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Question about roof top flashing around chimney

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by tradergordo, Jul 4, 2006.

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  1. tradergordo

    tradergordo Minister of Fire

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    Loc:
    Phoenixville, PA
    I am in the process of installing a supervent chimney. It has a pretty standard looking flashing for the roof. The instructions say to remove the shingles first from the area under the top half of the flashing, nail the top part of the flashing down to the roof, replace the shingles to cover the top half, and let the bottom half come over the shingles. This is all very standard, and looks just like the other 3 flashings up on my roof. But my question is this - with the other flashings on my roof (from things like the furnace vent pipe) the installer/builder did NOT nail down the lower exposed half of the flashing. This is because you generally don't want to put holes in your roof unless you are covering them with shingles or you will eventually have leaks.

    But the directions from supervent tell me I am supposed to nail down the flashing ALL the way around including the lower exposed half. It says to use neoprene washers or silicon sealant on the nails. I don't want to deviate from the manufacturers instructions, but I was just wondering what other people have done and if you did put fully exposed nails though your roof did you have any problems with leaks? They also don't say what type of nail to use and I'm wondering if the galvanized roofing nails that I have been using are too short to go though two layers of shingles, the flashing, and into the roofing material.

    I guess not nailing it down fully could cause the chimney to have some play which would not be good, and it could also give enough room for bees to fly into the catheral box below the flashing and build a nest in there, which I suppose could potentially catch fire?

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  2. Shane

    Shane Minister of Fire

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    Here in Wyoming we have hellacious winds and little rain so I ALWAYS nail down my flashings. I always seal the perimeter of the flashing and nail holes with good ol roof tar. You don't want wind to blow up under the flashing and rip it up. Or the more common problem of rain and snow getting on the underside of flashing then it freezes. You'll get more leaks that way than with some tiny nail holes in your roof.
  3. Michael6268

    Michael6268 Feeling the Heat

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    Grafton NH/Upper Valley
    Ditto with Shane's response. Roofing tar under the entire perimeter of the flashing and on top of the exposed nail heads. Some people use silicone on the nail heads saying it holds up to the sun/heat better.
  4. elkimmeg

    elkimmeg Guest

    All good advice tar down the flashing flange and nail it down 4 corners. But not at the start.

    The bottom rows of shingles go under the flashing flange. That's right the bottom is exposed After the full 5" exposure goes under then the next rows are cut to the side of the flange ( meaning the extent up to the point where the flange and pipe begin to assend up. Also do not be concerned about being 100% tight a 1/4 to 1/2" space there is ok), finally the top rows goes over the flange. Just after you finish the bottom row or rows under then tar it down and nail the corners I also tar under each row of shingles as they extend onto the flashing flange
    I I find it best to get a tube of roofing cement and use a caulking gun. Finally when finished dab the two bottom exposed roof nail heads with roofing cement or silicone caulk. The key here is to envision the flow of water.
  5. tradergordo

    tradergordo Minister of Fire

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    Phoenixville, PA
    Thanks everyone, very helpful advice.
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