in large measurable quantities in such implanted layers. For this, we have studied by Secondary Ions Mass Spectrometry the diffusion of boron delta layers during annealing at 350 °C, 550 °C and 850 °C after H implantation at 12 keV with a fluence of 1 × 1016 H+/cm2. The Si self-interstitial supersaturations were extracted by comparison with simulations. Frank dislocation loops, i.e., precipitates of Si atoms, were observed by Transmission Electron Microscopy growing by Ostwald ripening during 850 °C annealing. The supersaturation of Si self-interstitials in dynamical equilibrium with these loops was extracted showing consistency with the values found from the diffusion experiments. These results and more generally the role of interstitials in the strain build up are discussed.