Where we operate that means using a non combustable barrier (such as dense mineral wool) in the floor cavities with 1 (or 2) layers of 5/8 fire rated (Fire-X) drywall on the underside ceiling.

I stalk up when on sale plus my plumber buddy gives me used but nice ones he's pulled for his higher society customers when they upgrade just because.Sometimes it takes me 12 minutes to change a faucet if the fasten rings are really corroded to the underside of the countertop. 22 minutes if the stop valve is bad and I have to install a new 1/4 turn. 

I am glad I did, the underside was already getting cancerous. 

Without sealing the entire underside of the house the rodents had access to the entire crawl and could make their way into the garage.  

I bought it at auction a year ago and now have my second tenant family living in it.The driveway is about 25 feet from a 4 acre woods (neighbor's property) and the tenants have problems with rodents eating their car wires and the insulation attached to the underside of the hood on both their vehicles.

Most women look at them & shudder.Gas stoves also collect mouse haven spillage on the tough to get to underside of the 'sealed' burners.

One small example were rats chewed a hole in the underside of the roof and got into the attic.

We re-create drawer fronts all the time our new houses we buy that are missing them and also if renters break them and very often we have to lay in another piece of Louan over the rotted underside of the sink.

@Jaron Smith, It almost looks like barnacles on the underside of a whale, yikes!

You want to dig next to it and dig deep enough until you get to the underside of the footing.