In the context of the mitzva of ma’akeh, the Torah refers explicitly to a roof[3] and requires a fence of 10 tefachim (approximately 80 cm.).[4] However, any other dangerous area similarly requires a fence or covering, as appropriate.[5] Thus, the balcony in question would seem to require a proper ma’akeh.
Who is obligated to erect the ma’akeh, the landlord or the renter (you)? Regarding the question of who is responsible for seeing to a variety of needs of the house, the gemara[6] establishes a rule that a job that requires expert work is the landlord’s obligation, whereas simple work is the obligation of the renter. Ma’akeh is given as an example of the renter’s responsibility. Although the Pitchei Teshuva[7] cites two opinions on the matter, a renter’s obligation is apparently of Rabbinic origin, as according to Torah law, only the homeowner is obligated. Some explain that the reason the Rabbis transferred the Torah’s obligation of the landlord to the renter is the fact that the renter is more likely to fulfill his obligation promptly.[8]
Are there grounds to extricate you from the obligation? The Pe’at HaShulchan[9] makes a novel claim – that the landlord actually remains obligated to build the ma’akeh to begin with, and the gemara only means that if damage occurs to the fence, it is the renter who must take care of fixing it. However, this opinion is not accepted by most poskim.[10] The Rama[11] can be read as saying that local minhag determines who is obligated in ma’akeh, and we believe the minhag is that a landlord is expected to provide a safe dwelling, which would include a balcony from which there is no concern that someone might fall. However, this minhag might not apply when the balcony would generally be considered safe and is merely missing the halachic qualifications. In any case, if the landlord refuses to erect a halachically valid ma’akeh, you are likely obligated to do so.
Will setting up a situation in which you will rarely use the balcony help? The Rambam[12] rules that a ma’akeh is required only for a house that is lived in somewhat normally. Some infer from this that if one goes to his roof only infrequently, a ma’akeh is unnecessary. However, that approach is correctly rejected.[13] Only when the roof is not fit for use (e.g., it is steeply slanted) do we say that it is excluded from the obligation, but not when it is fit but just rarely used.[14] Only if one knows that he will not go to the roof at all, or if he makes it physically inaccessible, would the situation create an exemption. Otherwise, the occasional circumstances in which he will want/need to use the roof are enough to make the ma’akeh required. Note, however, that even if one is obligated to build a viable fence, it is not forbidden in the meantime to go carefully to the unsecured place.[15]
An important distinction between a ma’akeh for a roof and one for other places may be highly significant for you.[16] Whereas a roof bears an obligation for a formal ma’akeh (even if one could effectively minimize the danger in another way), what is necessary for other types of places is simply to practically remove the danger.[17] Thus, it is possible that a decision to rarely use the mirpeset, along with other factors, could create a situation in which there is no real danger, and you might then be exempt from constructing a ma’akeh. Of course, if the mirpeset is not safe, Halacha and common sense both dictate that one cannot leave the situation as is.
Therefore, it seems legitimate to be lenient and simply require that the mirpeset be safe, even if the official fence height is missing. You might anyway be able to raise the height to halachic levels in a way that is not very expensive, as a fence only needs to be strong enough to support the weight of a person leaning on it.[18]