Re: Volume or Pressure?
No, you don't need to replace all the 1/2" lines; that is a plenty big enough size. I would suspect another restriction in the line, such as a shutoff valve somewhere in the lines.
No matter what the size of the pipe, you'll always get that same STATIC pressure reading if there is no water flowing anywhere in the house. A more meaningful test is to check the pressure at the showerhead while you run various faucets around the house (remove aerators first). That can help pinpoint the problem. For example, if the washing machine causes the pressure to drop but the kitchen faucet doesn't, that can indicate that both the shower and the washing machine are downstream of the blockage but the kitchen faucet is upstream.
Do you have a pressure regulator? Sometimes those can cause this issue, but usually for the whole house.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.