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Small Cabin Forum / Cabin Construction / Steel roof venting options
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WILL1E
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# Posted: 9 Sep 2021 13:14 - Edited by: WILL1E
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Trying to figure out what's the best option for venting a metal roof. Plan is to use Pro-Rib steel panels from my local Menards.

Pro-rib offers precut/formed vented outside closure strips but they cost almost $10 per ~3' piece

They also offer a non-formed rolled version that get's it down to ~$2 per foot, however it does really clearly state if it has any adhesive to keep it in place. Shows a backing paper in the photo though, so i would assume it does.

So is that my only options or do i go with normal rolled ridge vent and just squish it under the steel ridge cap?

ICC
Member
# Posted: 9 Sep 2021 13:37 - Edited by: ICC
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Quoting: WILL1E
Trying to figure out what's the best option for venting a metal roof.


?? Those "inside closure strips" are meant to be used under the eve edge of the metal roofing when the roofing sheets are applied over sheathing (OSB, plywood). The foam is to keep insects from crawling up the ribs. No real ventilating going on.

Then there are "outside closure strips" that are meant to be used on topof the metal roofing sheets up near the ridge. The metal ridge cap goes over those to also keep insects and water out. More like an anti-vent.

How do you intend to install the roofing panels? What sort of roof assembly?

Nate R
Member
# Posted: 9 Sep 2021 13:54
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Honestly not sure how much you need to worry about venting the topside of the sheathing....

Shingle roofs, the topside is often vapor impermeable with some of today's roofing underlayments on it.

WILL1E
Member
# Posted: 9 Sep 2021 14:09
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Quoting: ICC
?? Those "inside closure strips"

It was a typo, fixed it. Yes, i need outside closure strips that are vented.

Plan was, going from outside in: metal roof panels, 30lb felt paper, plywood sheathing, 2x8 rafters, vent trays going from sofit to ridge, wool insulation and then vapor barrier.

ICC
Member
# Posted: 9 Sep 2021 14:17
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The other linked to Pro-vent material is to provide a screened vent at a metal ridge cap when the ridge is used as an exit vent for airflow that originates from the soffit line. It will also keep out most insects and blowing snow, but allows airflow.

Quoting: Nate R
Honestly not sure how much you need to worry about venting the topside of the sheathing....


Correct. No need to ventilate under the metal roofing when the metal is applied over a weather-resistant barrier that is installed over the usual roof sheathing. In some locations, there may be insects that like to make nests under the ribs or will use that access for mischief.

gcrank1
Member
# Posted: 9 Sep 2021 14:21
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With your loft you are going to have a peak, same on the other end; ie, 'cath ceiling'?
If so you can install a vent at the gable peak sized for your c.ft. to passive or power vent in the heat of summer.
At our place I used a 6" galvanized pipe with a 6"to 10" 'bell' to act as a funnel. With the room windows open the natural convection keeps the heat from stacking top to bottom and if needed I have a cheap 6" 'clamp-fan' to power out (they are available in 12vdc and 120vac). This worked quite well for is this past summer. We tended to use the window on the shaded side for input air.
A bigger hole would flow more; I used the old 6" stovepipe hole already there as proof of concept.

WILL1E
Member
# Posted: 9 Sep 2021 14:28
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Quoting: ICC
In some locations, there may be insects that like to make nests under the ribs or will use that access for mischief.

I was going to use foam inside closure strips at the eave ends for this reason. Should i not do that?

ICC
Member
# Posted: 9 Sep 2021 14:48
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I would only omit the inside closure strips if I was in an area that had no insects. Not too many places like that, though some of our desert areas here have few flying insects. I don't have them on a couple of sheds here. No issues. But we would always use them on residential and commercial.

WILL1E
Member
# Posted: 10 Sep 2021 07:54
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Quoting: ICC
if I was in an area that had no insects

Well WI is not one of those areas...the mosquito is our state bird !! But honestly up north around here bees can be a problem on cabins and i hate them with a passion, so the closure strips will be happening for sure!

littlesalmon4
Member
# Posted: 10 Sep 2021 11:03
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Those closures are a 4 pack so it is actually 12' of coverage.

WILL1E
Member
# Posted: 10 Sep 2021 11:13
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Correct.

toyota_mdt_tech
Member
# Posted: 10 Sep 2021 15:52
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Willie, I would put the metal over sheeting and use 30# felt or a rubber membrane under it would be the best. Follow mfg specs. The foam enclosures I used and it keeps bugs, bees out etc and blowing snow.

Follow mfg specs on screwing schedule.

Brettny
Member
# Posted: 10 Sep 2021 19:37
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They make special metal roof underlayment for this application and use with perlins. It's quite a bit more than tar paper but tar paper is not very water proof after a few wettings. (Dupont) Tyvex makes 3 different ones. I dont think you will find a quality metal roof underlayment at a big box store.

ICC
Member
# Posted: 10 Sep 2021 20:40
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Quoting: Brettny
but tar paper is not very water proof after a few wettings.

That is not true unless you are talking about tar paper (building felt) that has been left uncovered a long time.

When tar paper gets wet the fibers expand and actually make the paper more resistant to liquid water. And then when the source of the water dries up the paper dries to the exterior.

We have removed old siding from homes built in the early 1900's. The tar paper that was originally installed may be brittle and easy to tear but the tar paper itself will still cause water to bead up.

FWIW, FYI #1: since the first oil embargo in the 70's the amount of tar or asphalt in tar paper (building felt) has been reduced. Lab work proved that the amount of the petroleum product couls be reduced without causing ill effects.

FWIW, FYI #2: the naming changed at that time. It used to be that there was 15 pound and 30 pound (15#, 30#) versions. Those names came from the fact that the original specs called for the thinner to weigh 15 pounds for a square; a square is 100 sq. ft. The thicker was to weigh 30 pounds per square.

When the petroleum content was reconfigured the naming was adjusted. Today we have number 15 and number 30, #15 and #30. Many people do incorrectly call the #30, 30# (pound).

There are things I like about some synthetics. One, and to me a big plus, is that many of them have non-slip surfaces that are much better than building felt for walking on during construction. Even if slightly damp my boots have much greater purchase on the syn we have used for many years. It is also lighter weight, but is best handled by a larger crew. You can cover a big roof in a short time.

We all probably have favorite products. Mine is Titanium UDL. They make three grades and we normally used the best of the three. And where we are we can get it at Lowes as well as the roofing specialist. Even the highest grade.

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