Best insulation for rodent resistance
pmartens
| Posted in Green Building Techniques on
We have renovated the ground floor of our house using a double wall flash and batt system with 4” of rigid foam and 6” of fiberglass, it’s overkill for zone 5a but that’s related to my other post this am. We made a point of putting a layer of pest block great stuff at the bottom of each stud bay before the spray foam contractor arrived but despite that, after 2 years we have rodents in the walls.
Does flash and batt inherently make rodents occupation easier? Is there a better method of super insulating that is not as rodent friendly?
thanks in advance
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About the only pest resistant insulation is aircrete and cement bonded wood fiber products. Pests will hapilly make a nest in the rest. Any of the pest resistant foam products are just marketing fluff, they don't work. There is nothing about flash and bat that makes it rodent friendly. Rodents will happily live in walls insulated with any batt or foam insulation.
The best way to deal with critters is a solid critter barrier. This is the same idea as an air barrier. It should be continuous across any cross section of the house and have no holes in it.
This is best done during build, since you are sided and insulated already, your only option is to find the holes on the outside of the house and seal them up.
+1 on Akos suggestion to get rid of the holes and cracks that provide rodent access. And generally this has to be solid, not just foaming the holes. Steel wool can be packed into some openings. For larger openings, I've used "hardware cloth" (with about 1/4" spacing between wires), rolled and/or crumpled up and forced into holes, and then using canned spray foam to help with the air sealing. Even red squirrels slow down when they try chewing on hardware cloth.
This is the final word in mouse traps. I mount mine on a 3" x 5" x 3/4" block of wood. Keep armed with fresh peanut butter and have them set in multiple places, especially the attached garage. Much cheaper than cats.
https://www.intruderinc.com/products/the-better-mousetrap
+1 for a hardware cloth barrier. You want this down around the sill, which is where most critters will enter. Other areas are where roof lines intersect, squirrels/racoons will try to get in there if they have a way to get on the roof.
I'm skeptical of the pest blocking abilities of great stuff pest block too. The only thing I've found that works as an air seal that rodents DON'T chew on is "duct seal", which is a type of tar-like clay. Duct seal is commonly used around wire and pipe penetrations. I've never found a critter to chew through that stuff. You can't really use duct seal to line an entire wall though.
My guess is that acoustical sealant would also act as a critter deterrent, since they don't like tarry and glue-like substances. There are downsides to using this material too though.
Bill
I've had a raccoon trying to climb up my downspouts before. He almost succeeded. Not sure what motivated him, but those critters can be pretty resourceful.
A mouse or two periodically makes it in. Despite lots of looking, I've never managed to figure out where or how.
I have a few wireless security cameras set up on some void spaces that mice seem to like when they do manage to find their way in. Even if they avoid the trap, I catch them on camera, and then know to double down with fresh bait and more traps. Even the most paranoid mouse seems to be susceptible to at least one type of bait, trap, or location.
Another trick in the arsenal is a mix of caulk and steel wool.
...stainless steel wool...otherwise it will just rust out and disappear.
Dr. Joe Lstiburek, building science evangelist, likes to talk about the four layers of a perfect wall -- rain barrier, air barrier, vapor barrier and thermal barrier. I would add a fifth one -- critter barrier.
One of the things Dr. Joe likes to say is that each barrier layer has to be continuous -- if you take a plan of the building, you should be able to draw each layer without taking your pencil off of the page. The same with the critter layer. And depending on your environment it needs to be able to keep out everything from bacteria to fellow hominids, and everything in between. Termite shields and window screens are part of the critter barrier layer, but in most places it's mostly about rodents.
That's a round-about way of saying I think you're asking the wrong question. The problem isn't that insulation is rodent-friendly, it's that your wall is missing a critter barrier. Just like with the other barrier layers, you have to figure out where your perimeter is and then make it continuous. Can insulation serve as both thermal barrier and critter barrier, the way that sometimes insulation can also be air barrier, vapor barrier or even rain barrier? I would say in general, no.
I have found the Great Stuff pest block to have a limited usefulness. Mice seem happiest when they have a nest site where the opening is exactly large enough for them to get in, that way nothing larger than them can get in and eat their kids. If they find a small opening they will gnaw on the edges to enlarge it to just their size. I have a theory -- unsupported by science -- that one of the things that draws them to a crack to gnaw on and widen is feeling a draft, which means there is a space behind the crack. I have found that sealing small cracks with spray foam will keep them from making exploratory holes. It doesn't work with active infestations, if they know there is a passageway they'll chew through the foam like it's nothing.
Foam reinforced with hardware cloth, steel wool or metal insect netting is very effective. But you have to establish a perimeter, if you just block one spot they'll find another.
"I have a theory -- unsupported by science -- that one of the things that draws them to a crack to gnaw on and widen is feeling a draft, which means there is a space behind the crack."
I don't have any citations to peer-reviewed publications, but that is exactly what I learned in pest-control classes. Rodent's whiskers are very sensitive to airflow, for exactly that reason. If they pass an opening with no airflow, they will often ignore it because it probably doesn't go anywhere useful. If, OTOH, there is a draft, they know it goes somewhere and they explore. This is why caulk and foam will often be entirely successful in stopping rodent entry. Agressive air sealing in our 100 year old house brought it from a rodent playground to zero activity, with no need for steel wool, hardware, cloth, etc. That said, the above comments are correct concerning active infestations, especially if there is active nesting. Rodents will chew through just about anything to get to their children. Eradicate the active infestation, then do the airsealing. When necessary, I've found that hardware cloth filled with spray foam stops just about anything.
My guess is they can also SMELL stuff in that air. Critter noses are notoriously good and finding food after all...
I agree about hardware cloth embedded in spray foam (including canned foam). I've used this myself many times. 1/2" mesh is a bit easier to get fully embedded, 1/4" mesh is a bit more critter proof. Either one is MUCH better than insulation alone.
Bill
Peter,
That's been my experience too. Rodent are pragmatists. They aren't going to just walk up to something and try and gnaw a hole in it with no evidence there might be a reward for doing so.
I have found they do have good memories too. If you block an entrance they know leads somewhere profitable, they will work to create another way in. It can take some time to dissuade them from trying.
There's stainless-steel termite mesh which "may" keep rodents at bay. Copper mesh will work as well. The purpose is to keep them from gaining entry into your walls rather than making the walls inhospitable.
Hello, one thing I try to do is pour boric acid generously in areas where vermin attempt to invade. This will slay insects as it messes up their exoskeleton and makes them dry out and kills them out right if they clean it off their feet. But it also does affect rodents. It doesn’t outright kill them but it diminishes their reproductive rate. The best thing is to seal a house up to the point where rodents and insect pests cannot invade. However, in the real world this doesn’t always happen. Be sure you do not leave boric acid in places that children or pets can find it. I generally leave some powdered boric acid on the top of the sill plate between studs after course spraying a mixture of 50% antifreeze, 23% borax and the remainder boric acid. Bring solution to slow boil to drive. off H2O. Antifreeze concentrate is still water loving so store solution in sealed plastic container. Don’t worry, this solution also kills and retards mold. It also retards wood rot. Paint on or course spray with safety glasses on. No mist spraying! Then apply pure Boric acid powder to surfaces to coat the wet solution. There are some people that claim that this also has the added advantage of less thermal expansion and contraction of the wood however this seems a bit suspect to me unless the Wood was just saturated with it first. Before anybody in this forum jumps all over me for using a poisonous substance like antifreeze in a wall assembly please consider that this is war! I just don’t like bugs and rodents living in my walls. They too are unhealthy and can cause serious medical problems. Boric acid in small amounts is used in some internally taken medicines. Again as others have more eloquently said it, the best thing of course is to seal up your house and not let any vermin get in. This isn’t always a perfect world however. I have had good success doing this. If mice can’t reproduce well, then that is an advantage. You have an edge on controlling them with traps. I hope this helps.
While I haven't completely looked into the chemistry of this, I'd advise against boiling these things in your home. Some people are VERY sensitive to the vapors that may be released, and you can have severe medical reactions if you're one of those people. Mixing up your own custom pesticides isn't usually a good idea unless you have a background in chemistry and know exactly what you're doing.
Be very careful here.
Bill
You are correct it is always better to well ventilate when heating everything especially with combustion products like a gas stove that I use to do this. I failed to mention I do my boiling in a very well exhaust vented spot. I took chemistry in college but truth be known we are all chemists and need to follow safety guidelines. If you cook food, then you are a chemist too. As we tighten houses up, air quality is of paramount importance for health. People go to great lengths and cost to eat healthy food, and drink clean water but often breath noxious fumes without even realizing they go directly into the blood stream. Perhaps this point would more appropriately be made in a air quality thread but consider how many liters of water do you put into your body daily and then consider how many liters of air you breath. If making your own solution doesn’t agree with you then I suggest you can buy the commercially prepared Boric acid antifungal sprays people use for wood during house construction for mold management or boric acid powders people purchase for cockroach control. I am not sure but I think they use propylene glycol instead of Etheline glycol or ethylene glycerol in the mold product as the carrier. I do not find this superior as it does not penetrate the wood and draw the boric acid in as well. Etheline glycol is a bit more water loving than Etheline glycerol so I prefer the latter but both work pretty darn well in my backyard testing. Perhaps I am just saving money but it really isn’t much trouble to safely make a bunch of this stuff. I use an old propane burner that was for deep frying turkey. Your comment however is well received and I appreciate anyone that is committed to safety and perhaps I should of specified what I thought wa obvious. We often get complacent when dealing with many products in this world and fail to read the label before bombarding ourselves with chemicals. BTW, Borax is a naturally occurring substance. My neighbor was dead against using it until he learned this fact. Now he thinks it is okay. Go figure. Just because something occurs naturally doesn’t mean it is good for us so we have to use it wisely to be safe. Before I developed this solution, I tried using a capstacin (the active ingredient in hot Chile peppers) solution. My backyard testing with game cameras showed deer were way more sensitive to this than mice! When rodents make up their mind to chew something they just do it! I have never found the perfect magic bullet on my war with field mice. I live in rural Montana and we have our fair share of them that would prefer to come into a cozy house each autumn. Not on my watch. We had one person die from Hantavirus in our county and it was determined it was caused by mice. They are welcome in my hay meadow but not in my walls.
There are many good suggestions above. The words that jumped out to me in your original post are "double wall" and "fiberglass." I've found this to be a particularly challenging combination. Rodents love to tunnel and nest in fiberglass, and double wall construction means that once they access the wall at any point, they can move freely without being blocked by studs. For this reason, rodent-proofing a fiberglass/double wall assembly needs to be done with an extraordinary level of detail. I've also noticed in my work a strong correlation between food sources and rodent population levels. The biggest issue in my area seems to be seed- and nut-bearing trees, spruces, walnuts and hickories in particular.
Another anecdotal data point for critters enjoying burrowing into fiberglass. Here's an infrared shot from an attic in NH that I examined... those 'warm dots' appeared to be spots where mice or similar critters made holes and nests in the insulation. In case it's not clear from the image, the insulation is loose-blown fiberglass.
Yikes! The war rages on. I found it helpful when I learned from this thread that duct mastic may help repel rodents. I bought some immediately from Amazon and will implement back yard testing as soon as some of our snow melts so I can actually see what the mice are doing with it.
Bats like warm attics too and are as difficult as mice to keep out. They burrow in under the blown insulation near the drywall to stay warm. I have a customer who has had a bat problem and they had to be careful when opening the attic scuttle. The scuttle was in the house and when opened the bats would sometimes fly into the living space. I spent some time sealing all of the bat sized openings I could find that lead to the attic, flashings and soffits meeting roof are an easy point of entry. Have not heard any more from them so I believe the extra sealing of holes worked.
That is a good point to remember. Airborne division of varmits! The war rages on.
So from the majority of replies it seems that a double stuff wall with fiberglass is pretty vulnerable. How is dense pack cellulose? If I remember correctly cellulose is usually treated with boric acid to reduce flammability, does that also help with its appeal to critters?
As far as mechanical breaks, that’s tough on an old house with multiple additions. We have tried to tighten things up at the joint between foundation wall and lumber but it’s tricky. We have been parging the rubble fill wall so maybe we should start using a section of wire lath under the top of the parging tucked in behind the vinyl siding at that juncture?
You are correct it is always better to well ventilate when heating everything especially with combustion products like a gas camp stove that I use to do this. I failed to mention I do my boiling in a very well exhaust vented spot. I took chemistry in college but truth be known we are all chemists and need to follow safety guidelines. If you cook food, then you are a chemist too. As we tighten houses up air quality is of paramount importance for health. People go to great lengths and cost to eat healthy food, and drink clean water but often breath noxious fumes without even realizing they go directly into the blood stream. Perhaps this point would more appropriately be made in a air quality thread but how many liters of water do you put into your body daily and then consider how many liters of air you breath. If making your own solution doesn’t agree with you then I suggest you can buy the commercially prepared Boric acid antifungal sprays people use for wood during house construction for mold management or boric acid powders people purchase for cockroach control. I am not sure but I think they use propylene glycol instead of Etheline glycol or ethylene glycerol. I do not find this superior as it does not penetrate the wood and draw the boric acid in as well. Etheline glycol is a bit more water loving than Etheline glycerol so I prefer the latter but both work pretty darn well in my backyard testing. Perhaps I am just saving money but it really isn’t much trouble to safely make a bunch of this stuff. I use an old propane burner that was for deep frying turkey. Your comment however is well received and I appreciate anyone that is committed to safety. We often get complacent when dealing with many products in this world and fail to read the label before bombarding ourselves with chemicals. BTW, Borax is a naturally occurring substance. My neighbor was dead against using it until he learned this. Now he thinks it is okay. Go figure. Just because something occurs naturally doesn’t mean it is good for us so we have to use it wisely to be safe. Before I developed this solution, I tried using a capstacin (the active ingredient in hot Chile peppers) solution. My backyard testing with game cameras showed deer were way more sensitive to this than mice! When rodents make up their mind to chew something they just do it! I have never found the perfect magic bullet on my war with field mice. I live in rural Montana and we have our fair share of them that would prefer to come into a cozy house each autumn. Not on my watch. We had one person die from Haunta virus
When I was looking into using all-borate cellulose, I questioned the several installers I got quotes from about its rodent-deterring abilities and each of answered that although it might be less attractive to mice than other types, they still witnessed rodents using it for nesting. I live in a rural setting with lots of mice- this past summer yielded a population explosion and I was catching no less than 6 per day. Not a one in my house, but they run right up the side of the house, along the underside of the overhang, and up the tin roof channels to some tiny entrypoint to my attic where they've ruined the fiberglass with their urine and feces.
In my new house 100' away, while framing I discovered droppings on the ridgebeam. No cooking odors there of any kind. Aside from wrapping the entire sheathing with hardware cloth I don't believe anything besides eternal vigilance and a lot of traps will help if you live in a rural setting. I'm actually installing 3' of tin siding from a concrete shelf off the slab up to the first course of siding in the hopes of slowing down their access. The damage they do is unbelievable. I discovered that they had chewed two tunnels into closed cell foam, each over a foot long.
I've had a pretty good track record with double walls and dense-pack cellulose; I've done a couple dozen homes using this approach over the last 15 years and have had no reports of problems. For some reason, rodents don't seem to infest dense-pack as badly. I suspect that the borate irritates their membranes, and the tunnels tend to collapse in on themselves. A few years back, we had a project that was a double wall initially insulated with denim batts. It was absolutely destroyed by mice. The homeowners gutted the area (only one room fortunately) and we retrofitted with netted dense-pack, which seems to have solved the problem.
Like I said before...sadly there is no magic bullet in the realm of insulation to stop rodents. Mice like all the types of insulation for the same reasons green builders do. Any way you can prevent entry in the first place is your best spent money. The vermin solution I suggested only helps a bit and traps are you last line of defense. Cats don’t work all that well as it drives mice back into the walls for additional destruction to your house. I heard that having a ferret works so I got two of them. The odor of those critters had me willing to go out into the hay meadow and encroach on the mice! I gave them away.
You could potentially add hardware cloth in vertical sections between inner and outer studs in a double stud wall at periodic intervals to break up the wall into seperate "rodent compartments". This would greatly limit the ability of rodents to tunnel horizontally along the wall, and would keep them contained to only the section of the wall they managed to enter.
I think it would generally be better to just do a good job of detailing the bottom and top edges in a rodent proof manner though to keep them out of the wall in the first place. Hardware cloth is cheap, and it can be installed at construction time with a stable gun and some tin snips. Not a big deal. I do recommend using stainless steel mesh along the bottom of the wall though as I've found the leaf debris tends to cause the galvanized mesh to rust in a relatively short period of time, and aluminum mesh tends to rot away in a year or less.
Bill
Bill, I was hoping to install galvanized mesh and bug screen at bottom and top of rain screen. Do you think that would dry out enough to last a long time? I only have pine trees where I live.
If you don't have a lot of tree debris and splashed water then you're probably fine. In my area, we have a lot of wet oak leaf debris and that stuff seems to be pretty corrosive at least as far as rotting out metal things is concerned. Stainless steel is impervious.
The downside is that if you go with galvanized materail and find you have a problem down the road, it's very hard to replace. If you go with stainless steel, you spend more money up front but you're pretty much safe forever. That's the tradeoff.
BTW, it's not so much about the galvanized material "drying off", it's what it's getting wet with in the first place. One way you could maybe do a test is to see if you have any existing galvanized things around near the ground that you could check and see if they show any signs of corrosion. If they look OK, then you're probably safe with galvanized material. I like using stainless because I don't want to worry about future failure and I'm OK spending a little extra for insurance, basically.
Bill
I think you have a excellent (as do the mice) Designed wall. You are not the first person to fall to the claims of anti rodent foam products. Mice just don’t follow the rules nor can they read the label. I admire the honesty of the cellulose applicator. I wish someone far smarter than me could conjure up a bombproof anti vermin design short of the additional full house antivermin continuous layer mentioned earlier. Joe Lstiburek, I hope your reading this. Ha ha, I’m hoping that having the fiber cement cladding and metal bug screen as well as additional wire cloth at the top and especially the bottom of my rain screen will do the trick. Probably not. Those little mice are tricky. They seem to outsmart me from time to time. One even tried to bum rush past me when I opened the front door. He didn’t know I had another exterior door on the other side of my mud room to block cold blasts of air when the front door was opened. It didn’t take long for that mouse to become a casualty in the war.
Use gooey stuff to seal any sneaky paths. I've found that mice do not like to chew duct seal, which is a tar-like clay substance commonly used to seal around pipe and wire penetrations in masonry walls. Acoustical sealant will work on smaller gaps (it's messy though, so be careful with it). I've found that mice don't like things that stick to them, so such products are good deterents where you can't put in a real barrier.
Bill