Yup, I am back with another question for my new van build!I got the biggest and fanciest Maxx fan, for a great price. But then someone questioned whether it would cause my roof to vibrate and thus leak.I took the ceiling off, and here is the roof structure. The orangey color is osb built into the fiberglass. The green is plain fiberglass. Tthe roof has two levels. There is a flat orange part(osb), then a sloped green part, and then another flat osb part. As you can see, the old fan is near the slope, so that adds some stiffness. The osb is formed around it, so it mounts only to the thin fg layer.If I put the new fan where the old one is, is that cool? Do I need to add metal or plywood ribs for stiffness? Should I put it somewhere else instead?Thanks much for any advice!

i would put the New fan, there where the old one ismost likely that area is already re-enforced with some one by two framing where the vent frame is screwed/fastened to the roof

I have put in a new vent with a fan as part of it for an "all in one" and I just can't see where vibration could cause a leak. The new fan will be "balanced" fairly well in itself, and the only place it can leak is up on the roof if not properly Dicored. The Dicor is flexible if there is a tiny vibration (which I doubt) and you have to keep adding more Dicor every year anyway as part of your regular maintenance. Some Eternabond is also good if it gets to be an "issue" in an older rig.You also have the advantage of using the old fan's electrical connections if you just replace it with the new one. The vent cover might have to change size if you are going to a heftier sort of vent fan, but that is not the question here.

Thanks, everone!There is no 1x2 or other framung, just the single layer of fiberglass. Does that matter? Should I add framing? And a 18" square of plywood?

The vent screws into the roof all around and you Dicor over that, so if the screws won't go in the wood as is but only into the fibreglass, then you need to add something like more wood inside the hole or else extend the vent edges to reach the wood that is there. Those Rv vents are a standard size so not clear what the old vent screwed into.There is also the inside part that screws up into the ceiling

Is it ok to put a Maxxair fan here? | Good Sam Community

30 Replies

pianotuna
Nomad III
Aug 06, 2017
Inside for the wood. I would use marine grade 3/4 inch. (i.e. water proof)
Naio
Explorer II
Aug 06, 2017
Thanks, BFL and Mex, it sounds like I do need to take steps to make it more rigid. The roof does not curve MUCH, so making a piece of wood to transition from curve to flat probably means a sander rather than a saw.

I guess I would use a plywood square the size of fan flange, cutout for fan and sanded to fit curve of roof. Stiffer than 1x2s. I have scraps of ext plywood in all thicknesses. I am guessing 3/8 or 1/2", as 3/4 would be heavy, unless I need it for the curve.

Is there a preference of inside vs outside for the wood?
Naio
Explorer II
Aug 06, 2017
Thanks for your concern, landy. It IS freshly painted on the exterior. Hitop guy used regular rustoleum. 2 coats at least, I think.

I, too, am surprised how much light comes through. But I like it! The green light is like being in a forest. I plan to leave it uncoated on the interior, at least through the first winter, so I can spot any leaks.

(The brown swirls are glue from the shag carpet that was up there. I will get as much of it off as I can.)
MEXICOWANDERER
Explorer
Aug 06, 2017
On Quicksilver, I had to have hatches built to conform to the curved roof. To simply slap those fans onto a flexible surface risks "drumming" caused not by fan motor or blade imbalance but airflow eddies amplified when a breeze is flowing across the fan inlet.

Simple reinforcement with pine spacers will help prevent drumming and leaks caused by flexing. I have used a product called NUTSERT backed with metal fender washers when access to the rear side was available. Google NUTSERT if you need the term defined.

But custom-fit pine seems to be the easiest way to get the job done with reinforcing.
landyacht318
Explorer
Aug 06, 2017
That much sunlight getting through the fiberglass means the gelcoat is gone. I'd get some paint on the exterior as sunlight's UV light will deteriorate the fiberglass and the polyester resin used to saturate it.

I use rustoleum topside yacht enamel at about 15$ a quart. It is many times better than their regular enamel, but Interlux yacht enamel is 25$ a quart and much better.

Get some butyl rope for under the flange of the fan. Do properly prep the roof surface before adhering then screwing fan down.

Degrease before painting, paint longevity is all about the prep work

https://www.amazon.com/Second-Skin-Damplifier-Butyl-Rope/dp/B0155KELRW
BFL13
Explorer II
Aug 06, 2017
The vent screws into the roof all around and you Dicor over that, so if the screws won't go in the wood as is but only into the fibreglass, then you need to add something like more wood inside the hole or else extend the vent edges to reach the wood that is there. Those Rv vents are a standard size so not clear what the old vent screwed into.

There is also the inside part that screws up into the ceiling
Naio
Explorer II
Aug 06, 2017
Thanks, everone!

There is no 1x2 or other framung, just the single layer of fiberglass. Does that matter? Should I add framing? And a 18" square of plywood?
pianotuna
Nomad III
Aug 06, 2017
Go for it!
BFL13
Explorer II
Aug 06, 2017
I have put in a new vent with a fan as part of it for an "all in one" and I just can't see where vibration could cause a leak.

The new fan will be "balanced" fairly well in itself, and the only place it can leak is up on the roof if not properly Dicored. The Dicor is flexible if there is a tiny vibration (which I doubt) and you have to keep adding more Dicor every year anyway as part of your regular maintenance. Some Eternabond is also good if it gets to be an "issue" in an older rig.

You also have the advantage of using the old fan's electrical connections if you just replace it with the new one.

The vent cover might have to change size if you are going to a heftier sort of vent fan, but that is not the question here.
MrWizard
Moderator
Aug 06, 2017
i would put the New fan, there where the old one is
most likely that area is already re-enforced with some one by two framing where the vent frame is screwed/fastened to the roof

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Is it ok to put a Maxxair fan here?

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