<p>Sills constructed offshore of marshes can increase the wave attenuation capacity of living shorelines by increasing bottom friction, inducing premature wave breaking, and causing wave reflection. This study used new field measurements from three living shorelines located along the coast of North Carolina, USA, with varying oyster shell and granite sill structures to (1) quantify wave attenuation across the sill and (2) analyze the skill of a one-dimensional model of wave energy dissipation based on the conservation of energy flux in representing this attenuation. Special attention is paid to parameterizations of wave breaking and friction to improve the representation of sills. Wave transmission decreased strongly as the ratio of wave height to water depth above the sill increased. The transmission coefficient (<i>K</i>_<i>t</i>), defined as the ratio of transmitted to incident wave height, ranged from 0.4 to 1.4, with values greater than unity resulting from shoaling. The model captured wave attenuation across sills with a mean average error of less than 10% of incident wave height, though transmitted wave heights are generally slightly underpredicted for larger waves (root mean square wave height <i>H</i>_rms &gt; ~ 0.08&#xa0;m) and overpredicted for smaller waves (<i>H</i>_rms &lt; ~ 0.08&#xa0;m). Possible improvements to the model and factors controlling this dependency are discussed. The model predicts wave attenuation across the sills well for the range of wave conditions and water depths in this study, and it is simple to parameterize and implement, and therefore has potential to aid in the evaluation and design of living shorelines.</p>