Cast Iron VS. ABS - replacement

[Boink]

I've got a quality home built in 1970 that has cast iron DWV (including all rain-drains). Most of the regular sink/laundry drains, which are easily accessible, are 2" cast iron (all held together with couplings that are easy to separate). I'm now finding some problems and am beginning to think that it would be just easier to swap out a significant main line (and 3 subs leading to it) with ABS and with regular clean-outs. Am I nuts? It wouldn't be a big job at all and I guess I'd be solving several issues at once. I'd leave the exisiting cast iron in the walls until those lines leave the floor into an area I can get to... and then I'd use some kind of Fernco coupling to switch to ABS. I'd have to eventually re-join a 4" cast iron sewer line (where there is a 2" to 4" Y).

Associated questions: 1) are there any issues with drain lines in unheated spaces that could freeze? 2) is a 2" line (existing size) adequate to collect a kitchen sink (with dishwasher), laundry sink and washing machine? Everything is vented OK.

Thanks

[Peanut9199]

The benefit from ABS to Cast Iron is that Cast Iron will build up like a clogged artery. The drain will get smaller and smaller but can be cleaned with a jet drain washer.
The pipes will not freeze and burst because with a drain as apposed to a pressure pipe it's not full of water.
A 2" line is fine for what you have.
You can use both at the same time if you want to slowly change over slowly.

[Gary Swart]

One thing that should be pointed out about ABS or PVC compared to cast iron. You will hear water running through the plastic pipes but not with cast iron. Of course, the plus side is ABS or PVC is easy for a DIYer to work with, and it's cheap by comparison. If you want to go plastic, ou need to decide if you want to use PVC or ABS now, you can't mix and match easily.

[Boink]

Thanks Peanut and Gary:
Yes, I was aware of the sound/noise issue but these pipes are in an area where it doesn't concern me at all (and I'll never really hear them). I was also aware of the ease of useing ABS (common here in Oregon), with cutting/fitting just plain simpler to measure and dry-fit... and I can use couplings (with the metal band) to clamp the new to the old. I also don't have heavy stacks to deal with.

The only reason I mentioned freezing is that I didn't know about sustained cold and the possibility of any, small amount of ice. Of course, I suppose that the cast iron is just a prone (and this isn't much of an issue where I'm at).

In examining the existing pipes, the occlusion isn't as bad as I thought, with some rust but my 3/8" snake zips through it with ease. But I've found a tell-tail wet spot on one pipe that probably means I've got a small crack in it (with minor seepage).

So, it looks like I'll be replacing this 25' total run (dropping 1/4" per foot) and with 3 feeders into it (and a new clean-out or two). All will be 2" so-as to couple to the existing 2" to 4" horizontal "Y" where my new stuff will end.

[Peanut9199]

Abs pipe and fittings should be in indoor and pvc outside but it will perform at an operational temperature range of -40°F to 180°F.

[Boink]

These pipes will be effectively in a large crawlspace (and with no sun on it).

[Peanut9199]

So as long as the temp doesn't go below -40 and there is no shock (someone hitting it) ABS is fine. If not you can run PVC DWV which can withstand more.

[Boink]

Well, by-golly, I've done it (with the help of a knowledgeable buddy). It turned out very nice. Added several clean-outs just for good measure (though I doubt this system will mis-behave, and I still have good access to all lines from the vents). Thanks for the advice.