"Walter Cohen" wrote in message
...
Thanks John.
Some have suggested NOT to use a hole saw but instead a jig saw or
sawzall.
Mostly because of tearing through roof shingles once it pokes through.
Thoughts on this?


I've done it both ways. I think the jig saw is a little more time consuming
and the hole may not come out as perfectly round as you like. You could
drill a pilot hole through the center from below and then go up on the roof
and start the hole using that center mark. However you do want to position
the roof cap flange so that it aligns with the shingles and can slide under
for best water protection.

As I said before, drill at a slow speed and take your time. If drilling
from below, when you start to see the the roof shingles stop the drill and
try to remove the wood by hand. If you can't at this point, drill a little
more until you can. You can then cut the shingles from above by hand with a
good knife or compass saw. Push a coat hanger through the pilot hole to
find the center on the roof.

I try to do it in this order when possible:

1. Drill pilot hole from below and push wire through hole.
2. Using pilot hole as a reference, position center of roof cap to align
best with shingles and keep pilot hole within roof section to be removed.
3. Drill hole with slow speed, high torque drill until you are through
roofing materials.
4. Remove roofing materials from hole saw.
5. Continue drilling hole saw through wood.
6. Set roof cap using roof cement as needed. Roof cement should go under
shingles and cap.

This way only one trip up to the roof is required. A five gallon bucket is
useful for carrying items at once.



Walter
"John Grabowski" wrote in message
...

"Walter Cohen" wrote in message
...
Due to logistical reasons in my attic I need to route the new bathroom
fan exhaust duct up through the roof instead of out the side wall. It's
also a shorter run if I go vertically instead of horizontally.
I'll be buying 4" aluminum ducting so when I buy a hole saw to cut the
roof hole do I buy one that's 4" round, 4 1/4", or 4 1/2"?

Anything else I should do or watch out for?



I use a 4 1/4" hole saw in my angle drill at slow speed. You don't want
to go too fast with a puppy this big.