Another question: If the answer is fiberglass wrap, about how much linear pipe length will a 100 ft roll cover? About a 1/3?

First of all, if the DWV(drain,waste & vent) piping is installed correctly there should be an adequate pitch to insure there is never any standing water in the pipes so freezing is basically a non-issue. The exceptions to this would be P-traps which may be below the sub floor such as under the bathtub, shower stall or laundry standpipe. In this case the P-traps will generally be well up in the joist bay and very near the underside of the sub floor. General purpose insulation can be installed in the stud bay on the underside of the trap but do not insulate the top of the trap. Keep the top area open so that residual heat from the living space above can come through the sub floor and maintain a minimal temperature in the joist bay in the proximity of the P-trap.

Water supply lines are a whole different problem. We must keep in mind that insulation does not generate heat, it only retards the rate of heat loss. Even well insulated supply pipes will freeze if exposed to sub freezing to sub-zero temperature for a prolonged period of time. One method of protecting the pipe is to run it as high as possible through the joist bays and insulate the underside in the same manner as suggested for P-traps.

Another method is to run the hot & cold lines very close together, then install a circulation loop on the hot water line and cover both the hot & cold lines in a common insulation. In this manner the slight amount of heat radiating from the hot water line would be retained in the common insulation and thereby protect the adjacent cold water line.

The next option would be to install thermostatic controlled electric heating tapes on the pipes, then cover that with insulation to keep the heat in.

In regards to what type of insulation. It really doesn't make a lot of difference. While the preformed poly-foam insulation is what the homeowner is usually most familiar with, they make both poly-foam and rigid preformed sections of fiberglass pipe insulation with either a paper or plastic covering in sizes ranging from 1/2" diameter up to 20" diameter and they also make matching preformed covers for Tee's and elbows but you would have to get those types of insulation from a local HVAC or Plumbing Supply.

Do what lazypup said to insulate the pipes. I used the poly foam. Next thing you need to do is insulate the crawlspace.
The last house we owned for 20 years had a crawlspace and was located in NW Ohio where the winters are a little more severe than where you are at.

You will need to insulate the crawlspace. Isulation between the floor joists. If the pipes run down the middle of the floor joists put a 6" blanket of insulation underneath them after you put on the pipe insulation. That keeps the pipes from sweating. Where they go up through the floor into the house on outside walls, insulate as much as you can with the batt insulation. Tie it up around the pipes with wire if you have to. The outside walls by the pipes insulate with blue insulation board. Then in the winter close off all the vents with the blue insulation board. Keeping the outside air from getting into the crawlspace in the winter will go a long way to keep your pipes from freezing. My old house the ground temperature kept the crawlspace from dropping below 40 degrees in the winter. usually stayed around 50 degrees.

For this job (with access from outside via a single hopper window), I informed the customer of the following:

1) the crawlspace is not ventilated. Very musty.

2) the pipes are not insulated.

3) And the floor (3' above) is not insulated at all.

4) main drains and branches are not backfilled (maybe that doesn't matter, I don't know)

So, they probably haven't had freezing due to all the wasted heat through the floor and into this closed, musty space.

They have been notified, and so I suppose I will just wrap their supplies and traps as they wish. I think I'll forget about the batts in this case, since they have none to begin with.

Thanks very much for the input.