As the title said, even though our version of 5.0 is a mix of different Korean patches it doesn't include the second UCC House patch which allows quite a few more houses to have UCC walls/floors/ceilings.

1st patch includes:

-16x16 houses (not upgraded)
-24x24 houses (not upgraded)

2nd patch includes

-16x16 houses upgraded
-24x24 houses upgraded
-28x28 houses (normal and upgraded)

I hope this helps and lets you know why your house has the ucc option grayed out!