I would like to know if it is possible to move roof vents. We are looking at
buying a new home and there are two roof vents at the front of the house and
one on the back.
What I need to know is if I can run the PVC horizontally to link up with the
vent in the back of the house. I spent some time looking on the web, but
can't seem to find an answer.
Any help would be appreciated.
(not a plumber) I know that from the fixture to the vent there are code
requirements as to how close the vent must be to the toilet, or to the
sink. Once the vent goes 'up' I am under the (possibly mistaken)
impression that you can run it any distance, e.g., from the front of
your attic to the back. If this is incorrect hopefully someone will
jump on this comment with the correct info.
Probably not if your talking plumbing vents. Check with a local plumbing
inspector he can tell you for sure. Then you have the issue of patching the
holes to match. Which will be darned near impossible.
I'd be interested to know * why * you want to move these items.
They are plumbing vents, are they not?
As SQLit points out, there are collateral issues.
If appearance is a problem for you, are the stacks painable?
Appearance is the problem and since we will be putting new shingles on the
roof, it won't be a problem to patch the roof before putting the new
shingles on. I'll call the plumbing inspector though and see what he says,
It depends on how close the vent pipes are to each other, how big the pipes
are, and what type of roof structure you have.
If you have vaulted ceilings, you probably don't have an attic space to
reroute the pipes through.
Vent pipes have size requirements depending on how many fixtures they vent.
If you have a few 1-1/2" or 2" vents penetrating the roof, you could
probably combine the vents into a single 3" vent instead. But, if you
already have multiple 3" vents, you're probably out of luck.
When I plumbed my house, I combined all my fixture vents into a single 3
inch "trunk" line in the attic. I then ran a single 3" vent through the
roof. Of course, everything has to be sloped downward so the air can flow
"up" and any water that finds it's way into the vent can flow "down"
(though technically, air also gets pulled "in" the vent as water flows down
A larger vent has more exposed area at the roof, so you might want to add a
"mushroom" cap on the top to keep out leaves, squirrels, etc.
Check out the plumbing forum at www.plbg.com to ask questions. There are
several professional plumbers there that can help out. You should also pick
up a couple of plumbing books to see how typical plumbing systems work.
Of course, as others have said, once you move the vents you'll need to
patch the holes left behind. I would assume you are planning on reroofing
the house as part of this project?
What you propose is certainly doable, if you're willing to invest the time
and money to make it happen.
The limiting factor on DWV pipes isn't the size or number of fixtures
it vents, but rather how big around it has to be to prevent frost-up
during the winter. a 4" vent will handle anything you're likely to
find in a normal house. What you might have a problem with is
reducing the pipe-size as you go down through the system.
I don't know what code says, though. Worst case, you can always
cluster the three existing stacks together, and wrap some
sort of cowling around them.
According to UPC, a 1-1/4" pipe can only vent one "fixture unit", 1-1/2"
pipe can vent 8 fixture units, 2" pipe can vent 24 fixture units, and 3"
pipe can vent 84 fixture units. The size must be increased if the vent pipe
is more than 40 feet long, and a toilet requires a minimum 2" vent.
("Fixture Units" vary from 1 unit for a bathroom vanity, to 4 units for a
So, if you have four 1-1/2" pipes penetrating the roof, a safe estimate
would be to assume each is maxed out at 8 fixture units (unless you want to
calculate exactly what fixtures are on each vent pipe). To combine these
into a single larger vent, you would need at least a 3" vent through the
roof (4 vents x 8 units = 32 units).
Realistically, a house with 2 full baths, laundry, and kitchen sink with a
dishwasher would total about 18 units. A single 2" vent would theoretically
be adequate for that case, but I would still opt for the larger vent.
There's no harm in going larger, but going smaller could cause a variety of
problems. As Goedjn mentioned, smaller vents are more likely to ice up in
cold climates (though based on the original issue of multiple small vents,
I doubt that's an issue in this case). A larger vent will allow better air
flow and is less likely to clog with debris.
Going "down" in the vent sizes is just like going "up" in drain sizes. Just
think in reverse. You should have no problem finding reducing tee's and
elbows to combine the smaller individual vents into a single large vent.
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