Begin in the attic space. Use a string & plumb bob to extend a vertical line from the center of the pipe to the underside of the plywood roof decking and mark the spot. Drill a hole through the roof decking from the underside up through the roof then push a wood dowel, piece of wire or other object through that hole that you will be able to see when on the roof. That will mark the center of hole through the roof. Now go on the roof and locate the center index marker you pushed up. For a 2" pipe I would layout a 3" hole centered on that mark, then cut the hole out with a jig saw. Drop your PVC pipe down through the hole and connect it to the cat iron pipe. If the cast iron pipe has a hub you can get a "Fernco" rubber donut gasket to seal the PVC to the hub. If the cast iron pipe is cut off so that it has a spigot end (raw pipe diameter) you can use a "Fernco" PVC x CI rubber coupling to connect the pipes. Next you will install a "Roof Flashing", which is a flat aluminum plate about 1/8" thick and about 2' x 2' square. The flashing has a hole through the center to fit over the pipe and it has a flexible rubber gasket that seals it weather tight against the pipe wall. The flashing is slid down the pipe and placed tight against the roof. The shingles on the upper side of the pipe should be carefully folded up to allow slipping the upper section of the flashing under the shingles. In this manner any rain water coming down the shingle will go on the top of the flashing plate and continue running down over the flashing and onto the roofing below. The bottom corners of the flashing should be nailed in place to prevent the flashing from moving. Now looking at the pipe from the side you will note the roof angle. The vent must extend 6" above the roof measured from the high side of the pipe on the roof angle. If you live in a region subject to snow the vent must extend 6" higher than your average snowfall. (Check your local AHJ because most communities have set a specific length to allow for snow in your community)

Since you are new to our country, my thought is to ask you about the type of ownership you have. If you truly own the town home from your curb to the back of the lot, the advice you have gotten above works fine. However, if the unit is a condominium or co-operative, things are handled differently. In that case, you probably do not fix a roof problem yourself, you would report it to the condo board or manager, or someone like that because in a condo, you only own what is inside your walls, not the structure itself. A cooperative is likely more complicated than a condo.

Ah man I am sorry for all of your stories. How sad!! In high school and in my early college years I had a horse that I used for rodeo for a few years. I loved that horse something fierce. She was a living doll. She was the most patient kind creature. I used to board her at my work, when I was in high school, and every day I would take my sack lunch out and she would come over and keep me company while I ate. She would also try to steal my chips. Anyways,as I got older and more experienced in rodeo (though still not very good) it became obvious to others around me that I needed a horse that could perform better. My parents told me they thought I should sell her and get a horse that was more of an athlete. I said I will not get rid of her she is to stay in this family until her life is over. I refused to get a different horse all for rodeo which I was never all that crazy about anyway. I quit rodeo and kept my horse. A few years later my brother and his wife found out they were expecting. They had some land and horses and I had been spending more time with friends, work, and school than with my horse. I felt like she would be a great horse for my nephew. I GAVE her to him for his soon to be born son and he was happy to have her. I gave him all of my tack and made him promise to keep her until she died or call me. He SOLD her a few months later. I was soooo mad and hurt. He promised she went to a good home, but has lost contact with that person. Not too long ago I emailed and asked if he knew how to get a hold of the person. I wanted to check on her. He emailed me back and asked me if I planned on buying her back and keeping her in my backyard! He knows how pissed I was that he first of all went back on his promise not even giving me the option of coming to get her. Second of all made a profit off of a gift. Third sold a creature that meant a lot to me and my family. He promised me when I gave her to him for his son that she wold stay in our family. She was the best horse. She would have climbed in your pocket if she could. I am still mad at him to this day. As I sit here and type this I am crying and mad at him. I bought her thinking she would stay with us forever and she did not. I am a believer that when you bring an animal into your life it should be for their entire life. Sorry I have no advice except listen to the other posters. Hell how could I give you advice when clearly I am still having a hard time letting my own issues go. Good luck I am sorry that you were so disrespected. Sorry for my long story I am long winded today!

How are you going to support the thing and make it so you support yourself when crawling through? Are you planning to cut through the drywall and stick in the plastic trim? Attic stair, scuttles, and knee wall (doors) are notorious sources of air leaks and poor insulation in older homes. New designs incorporate insulation and air sealing, but there are some good retrofit solutions. The least expensive for attic stairs and scuttles is to build a foam board box with a lightweight bar running through the middle to act as a handle to lift it out of the way when removing it. The lower edge incorporates air sealing. There are also zipper bags that can be stapled into place to provide air sealing.