  Vacancies play a crucial role in solid-state physics, but their impact on
materials with strong electron-electron correlations has been underexplored. A
recent study on the Ir-Sb binary system, Ir$_{16}$Sb$_{18}$ revealed a novel
extended buckled-honeycomb vacancy (BHV) order. Superconductivity is induced by
suppressing the BHV ordering through high-pressure growth with excess Ir atoms
or isovalent Rh substitution, although the nature of superconducting pairing
has remained unexplored. Here, we conduct muon spin rotation experiments
probing the temperature-dependence of the effective magnetic penetration depth
$\lambda_{eff}\left(T\right)$ in Ir$_{1-{\delta}}$Sb (synthesized at 5.5 GPa
with $T_{\rm c}$ = 4.2 K) and ambient pressure synthesized optimally Rh-doped
Ir$_{1-x}$Rh$_{x}$Sb ($x$=0.3, $T_{\rm c}$ = 2.7 K). The exponential
temperature dependence of the superfluid density $n_{\rm s}$/m$^{*}$ at low
temperatures indicates a fully gapped superconducting state in both samples.
Notably, the ratio of $T_{\rm c}$ to the superfluid density is comparable to
previously measured unconventional superconductors. A significant increase in
$n_{\rm s}$/m$^{*}$ in the high-pressure synthesized sample correlates with
$T_{\rm c}$, a hallmark feature of unconventional superconductivity. We further
demonstrate a similar effect induced by chemical pressure (Rh substitution) and
hydrostatic pressure in Ir$_{1-x}$Rh$_{x}$Sb, highlighting that the dome-shaped
phase diagram is a fundamental feature of the material. These findings
underscore the unconventional nature of the observed superconductivity, and
classifies IrSb as the first unconventional superconducting parent phase with
ordered vacancies.
