How to vent eaves if no overhang, metal roof, Texas?

Roofing Business Talk
1

I’d like to replace my shingle over 5/16" OSB (excellent
condition, but cheap materials) roof with a standing seam
metal roof.

The “attic” interior is inaccessible, just 18" high at
the ridge, down to nothing high at the eaves. There is
no eave overhang; the roof stops an inch past the
vertical plane of the exterior wall. This is a new
manufactured home, so I guess I don’t need to have
overhang and gutters to keep water from the foundation,
because I don’t have a foundation.

I’m willing to spend good money now to minimize costs,
both roofing and cooling (it gets warm in Texas) over the
next 30 years. I’m assuming costs of energy will go up
dramatically over that time span, as will inflation in
general. So best to do it now, for maximum benefit,
lowest cost, over time.

Currently the tiny “attic” is vented through the roof
with low profile cheap plastic vents – about 12 of them
in all, six of them high up near the ridge, six of them
low down. The roof is a simple gable, 3:12 pitch, 76 ft
long over a 16 ft wide home, so should be about 8.5 ft
from ridge to eave on the slant. That should be about
1290 sq ft of roof.

If I stayed with asphalt shingles, then this would be a
natural for SmartVent on the eave inlet vents.

Main question: But how in tarnation can I get inlet
ventilation with a metal roof, when I have no eave
overhang or soffits?

Related questions: What sorts of underlayment, vapor
barriers, radiant barriers (above the deck, blown in
chips over the blown in fiberglass, …?), air gaps
below the metal, and such would you recommend.

I supposed the outlet ventilation would be one of a
ridge vent or a row of dormers. I am concerned that
a ridge vent will impede the airflow too much.

http://www.roofing.com/images/topics/7938/img_1243981731.jpeg

2

The structure pictured most likely has 2"x2" rafters/trusses with less than a 4" heel height.

After insulating there is not much room for rafter vents.
Poorly designed for intake ventilation.

3

[quote=“-Axiom-”]The structure pictured most likely has 2"x2" rafters/trusses with less than a 4" heel height.

After insulating there is not much room for rafter vents.
Poorly designed for intake ventilation.[/quote]

Most likely you are correct.

The current “intake” vents are low profile through the roof vents that are 2 or 3 feet up from the eaves. That’s probably about as low as they could put them and have any chance of clearing the blown in fiberglass insulation, assuming that is that the placement of those vents demonstates any engineering forethought at all.

If so, then I must continue to use through-the-roof vents, period.

From what I can tell, roof penetrations are alot easier on asphalt tile roofs than on raised seam metal roofs.

If that is so as well, then I should probably give up on my idea of putting a metal roof on this, and just replace the asphalt shingles after each hail storm. Perhaps I could add a few more through the roof passive vents, and perhaps the next time I buy shingles, I can get ones that reflect the sunlight a little better (until they get dirty.)

The main problem left with that approach is that if and when a leak does occur, given the inaccessibility of the “attic”, it could be years before I notice the mold and structural rot. Only when some damage pokes through to my living space will I see it.

Guess I’d just better get back to work on getting richer, so I can buy a fancier house. That of course won’t be trouble free – just different problems. There’s no free lunch.

My key remaining question given the above – are roof penetrations (such as for passive vents) really more difficult on raised seam roofs than on asphalt? Difficult in two ways: greater risk that it gets done wrong, and quite a bit more labor expense for anyone who is good at that work.

If there was a reliable way that wasn’t more than 2x more expensive to put in roof penetrations on a raised seam roof, then I could just throw a bunch of passive vents at it, high and low, like I have now on the asphalt shingles.

4

For a metal roof you would want the ridgevent that goes with the metal roof you choose.

5

Yes. But that just covers the air going out.

What do I do for the air intake? I’m guessing that each penetrating roof passive vent would cost a few hundred dollars of labor on a raised seam metal roof, if done correctly. It would take a dozen or two of them to get decent coverage.

But my guesses could be wildly off the mark.

6

Your intakes will most likely need to be a custom solution executed by your roofer of choice.

Buildings such as those pictured are meant to be inexpensive, not to last…
They are not all built the same, they tend to have many issues, and most roofers don’t want to touch them.
It probably has 3 ply 3/8" decking on it also.

Spending the money to put a metal roof on such a building is like putting lipstick on a pig…

Someone will do it though and if you want it done right with good ventilation be prepared to spend a decent percentage of the cost of the building.

Every building like this I have worked on needs the ventilation and the insulation fixed.

The last one like this I bid to repair the insulation, ventilation, and the roof was over $600/sq.
This was for an asphalt roof…
The intake on that particular building was some sort of perforated j-channel, it didn’t work and there was ice all down the exterior wall, and water running down the interior wall.

I didn’t get that bid and that is just fine by me.

Some things just can’t be economically fixed, throw enough money at it and anything can be fixed…
How much money are you willing to throw at this?

7

$500 to $1000 per square, if both myself and the roofer think the results will be nice.

Given current pricing, I am willing to overpay.

I spend most of my time studying the economy, and I am willing to spend two or three times what makes any economic sense in todays market, given my expectations for the economy over the next few decades.

The rest of this trailer is built a little better than most. For example, the roof deck is 5/16" OSB over pre-fab trusses. If I can avoid the water damage, rot and mold that usually kills trailers, I should be able to keep this thing useful and in decent shape for the 30 odd years I’ll need it, before I downsize to a coffin. And if I can lower my heating bills to a minimum (I’m also spending good money on Huper Optik window films) then I should be in good shape for where I expect the economy to be (1970’s inflation revisited, with gas pump lines.)

If I remain with asphalt, I’ll probably have to replace the roof three or four times, shortly after each future hail storm. The current “home depot special” asphalt shingles probably won’t last 10 or 15 years even if no hail comes calling. And there is just no way to get a long lasting solar reflecting “cool” roof with asphalt. They get dirty.

8

I think I have a plan.

Two roof mounted fans, one at each end, one blowing in and the other blowing out. Turn this long skinny “attic” in to a miniature wind tunnel. Trying to move air in the more usual direction, from eave to ridge, in an attic that is 76 ft long by a foot or so high by about 10 feet wide (tapering down into the fiberglass insulation) is silly. Blow it the long way, end to end. Exactly two roof penetrations should be doable, on any kind of roof.

I really can’t even put in gable fans, as most of them want more than a foot of open “attic” height to blow into. I’ve only got 10" or 12" of vertical open space in the “attic” at the ridge. The fans need to be roof mounted. But that’s ok – there is a nice variety of roof mounted power vents to consider.

Would you suggest powered fans connected to the house wiring, or solar powered fans? Even the weakest solar fans have plenty of CFM for my needs. I’ve only got perhaps 1000 cubic feet of air in the entire dang attic. So a pair of such fans would exchange that air about once per minute. Enough to fly an airplane!

9

It sounds like your building is built better than most that I have seen.

I have no idea were Denton, TX is but perhaps you are in Ranchhand roofing’s service area.

10

[quote=“-Axiom-”]It sounds like your building is built better than most that I have seen.

I have no idea were Denton, TX is but perhaps you are in Ranchhand roofing’s service area.[/quote]

Denton is just north of Dallas - Fort Worth.

Is Ranch Hand Roofing in Dripping Springs, Texas? If so, that’s just outside Austin, about 300 miles south. That’s further than I imagine most roofers would want to go for a 12 square job, but I really have no clue of such matters.

11

I think that Mark of Ranch Hand Roofing is right near that area. I recall the name of Denton being mentioned one time before.

Ed