roof hole

[Malak]

I just got all my chimney crap yesterday, and when it says to maintain a 2" clearance to all combustibles does that mean that I literally make the roof hole 2" bigger than the OD of the pipe i.e. 4" in diameter bigger?

thanks

 

[Shortstuff]

That's correct. My Duravent Pro is 3-5/8" OD and it requires at least a 1" clearance to combustables, but I doubled all the clearance requirements, so I made mine 2" all around as you can see below.

Steve

 

[Nic36]

If you cut a hole in your roof using the outline of the big hole in your roof flashing, it should be wide enough to meet the 2" requirement once the pipe is installed. Mine was. Just make sure the location of the hole is where it needs to be, or else you may have to cut it bigger.

 

[jeff6443]

When they cut the hole in my roof for my v c dutchwest I said oh my god . Installed in june I go in the attic everytime it rains looking for a problem. Only cuz I paid for the install . I sell dead fish not too handy indoors . 2 to 3 inch around pipe . The guy said this how he would do it if it was his house .

 

[Malak]

I wanted to mention for the other newbies like me that the hole must
be elliptical i.e. oval! Luckily, I thought of this the day before. Because
when you tilt a circle relative to a vertical column it becomes closer
at the top and bottom than at the side.

The formula is: pipe diameter/COS(roof angle) X 2

So, for 6" pipe, 2" clearance, and 30 degree roof: 14" X 12" minimum.

I did a 15" X 13" to be safe and glad I did!

It turned-out surprisingly well. Whew!

You can use a drywall saw with no problem. Don't put your weight
on the same plank you are cutting. Use a pilot hole from the inside
to put a center screw up thru the roof and make a cardboard template
with a center hole. So all I did was put the template on the screw
sticking out and trace and cut! Viola!

 

[billb3]

I'll have to remember never to put an elliptical pipe in a round hole.