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-   -   Running vents under metal roofing. (http://www.diychatroom.com/f9/running-vents-under-metal-roofing-199512/)

Johnny Oregon 04-17-2014 03:14 PM

Running vents under metal roofing.
 
So we are going with the standing seam, hidden fastener metal roofing on our manufactured home. We are leaving the existing 3 tab on the roof and overlaying with furring strips of 2x4 or 1x4 depending on this question:

It is my goal to have no roof penetrations. To accomplish this I need to deal with three 1 1/4" plumbing stack vents and two bath fan vents.

One thought is to use 2x4 furring and run the stack vents along the roof in the space created by the 2x4 and exit into the ridge vent. Obviously if I use a 1x4 or no furring strip, this wouldn't work.

Question is how to deal with the bath fan? I could maybe have some kind of low profile sheet metal duct built to lay in the cavity and exhaust into ridge vent. Seems like that could lead to moisture-laden exhaust running under the metal panels. Am I worry about this too much considering there would be an 1 1/2" airspace and asphalt in the void?

Other option might be to try to pull the duct through the very limited "attic" cavity and exhaust it out the soffit.

Thoughts?

joecaption 04-17-2014 03:43 PM

Not a great plan, stick with the proper roof jacks made for metal roofing.
Your sewer vents work by the air passing over them creating a negative pressure to suck out the gasses.
For a bathroom vent to work it needs a full 3 or 4" port, restrict the flow and it's useless.
Have you priced out what the roof is going to cost?

Johnny Oregon 04-17-2014 04:08 PM

Quote:

Originally Posted by joecaption (Post 1338482)
Not a great plan, stick with the proper roof jacks made for metal roofing.
Your sewer vents work by the air passing over them creating a negative pressure to suck out the gasses.
For a bathroom vent to work it needs a full 3 or 4" port, restrict the flow and it's useless.
Have you priced out what the roof is going to cost?

Thanks for the input. I hear what you are saying on the vents and air flow. Odd thing is, since I've looked into metal roof I've seen three or four manufactured homes in our area with no roof vent penetrations at all.

I hadn't planned on restricting the size of the bath vent...just reconfiguring the shape. Going with more link an oblong or rectangular vent with same surface area.

mako1 04-17-2014 04:09 PM

In addition to what Joe said.If furring your metal roof on top of your shingles,the closure designed for you metal roof will not work.

Johnny Oregon 04-17-2014 04:32 PM

Quote:

Originally Posted by mako1 (Post 1338499)
In addition to what Joe said.If furring your metal roof on top of your shingles,the closure designed for you metal roof will not work.

What do you mean by "closure"? Nothing would change on the ridge vent? Flashing may have to have a longer to leg to make up for the added height of the furring.

mako1 04-17-2014 05:11 PM

There is a foam closure that goes between your siding and roof deck at the eaves.

Johnny Oregon 04-17-2014 05:34 PM

Quote:

Originally Posted by mako1 (Post 1338520)
There is a foam closure that goes between your siding and roof deck at the eaves.

I guess I'm not following. The siding and roof deck already exist on the home. The instructions for this metal roofing list no foam closures. It goes roof deck (or furring strip)...fascia and eave trim...roofing panels....edge cap and ridge vent.

Are you talking like the foam wiggle board used on corrugated roofing? I'm talking standing rib roof here.

OldNBroken 04-17-2014 05:56 PM

Not sure why you are concerned about the penetrations in the roof. The ones you are describing simply need a dektite to seal it up. Sounds like a lot of work for little benefit and possibly causing unforeseen problems.

What mfr and system?

mako1 04-17-2014 06:04 PM

I mistyped.The foam closures go between the roofing and the deck.I understand your talking about standing rib .The type I have installed still had foam closures.

Johnny Oregon 04-17-2014 06:06 PM

Quote:

Originally Posted by OldNBroken (Post 1338540)
Not sure why you are concerned about the penetrations in the roof. The ones you are describing simply need a dektite to seal it up. Sounds like a lot of work for little benefit and possibly causing unforeseen problems.

What mfr and system?

Obviously I'm concerned about leaks at penetrations! 20 years in the RV industry taught me if there is a hole in a roof, it's a good chance it will leak eventually!

I agree maybe I'm making too much of it but since I've seen a couple homes in the area with no pentrations, I know it can be done!

Taylor and AEP are the two systems I'm looking at.

OldNBroken 04-17-2014 06:56 PM

If you are on the rusty side of the state, might try Bryer or CustomBilt. They both have a 1750 panel and are in that area.

Best way to do those boots is embed them in a good butyl with a screw every 1 to 1 1/4" around perimeter and hose clamp at the top. Will last the life of the roof if done properly. We do them on flat metal roofs all the time with no problems

OldNBroken 04-17-2014 06:57 PM

Hold on, RV industry? Ima guess Hermiston area then.

Do I win?

Johnny Oregon 04-17-2014 07:02 PM

Not quite...Eugene area!

OldNBroken 04-17-2014 07:19 PM

Damn, I was way off

1985gt 04-18-2014 12:25 PM

The RV industry also just plunks a hole in the roof adds the vent and goops it down. IF done the proper way like OldNbroken said the deck tite boots last a very long time. The only thing we do that may be over kill is put water stop on the boot around the pipe then clamp it.

Venting moisture inside of a space is a bad idea. That moisture will run down the underside of the panels and cause issues.

If furring the deck you will need a longer drip edge and possibly rake trim. Also I've never installed a standing seam panel with a foam closure except on the hips and ridges. even then you can do it with out needing them.


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