If an exposed timber beam is preferred then a calculation is generally required to demonstrate how much inherent fire resistance it has - dependent on it's size and species of timber.
Pe baech yn ffafrio trawst pren agored, byddai angen cyfrifiad fel rheol i ddangos beth yw gallu cynhenid y trawst i wrthsefyll tân – bydd hynny'n dibynnu ar faint y trawst a'r math o bren.