proper roofing goop?


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Old 08-09-11, 06:12 PM
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proper roofing goop?

I知 going to be installing a metal roof cap (on the roof) to which the bathroom fan duct will be attached. I値l be needing to cut away a portion of the asphalt three-tab shingles there where the square roof cap upper side of its flashing will be slid underneath. I値l be securing with a few roofing nails in the flashing both upper and lower of the cap. My question concerns the proper caulk or cement to use over the nailheads and as well as between the bottom of the asphalt shingles and the metal flashing. I want to make sure I use what absolutely should be used for this particular job. I understand that to use/rely on just any old 途oofing goop or all purpose caulk or whatever is not a good idea, that there can be expansion/contraction and cracks/leaks can eventually occur if the wrong stuff is used. Any comments/advice appreciated.
 
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Old 08-09-11, 07:10 PM
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Henry's makes a pliable roofing compound. Use a spreader, 'cause it won't come off easily. Or you can get it in a caulk tube for ease of installation.
 
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Old 08-09-11, 07:32 PM
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Seems like Henrys has quite a few various sealants and cements for roofing. So it'd be nice to know which particular one it is I should get. 900
 
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Old 08-09-11, 08:16 PM
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I always see silicone used with good results.
 
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Old 08-10-11, 03:29 PM
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The 900 is excellent and will remain flexible. Silicone will die with sunlight, over time, but is a good sealant.
 
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Old 08-10-11, 05:56 PM
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NPC Solar Seal is good. But I rarely caulk under roof vents. If you do them right you don't need sealant, provided they aren't larger than normal. Of course, sealing nail heads is a given.
 
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Old 08-10-11, 07:00 PM
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The local place here doesn't stock the 900 or the NPC Solar Seal. They had this, and recommended it for my application: http://epmar.com/knowledge/brochures...alog_Sheet.pdf
So I guess this will be the goop I'll be using. Thanks
 
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Old 08-11-11, 09:51 AM
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Originally Posted by XSleeper View Post
I rarely caulk under roof vents. If you do them right you don't need sealant, provided they aren't larger than normal. Of course, sealing nail heads is a given.
Please note how on the installation directions for this particular roof cap it shows/describes using sealant along the edge(s) (top right of page, and step 7). Please comment... thanks

http://www.broan.com/ImageLibrary/br...s/99041929.pdf
 
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Old 08-11-11, 10:23 AM
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Thats exactly the type vent I used when I replaced all mine after moving here. That roofing cement like they show is really not needed in that large a bead. I put some on the top of flange just in from the edge of the shingle...then put bricks on top and sides to weight it down for a few days. More to keep the shingles from lifting or curling than for sealing.

I also cut the shingles for a nice tight fit, no big gaps at the top or sides, just enough to allow drainage down and off...maybe 3/16 inch? I'd much rather trust a good mechanical drainage than rely on any type of sealant.

I hope you also realize you shouldn't use the regular cloth duct tape to seal the ducts to the vents....you need to use the metal foil tape.

We don't have the 900 or the NPC here either...at least not anywhere I could find...pretty limited selections. I used a regular tarlike roofing sealant and it's been fine. I put a dot under the vent flange where I was going to nail..then nailed through it...then covered the nailheads.
 
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Old 08-11-11, 10:34 AM
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Okay thanks Gunguy for those tips. But dangit I already used the regular cloth duct tape to seal the duct to the fan outlet stub (up there in the attic in a tight pain-in-the-a** spot). Why is it so important not to use that and to use the metal foil tape?
 
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Old 08-11-11, 10:42 AM
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If you used regular "duck" type tape....it won't stand the heat or cold of the attic. They do make versions that are supposed to be better....but that's taking a chance IMO. How would you know if it came off?

The foil tape is designed for high and low temps and is moisture resistant.
 
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Old 08-11-11, 11:07 AM
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Originally Posted by sgull View Post
Please comment
I suppose they view it as added insurance against leaks. On such a small vent, you likely have a full shingle underneath the entire side of the vent, and you'll probably have only one shingle overlapping it on the side. If the shingle underneath extends as high or higherthan the top notch in the shingles you really don't have to worry about water blowing sideways off the vent andcausing a leak. But if you have 2 shingles on the side like they show, then yes it is probably a good idea to caulk, because the top 3" or so would be vunerable to water blowing sideways off the flashing, and getting in on top of the bottom shingle that is underneath the vent.

Some vents will also have a small rib on the left and right sides that helps to channel water down the side of the vent. Seems like those Broan vents are flat (w/no rib) if I recall. That could be another reason.

I'm picturing a small dryer vent that are roughly 8x8, not the large mushroom/lomanco vents.
 
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Old 08-11-11, 11:32 AM
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Originally Posted by Gunguy45 View Post
If you used regular "duck" type tape....it won't stand the heat or cold of the attic. They do make versions that are supposed to be better
I used a cloth-reinforced duct tape that says its a "professional premium contractor grade" and is described as
More aggressive adhesion characteristics than all-purpose duck tape
Thick cloth with more fibers for increased strength
Improved durability for indoor/outdoor use
 
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Old 08-11-11, 11:43 AM
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In those instructions (link in post #8 here) in step 5 it describes cutting/trimming of the shingles and shows those measurements in the diagram. I'm not really clear on how those measurements are meant correspond to the lines shown they they seem to point to. What might be a more specific explanation there of how exactly they're suggesting the shingles be trimmed?
 
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Old 08-11-11, 01:45 PM
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Well...if you can at least see it...I'd suggest checking it every year or so to see if it's holding up. They can print anything on the label they feel like. I could say my advice is endorsed by contractors everywhere...doesn't make it true.

I think what the mean for the trimming is based on the width of the flange. Put the vent in position over the existing hole (or where the new one will be)...trace around the edge..then measure in a specific amount (prob the width of the flange). Notice they say "shingles will fit snugly around hood"? Thats what I did...only left a slightly larger gap, since I didn't seal as they said. Tight to the hood at the top (you could even trim it in a semi-circle)...slight gap on the sides.
 
 

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