Nailing down a roof vent

Posted by Jon Danniken on October 5, 2009, 1:44 pm

Hello,

I am repairing a small section of my three-tab composite roof, and
installing a ducted roof vent for my bathroom fan.

What is puzzling me is that in addition to the two holes at the top of the
roof vent (which will be covered by the top course of shingles), there are
also two holes at the bottom of the roof vent.

If I put nails into these holes, they will be exposed, which is something
that I know should be avoided.

Here is a picture of the roof vent:

http://jonnycats.home.comcast.net/~jonnycats/RoofVent.jpg

I'm hoping that the people who make the roof vent know what they are doing,
but what exactly am I supposed to do here?

I'm guessing I am supposed to run the lower course of shingles to where they
are butting into the left and right hand side of the section of the vent
that rises up from the bottom plate (flange), so that the nail/nail holes
are covered by them.

In other words, should the shingles (represented by the mustard colored
overlay) cover the flange as in this picture?:

http://jonnycats.home.comcast.net/~jonnycats/RoofVent03.jpg

In all of the other roof vents that I have seen, the entire width of the
bottom end of the vent flange is treated like a shingle, and is just left
exposed without any holes or exposed nails, which is why this configuration
is puzzling me.

Thanks for any help on this,

Jon

Posted by RicodJour on October 5, 2009, 2:10 pm

wrote:

> Hello,
> I am repairing a small section of my three-tab composite roof, and
> installing a ducted roof vent for my bathroom fan.
> What is puzzling me is that in addition to the two holes at the top of th=

> roof vent (which will be covered by the top course of shingles), there ar=

> also two holes at the bottom of the roof vent.
> If I put nails into these holes, they will be exposed, which is something
> that I know should be avoided.
> Here is a picture of the roof vent:
> http://jonnycats.home.comcast.net/~jonnycats/RoofVent.jpg
> I'm hoping that the people who make the roof vent know what they are doin=

> but what exactly am I supposed to do here?
> I'm guessing I am supposed to run the lower course of shingles to where t=

hey

> are butting into the left and right hand side of the section of the vent
> that rises up from the bottom plate (flange), so that the nail/nail holes
> are covered by them.
> In other words, should the shingles (represented by the mustard colored
> overlay) cover the flange as in this picture?:
> http://jonnycats.home.comcast.net/~jonnycats/RoofVent03.jpg
> In all of the other roof vents that I have seen, the entire width of the
> bottom end of the vent flange is treated like a shingle, and is just left
> exposed without any holes or exposed nails, which is why this configurati=

> is puzzling me.
> Thanks for any help on this,

There are a number of ways to do it, and the picture is one of them.
Another way is to use some metal roofing screws with the rubber washer
under the head, or you could use some self-sealing membrane under the
vent so if water did get by the nail head it wouldn't follow the shank
down to the wood sheathing.

Here's another way to do it if you are replacing a section of the
roof.
http://www.sgsconstructions.com/yahoo_site_admin/assets/images/DSC01208.142=
124105_std.JPG
Do not use roof cement to glue down the shingles over the lower
section of the flashing as that will trap water. I don't particularly
like covering the lower part of the flashing as any water getting by
the shingles above is directed under the shingles below, and that's a
bad situation. Here's a variation that I like better (and the
drawing, too):
http://farm4.static.flickr.com/3392/3205874325_6577ab58f7.jpg?v=3D123229318=
4

Frankly, though, most roofers install the vent flashing with the
bottom edge exposed and just put a dab of roofing cement or silicone
caulk on the nail head. Generally works, but since you're doing it
yourself, and hopefully not settling for a "generally good" job, go
with the belt and suspenders approach - a piece of self-sealing
membrane below the vent and under the shingles where you'll be
nailing, and then the gasketed screws or roofing nails with sealant
over them.

R

Posted by Jon Danniken on October 5, 2009, 9:05 pm

RicodJour wrote:

> There are a number of ways to do it, and the picture is one of them.
> Another way is to use some metal roofing screws with the rubber washer
> under the head, or you could use some self-sealing membrane under the
> vent so if water did get by the nail head it wouldn't follow the shank
> down to the wood sheathing.
> Here's another way to do it if you are replacing a section of the
> roof.
>

http://www.sgsconstructions.com/yahoo_site_admin/assets/images/DSC01208.142124105_std.JPG

> Do not use roof cement to glue down the shingles over the lower
> section of the flashing as that will trap water. I don't particularly
> like covering the lower part of the flashing as any water getting by
> the shingles above is directed under the shingles below, and that's a
> bad situation. Here's a variation that I like better (and the
> drawing, too):
> http://farm4.static.flickr.com/3392/3205874325_6577ab58f7.jpg?v=1232293184
> Frankly, though, most roofers install the vent flashing with the
> bottom edge exposed and just put a dab of roofing cement or silicone
> caulk on the nail head. Generally works, but since you're doing it
> yourself, and hopefully not settling for a "generally good" job, go
> with the belt and suspenders approach - a piece of self-sealing
> membrane below the vent and under the shingles where you'll be
> nailing, and then the gasketed screws or roofing nails with sealant
> over them.

Thanks Ricod, I appreciate it. I looked around at a few other installations
today, and I did indeed see most of them with exposed (but caulked) nails,
and the full bottom width of the flange exposed.

I'll go ahead and use a little goo on the nailheads on the flange.

Thanks again,

Jon

Posted by Mike rock on October 5, 2009, 7:39 pm

> In all of the other roof vents that I have seen, the entire width of the
> bottom end of the vent flange is treated like a shingle, and is just left
> exposed without any holes or exposed nails, which is why this configuration
> is puzzling me.
> Thanks for any help on this,
> Jon

Here is an excellent video on how to install a vent on a roof. I
followed this when I had to put in a range hood vent.
http://www.youtube.com/watch?v=gee3itzjOG0

Posted by Jon Danniken on October 5, 2009, 9:16 pm

Mike rock wrote:

> Here is an excellent video on how to install a vent on a roof. I
> followed this when I had to put in a range hood vent.
> http://www.youtube.com/watch?v=gee3itzjOG0

Aye, thanks Mike, that's a great video. I see he used some nails on the
bottom edge of the flange, and just put some caulk over them.

Jon

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