Regarding Halacha (Jewish law) as it relates to the time we're in, to these nine days, it's brought down that we do not perform binyan shel simcha. What is binyan shel simcha? It means home improvement or construction for the sake of a simcha (happiness). So, literally, that means if a new couple is getting married, we would not do any work on that house or apartment for that new couple during the week. Does that apply to anyone outside of a new couple? It does. And that is any one of us who is working on our home simply for the sake of simcha, which means you're making it nicer, changing the wallpaper, or doing something just to make it more enjoyable. We would not do that during these nine days, because it's for simcha.
Even though originally, binyan shel simcha meant chatan v'kallah (bride and groom), we understand it to mean all things that are similar, which are all building; that's for the sake of happiness. However, if someone is expanding their home or fixing up a room or something because they need to move into more space—they need that space—that's not considered simcha at all. That's considered necessity, and that we would do; we would perform during these nine days. But solely for the sake of more enjoyment, we would refrain during these nine days. That's a halacha. Have a great day.