Measuring Vent Diameter in the Attic

If you dont want to get on the roof, you can go in the attic and measure the vent by measuring the circumference of the vent pipe and dividing this by 3.14. This will give you the diameter of the pipe. Or maybe you can read what the diameter is by looking at the pipe. With any luck its printed on the pipe. This method works if you can get access to all the vent pipes, and it assumes your roofer didnt use a larger lead flashing than he should of. Still the best method is to measure on the top of the roof.