Putting pictures in your post

Up in the attic, I noticed a bath fan (4 in.) was connected to 3 in. ducting with just duct tape and no reducer. Furthermore, the ducting at the roof end looked quite mangled. My guess is it had been that way for at least 10 years, however with cold but not freezing temps, it doesn't seem to have caused other damage. [[URL="https://i.imgur.com/hGboefx.jpg"]image[/URL]] With that said, I believe the proper thing to do is to replace the existing 3 in. with new 4 in. ducting. A couple questions come to mind: [LIST=1] [*]Besides the UL cert, is this [URL="https://www.homedepot.com/p/Everbilt-4-in-x-8-ft-Semi-Rigid-Aluminum-Duct-A048-20-AHD/205046942"]regular[/URL] duct worse in build quality than the [URL="https://www.homedepot.com/p/Everbilt-4-in-x-8-ft-Heavy-Duty-Semi-Rigid-Aluminum-Duct-MFX48ULXHD12/203626513"]"Heavy Duty"[/URL] duct? The local Lowes has the same two types but doesn't claim one to be heavy duty. [*]What type of connection at the roof will I likely be dealing with? Should I be prepared with some screws, foil tape, clamp, or other? [/LIST]

It's -25 outside today, -50 windchill. I've had this issue in the past, but more than at least a year ago. Getting a wet spot in the bathroom on the ceiling, and in the bedroom directly on the exact opposite side of the bathroom spot, so basically under each end of the same ceiling joist if that makes sense. ( bathroom window facing east, bedroom window facing west) I have a attic hatch that had some minor gaps around it( just sealed it off with plastic) after I saw the leaks. I don't want to open it to go up there to let all that heat in until it warms up outside. The roof has soffit vents and static vents, and a vent in the bathroom which we run all the time during showers and 30 mins after. My only thought is not enough insulation in those spots in the attic? I have no idea.... Why is this happening just now on a record low temperatures? The house is built 1986, 2 story...