I sealed up a home last fall for bats aND owner found one recently inside home. I have been out twice since then searching every where for some thing I missed or a repair that came loose and nothing. Only thing left is the powered attic fan. I have not seen them use this before but I think it's plausible. Any suggestions before I loose my mind. Thanks Jaco
b

Anything is possible if there's enough of a gap and the bats can get through without being turned into ground bat.

+1


On the inside, can you staple some 1/4" hardware cloth over the opening?

I've seen a number of them that the raccoons have pushed the screen in, catching the fan blades and blowing the motor. The only way

to prevent that is a large outside cover. They cost between 50 and over a hundred dollars depending on what you want.

Had bats access through square roof vents numerous times...many people have that switch in their home that they dont know what it goes to...usually an attic fan...since it aint on...it is likely a good possibility....pop the cover off of ot and look

yep here in the north east. also find them dead below the fan, blades must hit them. I have seen them hanging on the inside of the screen.

Have I ever seen a bat enter/exit from an attic fan, no. Do I believe a bat could enter/exit from an attic fan, yes. Do I think this would be a common entrance/exit point for bats, not at all.

If a bat(s) were using this my first guess is that they would be climbing under a loose shingle tab and accessing an opening in the roof that way. Now this type of activity I would consider common. If you look at the physiology of a bat versus the construction of an attic fan and combine that with how a bat enters structures, it would involve the bat either landing on the roof and then climbing the side of the fan to gain access (to get out they would have to fly up the tube, land on the side of the fan and then crawl out), or they would have to fly under the cap and land directly on the lip of the fan tube and climb down it to access the attic. To rule out the fan, first take off the cover and see if there is a screen in place or not. Second, do a bat watch if you're still not sure focusing on the fan. Of course, you can always just install a 1/2 x 1/2 cover over top to keep out raccoon and squirrels if nothing else.

The approach I take on conflicts like this is to look at what the weather was like before they found the bat. I still verify that I didn't miss something and that I didn't have a material/application failure or that there isn't a problem with the structure that wasn't there when the work was initially completed (I've had this happen multiple times with building shifting and materials pulling away). If storm fronts were moving through during the evening/night and you had daytime temps of 60+ I'd look at refuge points like chimneys, gas water heater exhausts, alcoves, etc. as possible entrance points. However, if the weather was nice without storms, then I'd say in most cases your clients did something that allowed the bat to enter like leaving a door/window cracked (it is spring cleaning time), leaving the garage door open until late at night, or even bringing the bat inside in a box or on a plant that is brought in for the night.

When I do recover a bat in a situation like this, I like to determine the species and sex as that will tell me more about what is going on than anything else. If it is a female big brown, I know most likely there is still an opening that the bats will be using. In those cases, you may have to do several bat watches to find it. If it is a male big brown bat and there were storms, I know it most likely is a bat that had taken shelter and ended up getting "trapped" in the living space (regular gas hot water heaters vented through chimneys are very common with this scenario). If it is a red bat or silver haired bat, I know it most likely is something the client did to allow the situation to occur.

As a side note, this is also why I only guarantee bat colonies from the completed structure, not individual bats. Trying to figure out how a single bat entered a structure is the most difficult aspect of bat work and in most cases it can never be solved as there are just too many variables.

X2.

But I have seen bats use the small square roof vents for access. There is a style that has a round "pipe" under the cover with a super-lightweight bug screen. The screens sort of lay on the top edge, maybe tacked in a couple places. I have seen bats exit these, and have found guano pellets under the vents (on shingles) and even find bats hanging on the INSIDE of the screens.

It's NOT common, but it does happen. I think Mike Paine (Iowa) has also seen this a few times.

I've seen them in the vents themselves roosting, as well as using them to access the attic. These were just roof vents though no fansin them just that very flimsy screen.

MikeD

Thanks all for the input. I have plans to seal this vent up this week and see what happens.

Seen bats at least once (long time infestation, high-pressure) sitting on the outside of the flimsy screen under the cap.

Seen bats at least once (long time infestation, high-pressure) sitting on the outside of the flimsy screen under the cap.

I went back to this property yesterday and performed an attic and basement inspection. I found 1 dead bat in the attic near the fan and 1 dead in the basement. What I think has happened, as this was a pretty good size colony and I'm sure they had a strong desire to return for winter, is that this attic fan was sort of one way trap and the few bats that entered it had difficulty exiting and perished inside the home. I am sealing the attic fan today and hope this fixes any future issues.

JBarnes,

Was the original bat they found in the attic or in the house living quarters? Just curious, I have folks that I show they need to repair or replace their window screens when performing inspections or exclusions and usually the following year the single bats are often associated with this lack of home maintenance. In some of these I had to really push the point of fixing these ripped screens and windows due to summertime and how the bats that are used to that old roost are right there in proximity to the window even if only night roosting, more prone to end up inside.

I'd agree with what everyone said, with fewer years and Ron, Eric, Dave an the others, every year I see some random thing that I never thought was a good place to enter or to roost, but there they are, why bats are not only so frustrating but so interesting in their behavior.

I have screened beneath these fans you referred to, just for the sake of knowing they wouldn't become an issue.

So many as was mentioned are tack welded in 3 or 4 places with flimsy screen.

Justin

I don't like to screen below the fans due to birds filling the fan area with nest.

Jim,

Good point about the birds, my area lacks a lot of the pressure from starlings and other birds that many have.

Sometimes these differences are very important when reading posts, don't want anyone thinking NM is the norm screen when the bird nesting issue is major in their area.

Good point!

Justin

Yeah, you can get squirrels nesting there too sometimes.

X2 Paul

Justin,

The original bat last year was found in the house, which spurred the phone call to me. They called in late May, so I opted to wait till fall for the eviction. I am almost 100% sure that when I excluded them in the fall, a few found this vent open and went into the attic for hibernation. The homeowners called me about 2 weeks ago saying they heard something in the wall crawling around, and 1 week later is when I found the two dead bats. I quoted them a price for the attic vent cover last year for squirrel/raccoon prevention, and they declined. From now on, I am only going to guarantee my work from now on if I get permission to seal these vents as well. I have wasted 3 trips on warranty fixing this issue, and these kinds of calls drive me batty!

Jacob