Emon told me about this little trick after his little conversation with Y. It's always worth trying.
"There was a spider-web (near doors), that casts heavy shadow on doors."
That just reminded me one of the tricks you can do is place a nodraw brush in the doorway then make a solid black texture and tell it to cast alphashadows (surfaceparm alphashadow)...that along with a specific blendFunc (forgot which) should make it transparent but block any light trying to go through the doorway. The two downsides are 1: slightly longer compile time and 2: a small performance hit because the doorway is now a transparent shader instead of 'nothing'...both are usually very small though.
GothiX that 'trick' works when the light is quite literally a leak, nothing more, if light is being cast through the doorway and travels a fair distance then lowering the lightmapscale will just crisp up the shadows.
But it's very unlikely that such a thing happens anyhow, unless one compile with SOWTF2MAP.
Put an area light in front of a door way and watch it go through far :p
Place a spotlight pointed at a doorway.
Place a sun entity pointing towards a doorway.
Use a high value on your skylight.
Have one room much brighter than the one next to it on a bounce compile.
And so on...