He everyones,
I created a scene on UE4, and it become pretty long to precompute (build) the scene everytine i add some new contents, walls or lights.
I want to know if its possible to build only a little place in the entire scene or a volume alone ? It can permit me to check the incrustation of a new object or a new lights without backing all the scene.
Thanks you 
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That feature is not available in unreal engine 4, even though it should be.
I solved this in our game dividing the baked scene in multiple sub-levels, to bake every time a smaller one instead of the entire one, would it be an option for your level?
Re,
What do you mean Ginwakeup ? Created a layered level (as a multiple lvl), or give to the lightmassimportantvolume a very small size ?
The thing is that, i face some very strange shadow artifacts in my scene, but only with 2/3 meshes (but large, around 10x10m). The backing in medium quality is not enought, so i put it in production quality. But the building need 3h00 to be done…
I can not permit myself too loose all that time everytime i modify my scene or my FBXexport/import to find the probleme :s
For info : My scene is a simple hangar, 10x10m squared size, made in 3DSMAX. But i thought this is too small cause UE4 indicated me that some meshes are to small to be well apprecieted. So i did enlarge (in UE4) my all meshes to something like 55x55m. I use for now only a HDRI Skylight, cubemap rez is 256. My baselightmass.ini is little modified but worked well with an other scene “almost” the same size.
I mean that I have many levels instead of a single one, you know… the sub-levels of the map you are opening every time you open the scene.
Could you share a screenshot of your scene? However, 10x10m meshes it’s big for lightmass: smaller meshes will bring you less artifacts.
For the screen i give it to you tomorow (where i live it is 3 in the morning and i will go to sleep :D) when the scene will be backed for now it look totally black and i can not shot anything.
I didn’t know for the 10x10m scene. I see on youtube lot of exteriors architectures that use GI (and i think its lightmass) with “large” scenes.
Even here some users use the lightmass for large scene :
Maybe the ratio scale is 0.5 (or less). But i doubt it.
After, if i understand, they should change the “static lighting level scale” to 0.1 or 0.2 i think.
If you have a large scene reduce static lighting level scale to 0.1 or 0.2, yes. It will boost up the quality but increase build times.
I will change some data to my lightmass.ini, make it higher, but then buil in medium quality. Also put the level scale to 0.05, and reduce my scene to the normal size and maybe win time (but not sure that the ratio size really have an impact depending how the setting is optimized, sadly iam not a pro :p).
And i will see what it’s give.
Anyway, its sad that theire is no simple option to simply render a selected volume/meshes, in case of building everyhting or passing by different sub-levels.
Maybe some plugin exist about that, but i doubt it.
Anyway thanks for you for help