I'm planning on updating the plumbing in my 1943 house. Some was done before I bought the house. There is pvc pipe installed under the house connecting the waste drains to the city system. However, the pvc ends just below the subfloor in the crawlspace, and I can see rusty iron going up into the house, presumably the original pipe. Should all the iron be replaced with pvc?

My house inspector found a significant drop in water pressure when more than one faucet was turned on in the house. What causes this and what's the fix? I have copper and iron pipes in the system.
Thanks!

If your supply lines are iron; scale will reduce the volume and result in less water when more faucets are turned on. I would recommend updating these to copper or PEX. Cast iron drains appear to hold up very well. I have read articles where cast iron drains are still functional hundreds of years later.

Cast iron pipe can look bad sometimes but be just fine... I always say that you only fix it if it broke... I mean, if you are updating/remodeling the bathroom and/or kitchen then I say you replace all pipes to new ones for sure! If it is leaking anywhere... replace for sure, too! BUT just to replace cast iron pipe... not a common practice where I come from unless there is pitting (small leaks) or as said we begin a remodel.. then , of course, get rid of it then... PVC pipe so easy to put in... depends on level of updating, etc.

The drop in water pressure is probably a volume issue... here, the pipes have probably been piped 1/2" to everything and there is probably sediment build up in places (especially transitions from copper to iron pipes). I would definitely recommend replacing all this to copper or cpvc or pex pipe... depends on your plumber's recommendation and where you are in the country.

Anyway, there is my opinion.. *wink*. Hey, if this answer was helpful, please RATE THIS ANSWER by clicking on the button below. Thank you!