Why Is There Pvc Pipe In My Attic

It looks like the part that extends up on the left is over the master bedroom the horizontal potion passes over the bathroom and the right hand section that extends up is over the kitchen.
Why is there pvc pipe in my attic. Has anyone come across this before. I always recommend to my clients to consider insulating these lines as an energy conserving addition to the system. Pvc coupling or insert a 3 in to 4 in. Seems that it is an inherent to the nature of pvc itself.
One i m pretty sure is for condensation drainage for when running the air conditioning system. The second pvc pipe right next to the first leaves the unit and exits the house wall high up near the eave. Even though you may think by looking at the photo that it is vertical. It appears to be a plumbing vent intended to exit the roof but is capped.
The pipe is parallel to the ground. The best way to be sure your pipe vents are clear and pipe boots are functional is to have them inspected regularly by either an experienced roofer or by looking. Our plumbing consultants prefer the banded fitting because gluing the large pvc fitting in a tight attic space can be difficult and the solvent fumes in pvc cement can get dangerously intense. Anyways i ve put some epoxy leak fixer around the joint and i imagine that will fix the problem.
Wasn t sure where to post this thread so it seemed what i was looking at was a capped pvc pipe in the attic on a newer constructed house 7 yo so plumbing seemed appropriate. On a slighly different note i m looking at whole house vac system installation as well which also uses schedule 40 pvc or thinner through the attic. Plastic pipe in the attic any guesses as to why there s plastic pvc in the attic. On the roof these are covered with lead flashing to prevent water from getting inside the house.
I have this pvc pipe in my attic that is leaking at this joint in the photo. Why would they run the pipe cap it. I have been doing a lot of. Looks like other variants cpvc have higher temps but i don t believe there are any nec listed products.
In my house attic i have several 4 inch white pvc vent stacks which are simply white pvc drain pipe extending from the wall headers through the attic and the roof. Then either glue in a proper 3 in to 4 in. I have two pvc pipes that come out of my attic furnace unit. The gray stuff is blown insulation.