How to Install Roof Vent Guard? -- 2nd Try

Because no one has responded the first time around, let me post my question one last time before I give up:
I need to know the way to install a roof vent guard over a round roof- mounted vent fan.
The round roof-mounted vent fan has a screen covering the air outlet. But the screen has no frame to stiffen it. Consequently, squirrels push the screen away easily. They lived inside the roof for some time until I finially get rid of them. Now, I am sure that no squirrel is inside my roof any more. I need to keep any new comer away.
I want to install a square steel cage over the round roof-mounted vent fan. The problem is that I cannot find any instruction about installing it anywhere in internet (they only say that it is easy to install). Therefore, I am not sure if this is something that I can do. I don't want to nail it in place because I am afraid that I may add a way for water to leak inside the roof through the nails.
One thing that I want to point out is that I have a very low pitch roof. The roof doesn't have any shingle. It is covered with a thick layer of roll-roofing. I am not sure if this makes any difference or not. I want to mention about this in case this makes any difference.
Please tell me the appropriate way to install a steel roof vent guard. Thanks in advance.
Jay Chan
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Unfortunately there is no "standard" way to install such an item as there are many problems to overcome: what attachment points are available? what shape is the fan unit? what area is to be covered? is the fan unit installed on a curb? Do you have a guard or must you build one?
A photo may be useful, but it is probably one of those things that one needs to be creative in designing, building and installing the cage on the fan or on the roof. Experience and adaptability are requirements of the installer, anything we say over the internet is of little practical use if it doesn't suit your needs or the conditions you are working with.
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The roof vent guard that I intend to install is like the one shown in this URL:
http://www.gascoals.net/ChimneyCapsPipe/ChimneyCaps/RoofVentCovers/tabid/1276/Default.aspx
My round roof mounted vent is just like the one shown in the picture. It has a fan inside. The idea is to use the "roof vent guard" that is a steel cage to cover the round roof mounted vent. You can see from the picture that the flange of the roof vent guard has a serie of holes in it (other models from other web sites also have similar holes). This seems to suggest that I am supposed to nail it in place. I will need to give this whole idea a second thought because I am afraid that all these nails are going to give rain water a way to leak inside my roof.
I may just have to follow the other newsgroup member suggestion to stiffen the screen that is already there. I intend to remove the screen and see if I can stiffen it later today.
Jay Chan
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Jay Chan wrote:

How about replacing the existing screen with something more substantial? I bet the original was designed to keep out leaves, maybe insects, but yielded to the attacks of a tree-rat.
You could use the existing screen as a template to cut a replacement from hardware cloth, rebar, or similar.
Can you provide the name/model of the existing fan? That way we could look at the manufacturer's picture and maybe come up with some other ideas.
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wrote:

Sounds good. He mght also be able to attach the new screen to the old screen.
SEe what hardware stores sell for screen. What does one call the heavy screen with 1/2 x 1/2 inch holes? We used it on a back door with a window to keep a burglar from breaking the window and opening the door.

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hardware cloth is the 1/2 inch stuff
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I am likely to do just that. Thanks for the suggestion.
The steel cage that I originally wanted to buy to cover the round roof mounted vent has flange all around that has a serie of holes on it. I believe the steel cage (called roof vent guard) is meant to be attached to the roof using nails based on the fact that the flange of the steel cage has so many holes on it. This is just a guess. I just don't like the idea of shooting that many nails into my roof (this has rool roofing kind of like a rubber roof). I am afraid that I may end up making many ways for rain water to leak inside the roof. Therefore, I am thinking of stiffening the existing screen inside the roof vent instead of using a steel cage.
The existing metal screen is under the round roof vent cover. The screen is placed vertically, and is attached to vertical steel rods that is positioned around the round vent hole. The rods supports the round vent cover. Unfortunately, the screen is not stiffened by any flange around it. It is good enough to prevent leaves and insects from getting inside the roof. But it is not stiff enough for small animals like squirrels. A squirrel can simply push the screen aside and gets inside the roof.
Later today, I will remove the existing screen from the vent, and use it as a template to cut a sheet of heavy gauge metal screen. Then I intend to combine them together. The existing screen will continue serve as a way to keep leaves and insects away. The heavy gauge metal screen will be the backing of the existing screen in order to stiffen it. Seem like this will be the easiest way to do.
Thanks for the suggestion again.
Jay Chan
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Jay Chan wrote:

Good luck. I like your idea of combining the screens.
One further advantage: the roof won't look as weird as it would with that box-like screen add-on.
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Thanks for your suggestion of using the existing screen as a template. Yesterday (before the snow storm hit my area), I remove the existing screen as a template, and use it to cut a piece of heavy gauge metal screen. The wire in the heavy gauge metal screen is vinyl covered and should last very long. I cut the piece a bit taller than the air opening; I use the "extra" material as a kind of bar wire by cutting the extra material into pointy wires sticking outward and upward. This should discourage squirrels from touching the screen. This heavy gauge metal screen is very stiff. Now I am sure that squirrels won't be able to push through this screen.
I am glad that I have fixed it. Not only I can prevent squirrels from getting into my roof, but also I may have saved the motor in the roof vent fan. What's happened is that there was little margin between the original screen and the fan blades. When squirrels pushed the original screen inward, the original screen got tangled up with the fan blades. If the weather was hot, and the roof vent fan started working and the fan blades would get stuck, the fan motor would become damaged. Hopefully, the fan motor is OK.
Actually I am not 100% done yet. Because I have positioned the new screen a bit further away from the fan blade, the original screen is too short now. I will have to replace it with a long one. I will have to wait until the snow and ice has completely melted before I will continue. But for the purpose of keeping squirrels away, I am done.
Again, tahnks for your suggestion.
Jay Chan
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