Low-slope roof vent

hi. I’m trying to vent a 1:12 roof that has not been vented.
The top of the roof meets the wall of the house, and the 2 sides also meet walls. So it is essentially boxed in on 3 sides. About 12’ x 18’.

My idea is to install adequate soffit ventilation, and one solar-powered exhaust fan in the middle near the top if this roof. Below, I’ll drill 1" holes in the the top of each of the rafters to connect the bays for airflow to the fan.

Is this a good idea?

this is on the northwest coast so there is a lot of rain and a lot of wind as it faces the weather What is the best way to flash fan? should it be curbed?
oh, the roof is torch-down.

my desire is t do a good job, am nervous because it seems like there are a lot of ways to do it incorrectly.
thanks.

Why would you vent a low slope roof anyway. Its torch down i have never seen a vent for the attic in one of those roofs. Ever.

As much as I dislike them, this may be an application for a turbine vent.

Whatever you use make sure it is raised above the roof deck, ie no ridgevent or wall vents unless you build a curb for it.
I think a better solution is insulation.

[quote]
My idea is to install adequate soffit ventilation, and one solar-powered exhaust fan in the middle near the top if this roof. Below, I’ll drill 1" holes in the the top of each of the rafters to connect the bays for airflow to the fan.

Is this a good idea? [/quote]

You have the right idea but your slope is too low for the standard venting products.
You have a special case that requires a non-standard solution.

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My idea is to install adequate soffit ventilation, and one solar-powered exhaust fan in the middle near the top if this roof. Below, I’ll drill 1" holes in the the top of each of the rafters to connect the bays for airflow to the fan.

I don’t think the fan is going to provide enough suction to pull the air from all those bays through a series of 1" holes. If it had that much power it would be sucking your insulation out too. I would probably not worry too much about venting that deck. While venting is a good thing it’s not common practice on what you described.

They make vents(like a half ridge vent) for shed roof to wall terminations. Build a curb along the top wall and vent the whole thing. Find a good roofer. Preferrably one with a sheet metal shop.

They make vents(like a half ridge vent) for shed roof to wall terminations. Build a curb along the top wall and vent the whole thing. Find a good roofer. Preferrably one with a sheet metal shop.

I was actually thinking about running the bays in the roof so they open into the back wall and then vent the back wall 18"-24" up off the roof deck. Same suggestion minus the curb building… But then I thought about driving rain or heavy snow loads and thought better of it. Just too many ways for it to leak.
For it to work you’d need to design a vent that is open underneath where the air has to travel up through a baffle system or something. But now you have a passive eave/soffit and a passive curb/wall that is enclosed on 3 sides…not going to be much air flow going on and still a chance of leaks. Soffit vent is better than nothing but I would probably pass on trying to rig an exhaust vent there.

I have vented such roof by installing vented drip edge at the eaves. The roof we vented did not have an overhang as it sounds like yours does. With addition to a “roof to wall” vent. Also install baffles or at least make sure there is adequate space for the air to pass through.

My question is:

Why do you wish to vent this assembly?

In regards to the question of why i am trying to vent this.

This is not an attic space, it is living space beneath if that makes a difference. It was insulated with no air space and a half-hearted vapor barrier. I opened the ceiling up looking for the source of some water spots and in addition to some leaks that i have remedied above I found a good bit of moisture and mold on the rafters and sheathing. It seems that now would be the time to get air moving up there while I have it open.
The climate is essentially temperate rainforest and it seems like air flow would be the best thing to counter moisture, condensation, and mold.
One builder has suggested that I definitely need to vent, but this forum was my 1st second opinion.
Thanks everyone for the feedback.

gtp1003 you say that you have never seen a torch-on roof vented?you must not be a roofer,its code where I’m from(any low slope)

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gtp1003 you say that you have never seen a torch-on roof vented?you must not be a roofer,its code where I’m from(any low slope)

That is a pretty ignorant statment considering that building codes differ from city/state/region.

Your right code or not,it would be ignorant to not put vents in :idea:

Well john since im a steep slope kinda guy that would be a different ball game. Every flat roof i have seen did not have one in there. I just love it when newbies flex there brian power. And yes i have had many years in this trade. I just do not do flat work.

Let have a round of beers for the know it all in the back.

Your right code or not,it would be ignorant to not put vents in

Backing up one ignorant statement with another is not going to earn you any respect around here, lol.

I may be new to this forum,but the truth is the truth.I’m not a know it all and dont need your respect tar monkey.Im not new to the roofing industry at all,thats what I’ve done my whole life,so my input is just as important.Ignorance=not knowing something.I know what I’m talking about!! :stuck_out_tongue:

Sorry if I offended you gtp1003,that was not my intension :wink:

I believe it is the 2003 IRC nation wide code, that requires all roof assemblies to be ventilated. It does not get too specific about unusual circumstances and specialty applications though.

Although that being said, unless I was installing over a very large, or even moderately sized structure, this would not be done, as it is just one more penetration for a flat roof to eventually find a leak source.

Use alternative venting systems for unique applications. If there is an access to ventilate the soffits and to also ventilate with a full exhaust product, I would do that, but not in the middle of the roof assembly.

Ed

I may be new to this forum,

Yes, you are new here. Don’t expect to walk in and start insulting long time members and not get called out for it.

I’m not a know it all and dont need your respect tar monkey.

Good, this forum has plenty of know it alls already. Nobody needs anybody elses respect noober, what you need is your own effing email account instead of using your old ladys, lol.

Im not new to the roofing industry at all,thats what I’ve done my whole life,so my input is just as important.

Wow, a lifetime roofer…what an achievement. golf clap Truth is that your “input” as you call it is just like everyone elses and it’s called an opinion. You said, “The truth is the truth…” which is pure bull. There is no single “truth” to roofing, there are only opinions and as in life everything is relative.

Ignorance=not knowing something.

Thank you Mr. Dictionary, I see you know how to Google.

I know what I’m talking about!!

Did you stamp your foot when you wrote that? lol. Keep telling yourself that. If you say it over and over and click your heels together three times maybe you won’t be a roofer anymore.

Look, you come in here, insult a long time member and make ignorant statements. They are ignorant because building practices and codes vary ( as I’ve already said ) from region to region. What you do up in Canada is different from practices in Arizona or Scotland. The fact that you could say someone must not be a roofer because they have never seen a flat roof vented is flat out stupid because you are IGNORANT of key information like:
1 where that person lives and what climate
2 what facet of the business they operate in
3 what the norm is for roofing in their area
4 what the local building codes are
etc.

So yes, you made an ignorant statement, backed it up with an ignorant statement and then made a lame assed apology saying how it wasn’t your intention to offend which frankly makes you look like a complete bozo because that was clearly your intention.

You guys ever sell those two guinea pigs?

Yeah we did sell the guinea pigs,thanks.And not that its any of your business but I use her email because its the one checked the most.your the only one with the problem here,all I was trying to do was make a point about flat roofs being vented.And I am proud to be a roofer,its always been my bread and butter

Just my 2 cents. Ive seen millions of squares of flat roofing here in Michigan and the only ones that were ever vented were durolast roofs. And thats because they go over wet old roofs. There is vents on most roofs but they vent the interior not the the roof system.