I'm installing a stone veneer on top of a brick/cinderblock chimney with
2x4" studs and 7/16" OSB on top of that. The website for the company says to use 15 lb asphalt-sturated rag felt or ASTM226 over the OSB. This is for an inside fireplace. Is the weatherbarrier really necessary? I couldn't find a distinction about whether they were referring to an indoor/outdoor installation.TIA
Matt