Replaing plaster with drywall: lots of questions

Am getting a 1920’s home renovated. Location is Southern California. This is not a DIY post requesting help but one asking for advice on how to proceed and have contractors do the right work for the house’s specific case. Some questions:
Ceiling: It has plaster ceilings. Some of the plaster has broken off from what I assume was previous water damage. It seems rather than replaster, it would just be easier to hang drywall. A contractor said the loose and all existing plaster will be all removed but the lathe will stay and ½ drywall can be hanged. I asked why not ¼ given weight considerations and his response was the ceiling might look wavy with the thinner drywall. Also, the lathe can stay unless planning to put up insulation (as the house has none). Even if I do not want insulation installed, should the lathe be removed anyway? He said one reason was that it gives the ceiling more strength to let it stay in place. What do you think?


Thanks in advance!

 

The only reason I can see to leave the lath would be if the joists are uneven or not on 16" or 24" centers.
Why would you not want insulation??

 

The lathe should be removed primarily because you will never get 100% of the bits of plaster out from between the lathe. Also insist they remove it because otherwise they will screw the drywall to the lathe and may not necessarily hit the joists... which is asking for trouble.

 

Great points made by both of you. I am a layperson and didn't know at all. Any risks to installing drywall in place? Any reason to just have them replastered. I did do the replaster on and outdoor ceiling but it was expensive. Should drywall cost more or less? I'm guessing the demolition of the lathe and plaster will drive the cost up in either case?

 

Demolition will drive up the cost but it is something most diyers can do if they want/need to keep the price down.
Plaster is often thought of as being better than drywall. You'd pretty much need to price both repair and replacement to know the costs. Sometimes drywall gets installed over plaster, the main thing is to make sure the screws are long enough to secure the drywall to the ceiling joists.

 

If there is some compelling reason to keep the original fabric of the house then it can be plastered. There are some considerations about plaster and nailing the lath or using woven wire reinforcement over the lath or light gauge expanded metal lath. If there is no strong reason to keep plaster then remove the lath. The joists are probably not straight. The plasterer made that happen with plaster so you might need to run some strings and ad shims before installing the drywall. Yes you can blow insulation onto the drywall after it is up, or you can use batts before you put the drywall up.

 

I'm trying to figure out how insulation is an issue. Normally the first floor ceiling is not insulated. The second floor is usually insulated from the attic. Is there no attic ?