# Differences in a dryer roof vent for flat or sloped roof, if any?



## rickharp

This question is specific to a dryer roof vent. 

What is the difference in a roof vent for flat roofs versus a sloped roof? What makes one different, if there is any difference? 

How far the collar penetrates the flange? 
How large the flange is?
How high the opening is off the deck?
I am figuring, if the flat roof has tapered to a roof drain, and there are not parapet walls, then water buildup more than an inch would be unlikely. If the roof drains got clogged by leafs, and the scuppers were 6 inches up the parapet wall, then the vent would fail. 
The roof vent I am thinking about has a 3 inch collar that penetrates the flange and is siliconed at the penetration. The "house" incorporates the damper and protects the collared area. In this case, water would have to rise 3" or more to become a risk. 
The 3" though makes it hard to access for duct cleaners, so we are thinking an inch and a quarter would work (see bleow). 

Heavy snowfall regions may require the gooseneck opening be off the deck more than say 5 or 6 inches. 

Would love to hear anyone’s comments, discussions, ideas, what flaws exist with current vents, what aspects are good. and thoughts about this vent below. 

Thanks


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## Pie in the Sky

not sure how you would flash that on a flat roof. You could probably rig it up on some kind of curb.

D


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## rickharp

why would this vent need a curb. 

Are there pictures of roof jacks that are preferred for flat roofs that you could provide a link to. 

I guess because the drain slot is so low, it may get bulled or contaminated.


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## shazapple

Roofs are either hydrostatic (waterproof and able to hold water) or hydrokinetic (layered to shed water)

On our flat roof designs we design the projections to have a waterproofing height of 8", recommended 12" in order to deal with snow load, blowing rain, etc. The flange on that vent would have to have a built in lip and the whole thing be mounted on a curb in order to be feasible. You could probably bond the membrane directly to the top of the flange, but that would reduce the effectiveness of your drainage opening.

Another thing to consider is that a lot of flat roofs have problems with ponding (water that doesn't make it to the drain due to depressions or lack of slope, but will evaporate over a 48 hours period) or slow drainage which would cause water to back up slightly (inverted roofs for examples, or roofs with control flow drains).


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## 1985gt

Most dryer vents I've seen vent through the wall. I personally would avoid this vent at all costs. Or run a normal pipe through the roof, roof jack and strip it in.

I have seen vent's similar to these on houses for the exhaust fan for the range. I do not like them one bit as there is always a chance of snow or backed up water entering it.


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## rickharp

Thanks folks for your input and ideas. 
My direction with this is to add to the selling points of this vent that it works on flat roofs, but it is clear to me now that I ‘d have to add some disclaimers or recommendations. Here is my first draft. 

Recommendations for flat roof installs (conditions)…

- Not recommended for heavy snowfall regions without >8” curb
- Not recommended for hydrostatic roof systems (waterproof and able to hold water) unless a 6” or higher curb is incorporated. 
- Not recommended if any ponding greater than 1” is possible. 
- Minimum recommended slope is 1:.250” with positive drainage confirmed


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## Pie in the Sky

that should not be used on flat roofs Period. If it was, it would need to be Modified... Personally I wouldnt use it on a sloped roof unless it was over like 12:12


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## rickharp

Pie in the Sky said:


> that should not be used on flat roofs Period. If it was, it would need to be Modified... Personally I wouldnt use it on a sloped roof unless it was over like 12:12


 
Pie, I appreciate the comment, but this style vent is popular in the south. Could you or would you have time to reply with some technical comments regarding why it would not be your preferred vent for slopes between 2 and 12? 

Remember, the collar does penetrate the flange, and then is silicone sealed at the penetration. any water getting around the damper is drained away. 

Snow issues? 

Thanks again.


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## blageurt

Up here we call that a snorkel vent ......and it is flashed similar to a Plumbing flange / Chimney ........ I have installed many on both flats and Pitched roofs...not a problem if you know flashing detail.....


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## Pie in the Sky

Sure I will comment- 

Because your new you should know I am not a contractor I am more of a Consultant. But I have been involved in all aspects of roofing for my whole life. 
For low sloped roofing products meaning any membrane that requires flashing (basically anything below 4:12) there is no way to flash this unit. It is designed to be shingled into a system to basically flash itself. you can’t do that with any low sloped membranes. If you wanted to, here would be your options: 
· You could prime it and glue to it but that is not what it intent was. It’s a short term detail 
· you could build a curb maybe 2" smaller and bend down the flange to fit over a properly flashed curb. This is too much work, might as well buy something else.
· you could set it in a bed of mastic and screw it down. 
To me none of these are options. 
For roofs 4;12 to 12;12 I also would not use it because the exhaust is so low. It may work just fine down south where you have no Ice damming but its usefulness is its flaw. Has a short stack exposed to the weather minimizing condensation which drips back into the house. To me, you are asking for problems. Someone installs this in the wrong area and you have a big problem. Down south you have driving rain right? Won’t likely be an issue but it may. If the house becomes negatively pressured (happens all the time with wind) then it will suck moisture in. I understand these are extreme conditions but a typical roofer who is buying this doesn’t know or care about future repercussions. Hail can also cause something like this to leak by slowing down drainage.

I’m not saying this product doesn’t have some use but I feel like it really appeals to a very small market sector because a properly vented Dryer goes out a wall. Sometimes you can’t go out a wall and meet code, I get that, but simply buying a flashing piece may not be the only consideration. I guess I mean there may be other issues. Say they run it through an un-insulated attic? Well now all your moisture comes out while the pipe is vertical, where does all the water drain to?

I tend to be hard on new products – ask anyone in here…  and feel free to disagree, I’m used to it.


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## Pie in the Sky

For flat roofing I'd use something like this: :laughing:


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## shazapple

Or you could do this.


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