Mechitza in Shul

Igros Moshe (OH I:39) Question To clarify the question the nature of the mechitza which is required in the synagogue between men and women, in particular the required height. That is because there are places in America where the observance of this halacha is deteriorating even though it is important for the sanctity of the synagogue. It is possible that this is not the result of a desire to sin but rather ignorance of the true nature of the obligation and its importance. Therefore it is important not only to know the details of the mitzva but its significance and nature. Answer  The actual law is that even if men are in one section and women in another it is prohibited that they not have a physical barrier between them and this in my view is a Torah law as can be seen from the gemora Sukkah (51b) that says that in the Temple that women were placed in a balcony over looking the court yard in order to separate the men and women. It is known that that no additions or modifications are allowed to the Temple. So obviously this balcony was an inherent part of the Temple as if it were written explicitly in the Torah and not Rabbinic or from the Prophets.  This is also alluded to in the Yerushalmi.  We see from the gemora Sukkah (51b) that even if there was a physical barrier between the men and the women but it was still possible that there would be levity between them there is still a Torah prohibition being violated. Don’t make the mistake to think the mechitza is needed just to prevent yichud (seclusion) of a man and a woman because with the large number of women present there was not a problem of yichud according to both Rambam and Rashi and in addition both areas were open to people entering which is better than a house that is open to the street. The main concern of the mechitza was to prevent levity between the men and women as the result of talking and contact between them. This was dealt with in the Temple by making a balcony above and behind the men  for the women. 

We can conclude from this that the synagogues where both men and women come to pray, it would be best to make balconies for the women so the women can be above. But if this is a problem for some reason it is necessary to make a mechitza (barrier) to prevent levity between the men and women. And It is not adequate just to have the doors always open.  This clearly means that a mechitza which is 10 tefachim high is not valid because it doesn’t prevent levity or prevent talking between the men and women or even contact. .In my opinion that it is sufficient if the mechitza is shoulder height . The prohibition is not to prevent the men seeing the women .