In a new build the fireplace installer came to install the last portion of flue, cap, and "crown" - in my case all of this is metal. They left without saying anything (probably normal since they are used to working with general contractors who may or may not even be on site).
After they left when I looked up the flue chase I can see light coming from between the flue and chimney "crown" which is made of metal. It is hard to tell exactly because it is probably 23' off the ground but it appears there is maybe up to 1/2" of space between the flue and the "crown" in some spots.
I called the installer and asked if this was normal. They said they install clear silicone between the flue and chimney crown. Is it normal to be able to see that much light? It doesn't seem like you'd want to rely on silicone to keep that big of a gap sealed.
Edited to specify "crown" versus "cap". The space between the flue and the crown which covers the chimney chase.