At every joyful occasion, you must do something to remember the churban Bais Hamikdosh. (MB intro.) After the destruction of the Bais Hamikdosh, Chazal decreed the following:
When finishing a house, leave a space the size of 1 ama by 1 ama unplastered or unpainted opposite the entrance so you can see it as you enter. There are those who leave the ama above the door inside so they can see it while they sit inside. (MB 2, 3)
If you will cover the walls with drapes, leave an ama without the drapes. (MB 3)
Painting an ama of black opposite the door does not count. But some places write over the black paint the words “zecher l’churban.” (MB 3)
If you buy a finished house, you are not obligated to peel away an ama of the wall unless the seller was a Jew who did not leave an ama. (ShA 1 – MB 4)
When preparing a seuda for guests, leave out one platter that would befit the seuda from the buffet table zecher l’churban. This applies even to a seudes mitzva but not on Shabbos and Yom Tov. (ShA 2 – MB 5)
When a lady bedecks herself with gold and silver jewelry, she should leave out one so it should not be a complete set. This applies on Shabbos and Yom Tov as well. (ShA 2 – ShaH 13)
Women who adorn themselves to the hilt cause great troubles because they arouse the jealousy of the gentiles. (MB 8)
A groom places ashes on his head where the tefillin go. (ShA 2)
Someone should smash a glass during the chuppa or place a black cloth over the head of the chosson. This is meant to shock the crowd and remember that we can’t have perfect simcha these days. This is also the reason to break a pot at the writing of the t’noyim. (Rama 2 – ShaT 3)
Playing or listening to instruments and sound makers of any sort for enjoyment is forbidden. This includes singing where wine is served. The Rama holds that without wine you may play as long as you don’t do so regularly like people who wake up and go to sleep to music or have music at every meal. Do not protest as long as they also serve food. (ShA 3 – MB 13 – ShaH 23)
The Bach forbids singing even without wine. Do not protest if you know they won’t listen to you. (MB 13)
You are allowed to enhance words of praise and thanksgiving with song. So it is a mitzva to sing in shul on Yom Tov. But if your main intention is enjoying tunes with your friends and you make the lyrics out of pesukim of Tanach, it causes the Torah to mourn and complain. (ShA 3 – MB 14)
You are allowed to sing a child to sleep. (ShaH 25)
A woman must not sing when other men are in the house. (ShaH 25)
The Sh’la warns not to sing romance songs. They arouse your yetzer hora and cause an evil nature for children who listen to them. Warn your family about this. (ShaH 25)
Do not sing on Shabbos except those zemiros that were fixed for the seuda. (MB 14)
For mitzva needs (e.g. for a chosson and kalla) there are no music restrictions. Still, don’t go overboard with simcha. (Rama 3 – MB 16)
A Kalla should not wear a veil with a crown of silver or gold. (MB 18)
It is forbidden for a person to fill his mouth with laughter in the present state of the world. Even at a wedding or on Purim. Besides, it can cause one to forget mitzvos. (ShA 5 – MB 20) ###
