Leaking Shower Drain - burst pipe? corroded?

I *just* purchased my first house and last night our first disaster struck. I live in Michigan, in a 2 story house with a basement. The Master Bed and Master 3/4 bath sort of overhang the first floor by about 3 feet - the master shower sits above this overhang.
I was taking a shower last night and my boyfriend was outside in the yard. When I got out of the shower he was yelling about water coming out of the house. Indeed, there was a copious amount of water pouring from the overhang directly beneath where the shower is located. There is no indication of water inside the house at all. The shower is all one piece fiberglass installation.

The house sat vacant since September, and I'm sure they didn't fully winterize the house as the water and power were on when we purchased it - we did however, have a very bad storm which left much of the city without power (thus without heat) for 5-7 days. And I'm wondering - could the trap have frozen and burst?

Its either that or the drain has corroded or broken somehow.

I'm hoping that its the winter thing, which means that water has only been going down and out the wall for 3 days and not 3 years... A plumber could easily cut into the overhang to inspect the drain as well, so I'm not worried about needing to pull up the entire floor. But water is a destroyer... I'm envisioning tens of thousands of dollars to repair this problem and I just bought the house and have no money for something like that. Any ideas? Any idea how much something like this would cost?

Until you open things up, there's no easy way to tell. Overhangs are notorious for poor insulation, and water in the trap with no heat could very well have cracked the trap. Even with great insulation, no heat for 5-7 days below freezing could do it. As to what else may have gotten wet, again, no way to tell until you open up the area underneath. Once you get that fixed, you'll want to put new, dry insulation back.

The plumbing fix could be quick and easy, the carpentry may end up more, and will be if you pay the plumber to do that as well. Best for you to probably open it up so it is exposed.

As Jim stated, no easy way to tell what happen or how extensive the damage is until you open things up. Remember, insulation does not warm anything. It slows heat transfer, but won't stop it. It would be a fairly safe guess that the trap was not winterized and broke, but guessing doesn't fix anything. Do as much of the tear out as possible yourself, no point paying a plumber for "grunt" work you could do yourself. Water will ruin insulation and drywall, and can cause wooden floors to warp, but won't do much to the structure itself. Get the wall and floor opened up, then you can start dealing with contractors.

Also you will want to put heat tape around the p-trap and drain pipe i have lived in a house that whenever we had a cold snap the water in the p-trap would freeze solid as a rock no where near as cold as your home and it was just a small ( tub width ) overhang in S.L.C. Utah
you can set the tape to a switch in the bathroom so you only have it on in the cold weather

I pulled out the metal strainer on top of the drain and it's a PVC pipe, There aren't any obvious cracks but I couldn't see far enough into the trap either. The good thing is that our other shower is not connected to the issue as there was no leaking when we used it, so we're not in a big emergency mess.

There's no indication of water damage on any of the surrounding floors or walls - and besides the point at which the water was dripping off the siding, there's no indication of ANYTHING outside the house either.

That gives me hope that it hasn't been going on long enough for serious damage to have occured. 3 showers in 3 days after sitting empty for 9 months is all that's happened.

All the more reason to open it up so it can dry out while you figure out what needs to be done to fix it. The longer things sit wet, the bigger the problem.

I pulled the soffit down, cut through and pulled out insulation under the flooring and found the drain pipe. I have found that the problem is not a busted trap, but that the seal between the fiberglass insert and the drain assembly itself is no longer water tight. If you push up against the drain, it opens a noticable gap under the inner drain lip, which appears to be screwed into the lower drain part.

It doesn't have any cross bars or anything to unscrew it and I think it may be glued in place.

Anyway, a plumber is coming tomorrow, but is this something they'll charge $250 to fix when I could just as easily fix it with some plumbers putty and caulk for $20?

A big problem with fiberglass shower pans is that they aren't very strong. So, if it flexes any at all when standing in there, this has little chance of long-term success. Nearly all of this type of pan really benefits, and will last MUCH longer, if you set them in a bed of mortar or similar setting material so that the bottom is fully supported. Then, they can't flex.

Dependign on the type of seal, it probably relies on a rubber gasket, wedged in place. If it is loose, it probably got there because the pan can move/flex. Without fixing that, no repair will last, and no, plumber's putty and caulk won't last.

Can't even guess what a plumber will charge, but I will tell you that you can't fix broken pipes with stick'em. From your description, I'd say there will have to be a certain amount of disassembly, cleaning, and firming up before proper repairs can be done. Cost depends on time, materials, and local plumbing charges.

Yes, you can fix the drain by removing the old one, and reinstalling a new drain. I prefer Silicone in that situation.

If you call someone over to do the work for you, then yes, of course he has to charge for parts and labor.
Would you go over to his home and give his van a tune-up for $20?

Putty can dry out over time. I find myself repairing those all the time now.