Downward opposed flow flame spread over solid polymers is a benchmark configuration in fire science. It couples solid-phase heating and pyrolysis with gas-phase combustion in a constrained geometry. As a reference material, polymethyl methacrylate (PMMA) is especially useful because it decomposes mainly by depolymerization to methyl methacrylate (MMA), with limited competing decomposition pathways. As a result, it tends to soften rather than melt and flow (Drysdale, 2011), and its pyrolysate composition remains well-defined. This makes PMMA well suited for validating coupled condensed-phase degradation and gas-phase oxidation in flame spread simulations. Recent opposed-flow experiments report surface resolved temperatures, pyrolysis onset relative to the flame front, flame standoff distance, and spread rates for a range of flow velocities and oxygen concentrations. These experiments provide a strong basis for validating coupled solid-gas CFD models under well characterized conditions. In the present work, we present a fully coupled CFD–pyrolysis framework embedded in OpenFOAM and analyze whether it reproduces the key observables of downward PMMA flame spread for multiple operating points. Pyrolysis and gas release are modeled with the Porous Material Analysis Toolbox (PATO) (Lachaud and Mansour, 2014). The model incorporates conjugate heat transfer, the polymer’s pyrolysis, and finite-rate MMA oxidation in the gas-phase (described by the mechanism of Dakshnamurthy et al., 2019). The numerical approach is validated against the experimental dataset of Morrisset et al. (2024a; 2024b; 2025), including surface resolved phosphor thermometry with CH* chemiluminescence, gas- and solid-phase temperature distributions, and spread rate measurements for different flow velocities (0–3 m/s) and oxygen levels (21–40%). Validation focuses on (i) gas- and solid-phase temperature distributions, (ii) the pyrolysis–flame offset (x_p − x_f), (iii) the standoff distance (β), and (iv) spread rates. Together, these metrics enable an assessment of model fidelity and demonstrate the model’s capability to accurately represent flame spread using detailed gas-phase kinetics, without additional calibration factors.