Slant back vents letting in snow!

I got a call from a customer whos roof we replaced back in sep 2010,customer stated that there was wet spots in several rooms,first thing i thought was condensation from gas heat pipe,i have ran onto this many times,upon inspection of the ceiling,i noticed the wet spots were spaced apart pretty evenly,I checked the attic and was frightened at what i saw!!,There was atleast 3 gallon bucket worth of snow laying on top of the insulation below each vent! We did get 22 or more inches of wind driven snow,but still,the small air vents on the sides of these 750 vents are so small. It seems almost impossible for this much snow to enter through these holes,they are not the cheap 750s they are lomanco. I am wondering what to do to keep this from happening again???

Unbelievable :shock: Lomanco square vents? Do you have pic.I always seal vent flashing undernees,when install,but never seen ice or snow inside the vents.

this is the lomanco 750 series,a very popular vent around here KC MO it didnt leak around the vent but through the sides!,the pile of snow made it look like there wasnt even a vent over the open hole! WOW

We have found this to be very common with the slanted back Air Hawk vents - They draw or suck snow in…Negative Air pressure perhaps?? not sure, but we have definitely come across this same issue. WeatherPro vents have never had this problem in our experience. Trying changing out the vents - I’m sure that will solve the problem.

I’ve seen it once or twice with RV too. For some reason, they’re acting as intake, not exhaust. Chimneys has positive air flow. That’s why the fireplace doean’t fill with snow even though the top is wide open.

I did a barn years ago and it was lamanaco’s 750 nand yes it was letting in snow. if figured it was location of vent vs wind direction on the normal days. What i mean is some vents placed oposite side of the wind and back flow when there is just gable vents. all i could figure. i made shoots for them but thats all i could do. high snow area high wind area nothing much i could do.

The typical slant back roof vent will allow snow in through the side vents. The only vent that will truly block snow is the WeatherPro 50 roof vent which Duraflo makes.

did ya check soffits? have had the same issue and it was because the insulators (around here) seem to enjoy blocking all the soffits, when we clear them it stopped it…

It is rumored (or known?) that if a roof has more ventilation higher than lower meaning, more ventalation on the roof than in the soffits,than this problem could occur. Also Turbines style vents and 507 vents dont mix, the turbines could pull rain and snow through the 507s. Also if you have gable vents and not enough soffit ventilation and 507s this could occur.

That vent with all the holes in the side looks like a leak waiting to happen, and so it has. We use vents from Menzies, same guys that make all our fancy pre-bent flashings. They have the AF-50 and AF-90, with no air holes in the side.