Can I paint over oil base exterior paint with a latex paint?

Answer Yes, you should be able to use a top quality exterior latex paint over oil based paint, if the surface is well prepared. (However, if the old paint consists of a buildup of say 5 or more coats of old oil paint, the safest approach is to continue with oil, because the latex paint can lift the old oil paint if not adhering well.) All dirt, mildew and loose paint should be removed. Sand any glossy areas to eliminate the gloss and get maximum adhesion from the new paint. NOTE: do not sand or otherwise remove any old paint if it may contain lead. Call the EPA at 1-800-424-LEAD for guidance. Some quality exterior latex paint may be applied directly to clean, sound oil-based paint; but check the product directions, as some manufacturers will require a primer, either latex or oil-based.