Galvanized pipe vent, replacing rest of stack


Old 06-03-19, 04:24 PM
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Galvanized pipe vent, replacing rest of stack

We've got a mess of galvanized/cast iron plumbing on one side of the house, for laundry (in the basement) and kitchen (1st floor). It's a huge mess, some runs uphill, and we are looking to replace most of it. We are redoing all the galvanized supply lines with PEX instead, and want to replace all or most of the galvanized/cast iron drain lines, since the drains run slow. We've cut out a section of pipe (to add a cleanout) and they are half-full of buildup. This stack is 2 1/2 inch galvanized, with a couple small portions of cast iron toward the bottom.

Is it okay to leave the top 5' or so galvanized, where it runs to the roof? This is above where a 2" vent line connects to the stack. So this is just the vent portion of the stack, and I imagine it isn't as corroded as the rest of the pipe. I worry about weight considerations, will the weight of the galvanized pipe put too much strain on the pvc? I just don't want to mess with the roof. We also plan on leaving the bottom portion galvanized, where it sticks out of the floor.
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Old 06-04-19, 04:21 AM
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Yes, you should be OK leaving the galvanized up at the top of the vent. Just make sure it is well braced and supported before you cut out the stuff below. You don't want it falling down or moving and causing a leak where it goes through the roof.

I don't understand what you mean by "...the bottom portion...". Any drain or vent lines that see waste or water really should be replaced. The horizontal runs especially as they love to rust out along the bottom.
Old 06-04-19, 08:01 PM
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Bottom portion

thank you! Yes, what I mean is that a 2 1/2 inch galvanized pipe is sticking up out of the cement floor in the basement (edited to add: that’s what the stack is sitting on—we are replacing everything but this bottom-most vertical pipe that is cemented in). I would love to know what’s going on under there and whether it needs replacing, but it’s not enough or a priority to bust up the cement or hire a professional.

The main (4”) stack is in the other side of the house. There’s a full basement bathroom which is also just plumbed into the cement far away from either of these stacks. I don’t know if or how or with what material these pipes are connected to each other. The main stack is cast iron, house is a 50s brick Chicagoland bungalow. Anyone know what’s typical?
Old 06-07-19, 10:41 AM
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Though I agree with Pilot Dane about supporting the galvanized as it goes through the roof, I'd consider replacing it with PVC if you're replacing everything else. Cutting it will be vibrating the roof boot, and if it's already old, may loosen any old hard tar that was used. It might be worth just running a new PVC vent and let a roofer (or you) re-boot and re-seal it correctly so you don't have to worry about it for a long time.

The underground piping you can inspect with a camera snake. Underground CI can easily last 100+ years, or can start degrading long before that. Depends on a whole lot of factors... and there's really no way to know without actually seeing it.
You can either leave it until it becomes an issue, or spend a few hundred $$ of a camera inspection and see what you're dealing with.

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