Hello Every 1 ! I Am Getting Ready To Paint Most Of Our House Was Painted With Semi-gloss. Can I Just Paint Eggshell , Satin Or Semi-gloss Finish Over It Or Do I Have To Prime It First? Please Let Me Know. Thanks Al;ot For Your Help......
We could use some more data here... If the house was built in the early '70's, you MUST perform a check for lead content before doing anything. If you do have lead paint, do not, under any circumstances, sand or scrape it without consulting your state Health Dept.
Assuming the existing paint does not have lead in it, you must, at the very least, give the existing semi-gloss a "scuff-sand" to rough up the surface. You aren't trying to remove paint here, just give some "tooth" to the existing paint. Then remove the sanding dust. If the existing paint is oil-base, you need to then prime with a quality water-base bonding primer or an oil-base primer. (I use SW PrepRite Pro Block Latex for this.)
Once you have done all that, you should be good to go to topcoat with the quality paint-store (not BigBoxCo) paint of your choice. Choose paint at or near the top of the product line.
As a side note, it is unusual to paint a ceiling with anything other than flat paint. While there are of course no hard-and-fast rules, ceiling light fixtures will tend to bring out any imperfections in the surface. Flat paint helps to hide this somewhat.