# Flat/Low-Slope Ventitation



## Dan (Feb 13, 2014)

Hi All in new. I'm a flat/low-slope roofer. 

Last year I ran into several flat and low slope roofs with vents on the top of them in different scenarios (2/12 slope, barrels, and near dead level). One of my goals this year is to learn about ventilation for my customers so we can make good recommendations for them. 

We've replaced some whirlybirds for customers with damage ones so I called lomanco and they said they could not really make recommendations for flat and low slope roofs other than they needed curbs (and I've never seen one in the field with a curb only without). 

Does anyone know where I should start looking for information on this topic?


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## 1985gt (Dec 21, 2010)

http://roofvents.com/roof-vent.html

The curb ones are the best, although you can strip them in.


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## shazapple (Dec 3, 2010)

We usually use something along these lines
http://www.ventilation-maximum.com/English/product-model101.html


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## wfduggan (Feb 14, 2014)

Are we talking about venting the roof system or venting the interior space.


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## Roofer Louisville Guy89 (Feb 15, 2014)

*Vents*



1985gt said:


> http://roofvents.com/roof-vent.html
> 
> The curb ones are the best, although you can strip them in.



I like the curb ones the best as well. I work for Louisville Roofing in Louisville KY. RoofingQuoteLouisvilleKY.com


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## Dan (Feb 13, 2014)

wfduggan said:


> Are we talking about venting the roof system or venting the interior space.


Venting interior space. Thanks for the links guys, I'll look into those manufacturers and see if they have any resources for me. 

What I really want to learn and be knowledgeable about is their purpose and when they are needed in a flat roof and when it might be a good idea to remove current vents or add some.


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## RoofPro (Oct 29, 2008)

*slope not a big factor*

Dan:

I’m sure you are aware venting can be a bit complicated. In my opinion the industry standards used to determine when venting is need, and how much is needed have little to no scientific backing. All that being said, if there is space between the (thermal, air and vapor) barriers and the under side of the roof deck slope has little effect on the amount of venting required. 

Under winter conditions the level of venting is primarily a mater of how much heat and conditioned air is escaping the living space into the attic. If you have really good air seal, and high R value in the assembly theoretically you won’t need any venting. On the other hand if you have poor insulation and lots of air leaks (from things like pull down attic doors, can lights, chimney chases,….) you could need a lot more than the industry standard (1/150 or 1/300). 

Another factor that drives the need for ventilation is heating / cooling equipment and ducts located in the attic. If this is the case you may be better off moving the thermal barrier to the roof – that is adding insulation under the roof membrane. 

In most cases you’ll be doing your client a huge favor by adding a blower door test and air sealing to the work scope. The extra money they spend will likely be recovered in reduced heating cost in the first year. You may want to check your local branch of BPCA (Building Performance Contractors Association.)


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## Dan (Feb 13, 2014)

Thanks RoofPro, I looked into the BPCA a little bit and it seems to be more targeted toward residential building but the issues are probably no all that different from residential to commercial. 

That got me looking at some building envelope sites do you think this might be the kind of training I'm looking for: http://www.besinstitute.com/certified-building-envelope-courses.php ? 

Or might you recommend something else? I'm sure up to looking at self study kinds of things too.


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## RoofPro (Oct 29, 2008)

*Besi*

Wow
I like to think I have a fairly good pulse on the roofing and building envelope industry. Bit embarrassed to say I’m not familiar with BESI. Looking at the web site and the course descriptions they seem similar to BPCA, I don’t see much on Air Barriers or Air Leakage Testing, but maybe I just missed it. I would not mind attending one of their programs

Another organization worth checking out is RCI 
http://www.rci-online.org/international-convention-ce.html

Regarding your situation – in my opinion the number 1 factor in attic ventilation is Air Sealing between the attic and the living space. If the building envelope is leaky good ventilation may just suck more conditioned air into the attic. The number 2 factor is proper balance in the ventilation system – the air intake must be the same or slightly greater that the exhaust. 

For self study my favorite source on the subject of ventilation is a guy by the name of Joe Lstiburek. He does a number of training events for BPCA, BPI and the like. If you get a chance attend one of his presentations, very informative and his approach is entertaining. You can find several of Joe’s ventilation and air sealing articles in a google search. 

http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation


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## LCG (May 30, 2011)

Most flat roof manufacturers make some sort of roof vent that has a hot air weld able or epdm flap that can be use din conjunction with their system.

http://www.ibroof.com/sites/default/files/tds_5in_8in_alum.pdf

http://www.ibroof.com/sites/default/files/tds_8in_metal.pdf

Other manufacturers make something similar. We have used these with no issue. One of our local markets has attic spaces under all of their flat roof decks. These buildings usually have a series of 24" China hats on them that we retrofit with a new pipe boot but if they don't we generally use the manufacturer's vent.

It's amazing. These old buildings have 2-3' attic spaces, no insulation, skip decking, ZERO insulation, and a coal pitch roof. Not a drop of mold anywhere to be found.


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## Dan (Feb 13, 2014)

Thanks LCG, glad to hear we are not the only ones running into these. I actually ran into a low slope (1/12 maybe) roof recently with a ridge vent on a curb down the center. 

Similar to yours no insulation on the deck just EPDM and then the "attic space" is has quite a bit of insulation in it. And it was working well, no moisture found in the attic. 

But I would like to have a strong base of knowledge to recommend leaving it the way it is or putting in something similar to those vents you gave links for.


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