I thought this would be quickly resolved by simple googling, but all I got was pages of people posting the same question to internet forums and getting wisecrack replies. So I thought I’d add some value to the Internets and post the question here on these forums, to see what kind of replies I get.
I am getting ready to install a new ceiling and some recessed lights in the attached garage, and plan to use Romex to daisy-chain the lights together. Dear, sweet mother in law warns me that I must use metal-clad cable, because rats will get into the ceiling space and make short work of any exposed wiring.
I don’t see how there is any way on Earth that a rat (or anything for that matter) is going to chew its way from the outside in unless it has titanium teeth. As long as utility holes are properly sealed (and not with something wimpy like spackle, but with mortar or concrete), this ceiling space should be rat-proof.
The last thing I want is an “I told you so” from MIL, so if any construction-oriented folks would like to talk me down, please feel free to do so.
The likely entry spot was the garage door. Most people open it occasionally and they will scoot inside, and then begin making there way through any interior openings or even gnaw through drywall or wood in the ceiling. They can also squeeze through remarkably small openings where the door meets up against some interior surface to close. I had garage doors where they gnawed through the bottom corners. I attached steel plates to the doors at the bottom, then replaced the meager wood molding that the door seated against with PT 2x4s. And use the metal clad for the wiring because they can still get in through an open door.
I think I wasn’t clear in the OP. There are presently no rats in the garage. The gnawing damage I’ve found is in the ceiling space over the living areas (hall ways, bedrooms). There is a thick concrete wall between the main part of the house and the garage. I guess what I’m asking is: given the construction of the room (solid concrete on all six sides), is there any conceivable way a rat could get up into the ceiling space? The only way I see it happening is by gnawing through a 4 inch thick concrete wall.
And by the way, I’ll be using cement board for the suspended ceiling. Not sheetrock. And no wood framing or molding is involved either (the termites here are ravenous). All window & door framing is aluminum.
But how do they get from the floor up into the ceiling? Little grappling hooks? Maybe I’m underestimating them. Can they really scurry up smooth concrete walls and then hang there for hours while gnawing their way through a cement board ceiling? There is no sheetrock in the picture so there’s nothing to dig claws into.
Off-topic, but I confess I’m curious how it is that you’ve turned your garage into such a fortress while your living space is infested. Is the garage meant to be sort of a panic room, in case the rats overrun your home? ;)
I’ve seen mice climb concrete walls that looked impossible to get a grip on. Not sure if a rat could do it. But if there’s enough texture to get their little claws stuck in they will do remarkable things. And they definitely chew through wiring insulation if they can reach it. Doing the ceiling in cement board will keep them out of there from the interior. Steel mesh fabric over any exterior wood should stop them from getting in that way.
Not sure the OP has a mole rat problem, but the graphics are impressive.
We have native wood rats (aka pack rats), a bit smaller than imported city rats. They do not chew through metal. Hardware cloth, steel pipe, steel wool stuffed into small cracks, metal cladding, will defeat them. Wood and sheetrock will not. Mice and rats can go up walls in quite an unbelievable way. They can also pass through holes of unbelievably small diameter.
The impressive graphics available happen to include a mole rat but any rat could chew through concrete in the same way given enough time and incentive. Their teeth grow back as they wear down so they can slowly work their way through almost anything one tiny nibble at a time. “Do not” and “can not” are not the same expressions - as noted it is a question of incentive versus time and energy. AFAIK they can not chew through steel, but they do frequently chew through other lesser metals, pipes, wire mesh, etc.
The whole house is poured concrete. They build them that way here and in other (perhaps most) parts of southeast Asia due to potential flooding issues and the nasty termite population. You may recall the floods that hit parts of Thailand last winter; this house was meter-deep in filthy canal water for a month. Luckily, there was no real damage since it’s all tile and concrete. But it was a bitch to clean once the water finally drained.
The rest of the house would be just as impenetrable if various utility workers and other numbskulls had properly sealed-up holes made for running air conditioning pipes, electrical feeds and such. But they just left huge gaping holes everywhere. I personally stepped on a rat in the kitchen a few weeks ago whilst in the kitchen for a 4 a.m. drink of water. I believe this rat came in every night through the range hood exhaust pipe, which has no screen, wire mesh or anything to prevent pests from freely passing through.
Since the garage is fairly small and unadulterated by utility access or plumbing, it has had no such problem and remains pest-proof.