Roof Vents

I did an inspection on a home approx 8 years old with the original roof covering. I noticed that there were repairs to replace missing shingles in one small part of the hip roof. It was approx 12 shingles. I also noted thatmost of the vents appeared to be improperly installed. I wanted to throw this out there for suggestions on how you might report this in the inspection report.

Vent apron improper.JPG

The vent in the photo is a “Broan” damper exhaust vent for a bathroom exhoust fan, and not an attic exhaust vent. At least it should not be, if it is.

With the exception of the shingle being cut and butted just ever so slightly, too tightly to the portion of the vent gooseneck which is above the roofline, it looks to be installed correctly. In the interior of the attic, is there a flexible ducting tube connected from the bathroom exhaust fan and tightly connected to the snap on ring on the interior bottom side of the damper vent?

If you are not familiar with this type of vent go to a Menards or Home depot and look at one out of the box so you can see what I mean.


Thanks. I was not sure on that one. I will check it out. What about these in this photo?

Improperly installed vent aprons.JPG

If you are referring to the 3 large objects consecutively positioned along the rupper area of the roof, they are an enlarged static air exhaust vent. The NFVA would have to be referenced via the product manufacturer.

I am having a brain cramp, and although I have never installed these large ventilation vents, I do know that one of the companies who manufactured them, was taken over by GAF Roofing Corporation. So, the GAF website may provide similar NFVA for those like products.

Or, you can generalize an assumptive output.

Determine the entire length of the vent hole. Lets just say, since I can not measure them that the vent hole cut out is 3 feet wide by 1 foot vertical height, giving 3 square feet total. Then, reduce that total amount in half due to the air inhibitting sceening most likely contained within. Therefor, if these dimensions were true, each vent product would provide about 1 1/2 square feet of NFVA exhaust ventilation, or 144 x 1.5 = 216 square inches of exhaust ventilation. This would be comparable to 4 of the standard static air mushroom, (or turtle) style roof top vents, which provide about 50-51 square inches of exhaust each.


P.S. Note how the 2 damper vents we discussed earlier are just beneath each of the 2 plumbing vent pipes. That is a give away that they are over the 2 bathroom areas.

Why are most of the home’s I see have the vent aprons below the shingle? As a generalist inspector should I even comment on these installations? My question is, is the bottom of the vent flashing supposed to be over top of the shingles? Why are there so many other applications where the vent flashing is below the shingles, not above. Which is preferred?

Shingle style means that the next course of shingles, and even sheet metal flashing aprons, should be installed on top of the previous course or row.

When the shingle is laying on top of the bottom apron, water flowing down-hill has an opportunity to travel under the top edge of that individual shingle.

The specifications show it to be laid as I described and the other way is incorrect.


Thanks. Why are so many installed the other way? I have referred to the specs you suggested and understand the way they are supposed to be but most are not installed correctly then. Or is it that they installed shingles over the bottom portion of the apron that marke it appear to be underneath when it is not?

Firstly, many roofers do not know proper specifications.

Secondly, as a guess, they may do it in the improper fasion in the misguided notion of providing a more cosmetic looking job by coverung up the exposed portion of the bottom apron flashing or they believe, that since the other 3 sides are covered, the bottom one should be as well.

Thirdly, most roofers do not know or follow the proper specifications.


Thanks for your help. I appreciate your opinion and am sure this post has helped others.

I’ve never seen shingles installed at this odd angle, and it looks to me like water running straight down the roof will run beneath the tab of the shingle just downhill from it. Is this right?

It looks like the shingles covering the bottom part of the vent flashing are a completely different color than the roof. I’m wondering if they were not installed by a homeowner who was “improving” his house by covering up that “ugly” flashing. Otherwise, who did it, and why?


Airvent is one manufacturer:

Scroll down to the middle of the page.


Installation instructions are here:


Unless I missed an additional illustration or link from Air Vent that you supplied, the ones referenced on that page are just the standard sized 50 sq in slant back louvre vents.

The ones in the attached photo from OP, ar significantly wider than those. I have seen them, but rarely.

I am extremely familiar with Air Vent and the “Ask The Expert” seminars, and have even provided Paul Scelsi some alternative application methods for expanding the usage with only a slight modification to their existing Shingle VenII design, where it could be used as a parapet wall vent, as opposed to leak prone aluminum strip bents commonly used in the real world.

BTW, If any of you have never attended the FREE Air Vent seminars, go to their web site and get their nex seasons schedule. You will all find them educational and enlightening.


The different colored area of shingles you are noticing eminates from just under each of the 2 lead plumbing vent pipe soil stack flashings. That is a chenical electrolysis (sp) reaction to downward flowing rain water picking up or having a reaction with the lead boot flashings. The result is that the immediate downward area gets “cleaned” off from any “algae” or microbial growth in that area continuously and will stand out from the rest of the roof. That just goes to illustrate how intense the microbial discolorization is on the remainder of this and all roofs.

Next time you are driving down a treet with some steeply pitched older roofs, look directkly below the sheet metal chimney flashings on the shingles below and any other metallic object on the roof. The cleansing action occurs from any metallic object, although the products sold specifically for this purpose are generally composed of either zinc or copper.


In the first picture, there is no metal of any kind above the shingle that is past the side of the vent. Why the discoloration on that one? I do see the discoloration under the stack vent in the second picture. You’ve seen the condition first-hand, and I have not, so your explanation must be based on what you saw, Thanks.

What is the damper exhaust vent made of?


Rain blows sideways at times also.


…and cleans off exactly one shingle, never affecting the adjacent ones, and blows equally at a 90-dgeree angle? Riiiight.