Given a family (µ λ , λ ≥ 0) of integrable mean-zero probability measures such that, for every λ ≥ 0, µ λ is the image of µ1 under the homothety y −→ √ λy, we provide a necessary and sufficient condition on µ1 under which the Root embedding algorithm yields a self-similar martingale with one-dimensional marginals (µ λ , λ ≥ 0). Precisely, if τ λ and R λ denote the Root solution to the Skorokhod embedding problem (SEP) and the Root regular barrier for µ λ respectively, then this condition is equivalent to the property that (R λ , λ ≥ 0) is non-increasing in the sense of inclusion, which in turn is equivalent to the assertion that (τ λ , λ ≥ 0) is non-decreasing a.s. We show that there are many examples for which this result applies and we provide some numerical simulations to illustrate the monotonicity property of regular barriers (R λ , λ ≥ 0) in this case.