Your half-bath is plumbed for only two fixtures and therefore probably
only has 1/2" supply lines.
These will have to be replumbed from the nearest 3/4" hot and cold
supply lines with 3/4" to the bathroom to add a shower.
A shower will require a 2" trap and drain, vented after the trap to the
main drain/waste/vent stack. If the half-bath doesn't have an exhaust
vent, you also should add one. Showers put out a tremendous amount of
moisture.
The expense and difficulty of this depends on your type of pipes
(supply and drain), how much wall and/or ceiling demolition you need to
do the plumbing, the remodeling that is necessary, and the shower unit
that you choose. Adding a shower bath is a good investment, as
bathrooms and kitchens have the highest return whenever the house is
sold.
Before you do anything, contact your Building Inspection Department for
local codes, permit and inspection requirements. Do NOT do this without
a permit.
You may be required to use a licensed plumber and maybe a licensed
electrican because you may well run into electrical lines in the walls
or have to add an exhaust vent. Depends on local codes. You can do all
demolition yourself. If allowed, you can do all of the other work, and
we'll be glad to help you with it.
Good luck!




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THOMPSON