Ridge vent for metal roof

[Alan Gage]

Hope to set the last of the trusses this week and finish up sheathing this weekend. I'm planning on a standing seam (hidden fastener) roof and wondered about my options on the ridge vent. Talked to my building supplier and he said most people have just been using the metal ridge cap with what looks like a plastic brillo pad strip underneath it to keep out bugs or any large debris that tried to blow in but still allows air movement.

I worry about wind driven snow and rain getting under the ridge cap in that situation and wonder if I shouldn't go with something more like these:

http://www.airvent.com/homeowner/products/ridgeVents-shingleVent.shtml

http://www.cor-a-vent.com/v600.cfm

As I understand it installation on a metal roof will be a bit trickier since I'll need to fill in the "valleys" between the ridges to give the vent something continuous to sit on.

I'll talk more to my supplier next week when I order the roofing and see what else they offer but I was hoping from some input from others who have BTDT on what they've done/seen.

Cimate zone is 6 (NW Iowa) where we get quite a bit of snow, our fair share of rain, and lots of wind. House is 1000 sq. ft. single story, hip roof (4/12 pitch) and somewhere in the "super insulated" category I guess. If I remember the ridge will be about 10' long. Will have continuous soffit vents. My building site is not very protected from the wind.

Thanks,

Alan

[dug]

I put on a metal roof (not standing seam) and they didn't offer a ventilated ridge cap either, they said just to leave out the foam closures on the ridge cap. I attached screen and hardware cloth across the gap (about 2 inches) at the peak and did as they suggested. I am a little apprehensive, we'll see how it works out. I would be more apprehensive with less than the 12/12 pitch I have.

[Arky217]

Alan,

I'm at the point of ordering my roofing as well and I've also decided to go with the standing seam panels. I'll be using McElroy Metal's Meridian panels. They have a flat flange along the male seam side with slotted holes for mounting instead of separate mounting brackets.

I too have puzzled over the venting arrangement at the ridge. It seems to me that the 'brillo type' ridge vent material would just inhibit the air flow too much. (By the way, the manufacture has  also told me that, compared to a clear opening, it does inhibit the air flow quite a bit).

Another thing I've puzzled over is the way they recommend screwing the bottom of their 'Z closure'  piece tight to the top of the panel and then the ridge trim to the top of the 'Z closure'.

It just seems to me that after you screw the eave end of the panels down tightly with gasketed screws (as is really needed to withstand wind uplift), and then screw down the ridge end tightly as well, that you are effectively locking the panels down tight at both ends. This would seem to defeat the purpose of the slotted panel mounting holes to allow the panels to move with heating/cooling expansion.

At this point I think I'm going to do the following at the ridge:
- Cut the plywood back from the peak 1.5" on each side for a 3" vent opening.
- Order the panels the length from 1" down from the plywood at the peak to 1" overhang at the eave. This leaves 1" of plywood above the top of the panels.
- Cut aluminum screen into 5" strips and staple across the vent opening into the exposed 1" of plywood on each side.
- With 1/8" stainless steel rivots, attach the ridge trim to the top of each seam about 1" back from the hem of the ridge trim.
- I might possibly put a few more screws at along the top of the panel, but if so, I would drill slotted holes for them like the mounting holes on edge of the panels and fasten them just slightly snug like the panel edge mounting hole screws.

This should give good venting and since the ridge trim extends 8" from the peak, it would provide 7" from the top of the panels to the hem of the ridge trim which should be plenty to prevent blowing rain from reaching past the top of the panels (especially on my 6/12 pitch).

The only thing I foresee that might be a problem is wasps building their nests under the ridge trim. I'm not sure what to do about that if it turns out to be a problem.
(Possibly wedge a rolled up piece of screen between the panel and the ridge trim ?)

Any suggestions for a better arrangement ?

Arky

[Don_P]

The eave of a standing seam roof is crimped over an eave trim but is not secured to it... in other words it can float at the lower end of the pan if needed.

[davidj]

We have a standing seam roof with a maybe 2" gap in the sheathing and a 6"x6" ridge cap.  Hardware cloth (I think 1/8") is used to keep insects etc. out.  We had a winter without roof insulation so any water entry would be reasonably obvious and I didn't see any.  However, we're pretty sheltered by trees and geography, and I would have been avoiding the cabin during any major storms.  But most of our precipitation is snow, which I would assume is more likely to find a way in, and I didn't find any staining of the plywood after the fact.

Also, given the space is vented, a little bit of water entering very occasionally probably isn't a big deal - it's unlikely to be enough to get through the insulation and start messing up the ceiling, and it should dry out in a day or two.

[Alan Gage]

Looking around this morning and I found this:

http://www.mwicomponents.com/univent.htm

That's the brillo pad stuff and they claim independent testing has shown it kept out wind driven rain and snow. No specific test information though, just basic results. That place is, amazingly enough, only about 45 minutes from me so maybe I'll go talk to them in person one of these days.

Maybe it does do a decent job keeping stuff out. Must restrict airflow too though.

Alan

[suburbancowboy]

I am at the same point you are.  We will be finishing putting on the osb and putting on the metal roofing this weekend.  The place where I got the metal roof recommended the brillo pad vent so that is what I purchased.  Hopefully it does the job.

[Dave Sparks]

I'll try and find the plastic stuff we used. We get lots of blowing rain and snow and I go up there every year (6 years old) in a storm and the 2 inch ridge is bone dry.  It is a black fiberglass mesh under the 6 x 6 ridge cover. Easy to do later also.

My comment about this material is that I think it is too good and does not move enough air.

[Dave Sparks]

The Cor-a-vent moves the most air and the Cobra vent has the best chance of stopping blowing rain.
That is from my research 6 years ago.

[considerations]

I have a 12/12 pitched roof sheathed in OSB, then felt paper, then metal.  I also have a metal ridge cap, underneath which is a strip, about a foot wide of black maybe plastic....like a giant version of what one scrubs kitchen pots with.  I really wondered about leaking, as we get a lot of heavy rain driven sideways. 

I moved in prematurely, and although the roof is insulated, I did not put dry wall up, only stapled up large sheets of clear plastic to ward off the breeze and cold.  The good news is that I can clearly see the apex of the roof from the underside and the water is not getting in under the ridge cap.  We also had a couple good heavy snows last winter, and still no sign of water.

Water in the roof was one of my big concerns, but it seems that this "breathing" roof works.  Now, as for bugs, well they get in, but I suspect from many sources, not just the roof, and I cannot specifically blame it on the ridge "barrier"....I've learned that there are varieties of insects that specialize in wintering over in your roof insulation. Clear plastic can be most instructive...like an ant farm.