Anything that I’ve seen done, or have tried myself, only made the nesting places that much safer and warmer.

I recommend getting an estimate to have the job done by a contractor. That’s one phase of house construction that I’ve found I save very few dollars doing it myself. You can also pick the estimator’s brain while they’re there.

Recommend ALL damaged insulation be removed. The full depth of the joist should be the insulation depth. Use hardware cloth to hold it up, quarter inch by quarter inch welded galvanized, this will keep all rodents out .

If I were you, I would replace what insulation I was going to, then from stud to stud, roll out some chicken wire or aluminum screen (depending on the size of the pest) and staple it to the bottom of the wood, it will help keep the insulation in place but keep out the pest.

First off, I’m with @Tropical_Willie about replacing it all. The old stuff is toast.

I found that just some heavy-duty plastic and a stapler worked. (We had barn board floors so we didn’t have to worry about humidity buildup or anything like that.) A double-layer of that sheeting was enough of a barrier to wind whipping under our house that it was noticeably warmer with the plastic than it was with just replacement insulation alone. Pretty handy in a NH winter, and something you can’t get from “hardware cloth” a.k.a. chicken wire. It seemed to keep the field mice out just fine, and had added benefits.

A couple of things I have done in the past.

Chicken wire over the entire underside. Advantage, it is easy to install, relatively cheap and keeps the majority of the batts from falling down. Downside, rodents can still get through and chew up the insulation but at least not in big chunks.

Rigid insulation board stapled or nailed (if you nail it, use the plastic buttoned felt paper nails) on the bottom of the floor joists holding in the existing batt insulation. More expensive but does add insulative value. Downside is rodents can still eat through it and it provides them with a semisolid surface to nest on covered by the batt insulation they chew down and line their nests with. Upside, you can’t see that they have done this.

Thank you all very much for the helpful ideas! Great Answers!

When I looked at the picture, my first reaction was the same as @Tropical_Willie. Remove old insulation and fill joist area to the edge of the joists with new batts and cover with hardware cloth. Your overall “R” factor will increase, and there will be enough insulation that if the critters get past the hardware cloth they won’t take enough to make a noticeable difference.

@jerv There is a difference between hardware cloth and chicken wire.

@Yetanotheruser The link to hardware cloth you gave lists chicken wire as one use, and most chicken coops I’ve see use the square stuff rather than the hex stuff, so I consider them interchangable.

@gondwanalon I would use suitably dense enough wire and the little fellow you have as your avatar. Between the mess and his/her hunting skills, i would sleep peacefully.

@jerv When I cleaned chimneys I used hardware cloth on many occasions for pest barriers. I would not be confident using chicken wire, thus my distinction.

@Yetanotheruser Ah, that explains it. Personally, when I’ve needed something with more structure than chicken-wire, I’ve gone right for the expanded metal, which is unquestionably different.

Expanded metal is so much overkill. All you need is something that holds the insulation in place.

I like the idea of using small mesh wire screen that will keep the rodents out and the insulation in place. Perhaps it’s overkill but it would discourage rodent activity. I think that that justifies the added expense. Let the rodents go find another place for their nests. HA!

@rojo Yes, it is. Expanded metal is better used for things that really need to be strong, like machine guards.