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Joe (Joe)
Moderator
Username: Joe

Post Number: 797
Registered: 07-2006


Posted on Friday, June 21, 2013 - 09:09 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

You can use 30 lb. felt as a separator between the metals. If water isn't going to contact the metals inside the sleeve, there probably won't be a reaction anyway.
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Old_school (Old_school)
Senior Member
Username: Old_school

Post Number: 995
Registered: 01-2009
Posted on Thursday, June 20, 2013 - 08:38 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Joe, that could be done, but you would want to separate the metals from each other. I suppose that could be the I and W, but that is going to want to melt when the heat is applied to solder it.
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Joe (Joe)
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Username: Joe

Post Number: 795
Registered: 07-2006


Posted on Thursday, June 20, 2013 - 09:36 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

You could possibly make a copper cover for the ductwork and solder the counter flashing to it.
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Old_school (Old_school)
Senior Member
Username: Old_school

Post Number: 994
Registered: 01-2009
Posted on Tuesday, June 18, 2013 - 06:22 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

That works!
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Timtrain35 (Timtrain35)
Junior Member
Username: Timtrain35

Post Number: 17
Registered: 03-2011
Posted on Tuesday, June 18, 2013 - 09:31 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Old School, we're thinking along the same lines. I figured fabricating all metal work using 24 gauge G90 stock. However, instead of sealant, we will probably go with pressure sensitive EPDM flashing membrane. We'll also use the IWS for a belt and suspenders approach.

Joe, the duct work is coming straight out of the attic, straight through the slate roof. It is connecting the unit in the attic space with the unit on the flat roof the slate roofs drain on to. The slate roof sections are not that long from eave to ridge, maybe 30' tops.

At this point, it's just a bid. If we get the work, i'll try and post some pics.
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Joe (Joe)
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Username: Joe

Post Number: 794
Registered: 07-2006


Posted on Tuesday, June 18, 2013 - 12:48 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

How high will the duct work stand off the roof?
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Old_school (Old_school)
Senior Member
Username: Old_school

Post Number: 993
Registered: 01-2009
Posted on Monday, June 17, 2013 - 06:07 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Just use galvanized step flashings and a termination type of counter/flashing. Fasten down the slates on the roof and then screw the termination type counter/flashing to the duct work. Caulk the kick out with a good grade of caulk and it will last for a long time. Some of the guys might disagree with this, but I would consider installing some Grace Ice and Water shield to the roof and to the duct-work before the step flashings are installed. This will act like a gasket when you screw the counter/flashing to the sides of the duct work. It will also stiffen it up a bit. Good luck with that one.
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Timtrain35 (Timtrain35)
Junior Member
Username: Timtrain35

Post Number: 16
Registered: 03-2011
Posted on Monday, June 17, 2013 - 11:18 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

It's horizontal. The top and bottom are the (relatively) easy part. It's the sides that concern me. It's not like masonry where you can step and counter flash, it's metal, and that's the rub.
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Old_school (Old_school)
Senior Member
Username: Old_school

Post Number: 992
Registered: 01-2009
Posted on Friday, June 14, 2013 - 06:24 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Is it going through vertically or horizontally? If it is vertical, you can treat it just like a chimney. If it is horizontal, you will have to make some type of diverter at the top to kick the water to the left or right of both.
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Timtrain35 (Timtrain35)
Junior Member
Username: Timtrain35

Post Number: 15
Registered: 03-2011
Posted on Friday, June 14, 2013 - 03:13 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Greetings all. We are being asked to flash some somewhat large duct penetrations into an existing slate roof. Listed below are some particulars about the project;

- Existing slate roof is roughly a 6:12 that drains onto a PVC flat roof.
- Duct work is designed to fit in between the existing rafters and is roughly 16" wide by 3' long.
- Duct work is lined (insulated from inside) and will be fabricated from light gauge galvanized.

Lost of things to consider on this one including, but not limited to;

- Potential for dis-similar metals in contact with each other.
- How to effectively and economically counter flash.

We've kicked around a lot of ideas in the shop, but I am curious how you all would approach this. Thanks in advance.

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