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Electrical Dude 11-22-2009 12:01 PM

How do I install an attic fan on a gravel/tar roof?
I am in the process of installing a standard attic fan for a customer who has a gravel and tar roof. I have installed hundreds of fans and I am well aware of the risks. The surface is almost flat which means... no gable! This is the only option and installing a flashing on the roof is our final choice. Please respond only with tips on how to do it on the specified roofs, all other options have been explored.



meltdowndave 11-22-2009 04:11 PM

I'm not quite sure that I understand the situation entirely, but what about building a small box and mounting the fan to that? Then you could tar around the box and then flash/counterflash.

You might want to make sure this isn't in a low point in the roof or ponding might present a problem for your freshly sealed hole.

tinner666 11-22-2009 07:00 PM

Use a gravel bumper and clean the gravel back about 18"-24" on each side. If you tear into the felt anywhere, keep bumping to clear a larger area. Build your box 1" smaller than the fan housing, install the curb, then using a mod-but torch, heat and bend in at least 2 layers of mod-bit. Pay special attention to the corners, and run the mod-bit to the top of the box. Install the fan housing, which should cover the mod-bit about 2". That's your counter-flashing. Touch up any edges with Karnack Ultra19, I believe. Read the can to make sure it's compatible with the APP mod-bit you used.

tpolk 11-22-2009 07:03 PM

nicely done Tinner

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