Is it okay to paint Satin over semi gloss paint?

You need to sand to give some tooth to the surface for the new paint to stick. You can also use Liquid Sandpaper and wipe it on and off.

As long as they are both water base I don't see a problem.

Yes....but I would lightly sand the semi-gloss first to make sure the satin finish will adhere properly. You may also want to consider using a coat of primer between them for better results.

Yes. You should wipe it down before repainting with a liquid sander. Just to dull the finish without scratching it.

Can I just use a satin with primer paint without sanding

Can I paint over semigloss with a statin with primer

It depends on the satin paint you are using to paint over the semi-gloss.

It also depends on the base semi-gloss.

Some paints are paint and primer in one. However; those paints are only designed to etch water based paints.

If the semi-gloss is really old (pre 2000) it could be oil. You can test the semi-gloss with oil based goof off. If the semi-gloss dissolves on to your rag, it's water based. Buy paint/primer in one - no need to prime first.

Some deglossers only work on water based paints, so be cautious with those.

I'd even use caution when 'sanding first'. If the semi-gloss turns out to be oil based and the walls are textured, you'll never be able to sand it everywhere.

Oil based semi-gloss is NO JOKE.

If you have to prime over oil. Read the label carefully. Some primers aren't designed to etch oil based paint.

Both Kilz and zinser make good primers but not all of there products are equally suited to the task.

You need to give the new paint something to adhere to so give it a light sanding.

Thank you for the advice.