Anybody have one of these vents on their roof?

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Anybody have one of these vents on their roof?

Postby Tukanu » Sat Nov 02, 2019 9:20 am

My roof is curved, so adding a conventional vent will require some modification. I was wondering if anyone is using this smaller vent? I think it could be installed on a curved roof.
How have you handled the round top roof problem?
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Last edited by Tukanu on Sat Nov 02, 2019 10:34 am, edited 1 time in total.
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Re: Anybody have one of these vents on their roof?

Postby tony.latham » Sat Nov 02, 2019 9:33 am

How have you handled the round top rood problem?


When you say round, just how much curve do you have? (I see how much curve you have on your build log.) But let's get objective vs. subjective.

Image

Set a 14" piece of wood where you want the vent fan and measure how much gap is exposed on the ends. I'll bet it's less than 1/8".

:thinking:

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Re: Anybody have one of these vents on their roof?

Postby Tukanu » Sat Nov 02, 2019 10:37 am

I think it was more like 3/8 with a 14" piece of wood...maybe a 1/4". I read somewhere that a guy tried to install by adding a bunch of goop....sounds like a bad idea.
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Re: Anybody have one of these vents on their roof?

Postby tony.latham » Sat Nov 02, 2019 11:27 am

I think it was more like 3/8 with a 14" piece of wood...maybe a 1/4".


That is a lot.

One of the reasons I built our second teardrop was that our first –-a Hunter commercial 'drop-- didn't have a roof-vent fan. It had a computer fan in the bulkhead. It moved the air from the cabin into the galley which had two side vents. It was noisy and didn't move enough air. That's how important ventilation in a teardrop is.

It's (almost) rare for us to run the fan where we camp. But we always have the vent at least cracked. When it's warm, it's all the way open and it does a great job pulling air in from the windows while our body heat convects out the top. When it's hot, that's when we run the fan for a half hour or so to get the cabin cooled off in the evening.

If it were me, I'd explore fabricating a couple of wedges to form a 14" flat spot. Nearly 200 square inches moves a lot of hot air.

:frightened:

Tony

p.s. Gorgeous build you have going. :thumbsup:
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Re: Anybody have one of these vents on their roof?

Postby eLink » Sat Nov 02, 2019 11:46 am

I'm wondering if it would really be so bad to simply "squash" the roof skin flat just around the opening to a typical 14" square MaxFan.
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Re: Anybody have one of these vents on their roof?

Postby working on it » Sat Nov 02, 2019 12:44 pm

* If you've already purchased, or have your preference set for a "Fantastic Fan" or such, overhead, then Tony's idea of making wedges to follow the curved roofline makes sense. But, if you want an alternative, then consider using computer case fans mounted on side-vents, and a more powerful table-fan/air circulator mounted elsewhere to boost airflow when needed. I addressed this in an earlier post (actually in several posts):

working on it wrote:
  • I circulate plenty of fresh air, without a roof vent, and without the possibility of leaks or damage to the vent, and with a lower roofline, by mounting sturdy steel vents on the sidewalls. The combination of the steel , waterproof vents (with computer case fans helping airflow) and a strong main fan inside the cabin, provide as much air circulation one mght need, in any weather conditions. The awning-style windows help out, too, when open, even in the rain.
  • I built my TTT for strength, durability, and weather resistance, with no exterior feature vulnerable to the elements. Especially on the roof. I've been in trailers that had roof leaks: from either the overhead A/C unit, a torn rubber roof, or (most frequently) from a roof vent; that ruined the interior. I just recently had to replace the damaged/deteriorated plastic cover on my 20ft trailer's vent (which had cracked, and was leaking), before I stayed in it, while my new house project was underway. It was replaced before any water damage had occurred (soaked up by the wool vent insulator, and didn't get past it), fortunately, but it reinforced my view that overhead vents were prone to damage & leaks, over time.
  • I wanted waterproof vents, preferably not installed in a vulnerable spot (less chance for damage? tree limbs, hail, meteorites?), like the roof, and made of steel, not plastic.. Having run a shipping/receiving dock for years, I saw enclosed trailers with all types of venting, and wanted to emulate that in my build (also an automotive-type piece, which I was leaning towards as a sub-motif). I narrowed the choice down to two "enclosed trailer vents", normally roof-mounted, but would serve even better mounted on the sides. Here's a comparison of the two "finalists" I chose between: http://www.etrailer.com/comparison.aspx?pc=RV-626-062&pc2=9139 Primary usages are to admit insect-free ambient air, and expel humid stale air. Computer case fans are mounted behind them, to make them more efficient, at a low power cost. The vents were to be sealable, waterproof, screened, and rust-resistant. I chose the Redline 9139 (also partly because it looks like a drive-in speaker!- liked the retro look), and it has a butterfly closure for tunability.
  • In hot weather, the interior is cooled by A/C, in moderate weather by a 11" fan (and two awning-style windows), and in cold weather, by one or two 200 watt heaters. Small computer case fans circulate minimal airflow thru the upper wall vents at all times, reducing humidity build-up inside. A high-flow fan (a Honeywell 11", under the front overhead shelf) uses variable fan speeds and angles to circulate the interior air.http://www.tnttt.com/viewtopic.php?f=42&t=69753


* Overkill air circulation, I'm sure, but very versatile. Possibly more versatile than if I had a single "Fantastic Fan" overhead. I usually only use:
  • 1) A/C during hot weather (+ central fan if extremely hot),
  • 2) the central fan (only), with side windows (awning-style) opened during warm-ish weather, even if raining,
  • 3) side vents (always slightly open, for CO2/humidity control) and case fans used ( cool weather, no heater running), and
  • 4) central fan, case fans, and 1-2 Lasko 200 watt heaters (on cold nights...cold for Texas, that is).
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you can never have t6oo much air circulation (in Texas heat).JPG
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sidewall vents & computer fans on swing-out hinges.JPG
sidewall vents & computer fans on swing-out hinges.JPG (155.71 KiB) Viewed 2036 times
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Re: Anybody have one of these vents on their roof?

Postby Tomterrific » Sat Nov 02, 2019 2:31 pm

Make a perfect fitting "box" to mount the vent.

Get a 2 x 4 and a pencil. Hold the 2 x 4 on the roof where you want the vent. Use the pencil raised on a small piece of wood to scribe the curve on the 2 x 4. Cut the curve. Scribe the curve on another 2 x 4. Cut that. Use the ends of the 2 x 4 to get the angle for the front and back pieces. Mount the box with plenty of PL to seal it. You can use window flashing tape to make a flashing for extra waterproofing. Mount the vent on top as normal.

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Re: Anybody have one of these vents on their roof?

Postby Tukanu » Sat Nov 02, 2019 3:40 pm

What is PL ?
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Re: Anybody have one of these vents on their roof?

Postby John61CT » Sat Nov 02, 2019 4:18 pm

Loctite PL Heavy Duty Sealant

Butyl rubber can be built up, then cut the excess and use a sealant like that around it.

But a low-profile inset box would be easier to prettify
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Re: Anybody have one of these vents on their roof?

Postby campbellinaz » Sat Nov 02, 2019 4:42 pm

eLink wrote:I'm wondering if it would really be so bad to simply "squash" the roof skin flat just around the opening to a typical 14" square MaxFan.
RoofVent.JPG


What you’ll want to do is build a “curb” that is up off the roof enough to create a flat space for the roof vent. You definitely do not want to force the roof into a different shape as your just asking for problems.


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Re: Anybody have one of these vents on their roof?

Postby pchast » Sat Nov 02, 2019 9:03 pm

When you force the roof flat installing a fan base
you make low spots to puddle water in a storm.
I'm fairly certain it will encourage leaks. :thumbdown:
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Re: Anybody have one of these vents on their roof?

Postby eLink » Sat Nov 02, 2019 11:15 pm

Good points. I think a raised curb would work well with a monolithic waterproof skin, like fiberglass.
But if you're skinning with aluminum (like I am), maybe ripping the spars with a slight camber up would get rid of any low spots and provide positive drainage all around the vent opening?
RoofVent2.JPG
exaggerated camber for clarity
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