I’m building a demo that will consist of several rooms from a mansion and it is modular in design. I’ve gone through the Lighting Troubleshooting Guide and tried several of the fixes including leaked lighting, two sided materials, my UV light map layout and also tried extruding a couple of my meshes into boxes(currently using plane meshes) thinking it would block out the light. With the attenuation radius on my light overlapping into Room A, how do I prevent it from affecting Room B?
Since you mention light maps I presume you are baking the light? You said you have already checked your meshes for leaks so its probably lightmass.
In lightmass you generally need to turn the settings up to get a high quality bake that does not penetrate. In your world settings>Lightmass. Try turning your level scale down slightly, your indirect lighting quality up, and your smoothness down. The level scale has the most impact, as it will directly increase your samples. It will have a MAJOR effect on your bake times as well. Try just increasing quality to 3, smoothness to .8, see how it is. If its still bad try taking the scale to .75. In production bakes I have seen scale set to 0.1. Render time jumps to easily 6+ hours for a tiny level.
I was using baked lighting, or setting up to do so but I ended up with light spots(similar to a disco ball) everywhere. Tried numerous fixes for it and decided for the demo, to go with stationary for now, and if I have time to find a fix for it, switch to static lighting and tweak the lightmass settings as you suggested.