Rashi: The height of Sha'ar he'Chatzer interrupted the Aliyah. It did not surround the entire Chatzer. [The Aliyah] was flanks on both sides of the gate, corresponding to the height of the gates.

Radak: The Ritzpah on which the chambers were, it was past the gates, on each side. "Kesef" is side, like "vela'Kasef ha'Shenis" (Shemos 27:15).

Malbim: The Ritzpah was near Kesef ha'She'arim on each side, i.e. by the wall of the Ulam. It was six Amos thick, and 34 Amos long. The Ritzpah began and extended six Amos inside the Chatzer to the west. Only the Ritzpah was six wide, like the width of Kesef ha'Sha'ar, but the chambers were only four wide, and two Amos of the Ritzpah were empty of chambers. The window in the wall of the Ulam was in the Amah before Ayil ha'Ulam; the chambers did not block it.

Radak: The length of all gates was 50, and their width was 25.

Vilna Gaon: There were three floors, one on top of another. The bottom was (44 Amos), as long as the gate, i.e. 50, less the thickness of the wall (six).

Malbim: The length of the Ritzpah was along the length of the gates. I explained (refer to 40:15:6:2) that "Orech ha'She'arim" is from the beginning of the gate until the end of the cells. The Ritzpah was opposite this, inside. It was 34 Amos long, for the cells finished 40 Amos from the beginning ¹ of the gate. Correspondingly, inside the wall of the Ulam was six thick, and there were 34 Amos of Ritzpah. The Ritzpah ended opposite where the gate (i.e. the cells) ended.

Rashi: This "Tachtonah" is different than every other one in Tanach. Elsewhere, the accent is on the Nun; here it is on the [latter] Tav. It is not a Ritzpah under another ? rather, it is one Ritzpah at the height of the gate. The Hei at the end is extra, like the Hei in "Baisah" and "Ezrasah" (Tehilim 68:7, 44:27).

Radak (17-18): There was also an upper Ritzpah. The lower one was on the ground -"veha'Ritzpah El Kesef ha'She'arim" (17), and the upper one was on pillars ? a balcony. Perhaps it is like the balcony in Ezras Nashim (refer to 40:17:3:1).

Vilna Gaon: Refer to 40:18:2:2.

Malbim: Also the wall of the Chatzer ha'Chitzonah opposite the Ulam and Heichal had a Ritzpah and chambers, just like the walls of Chatzer ha'Chitzonah opposite Ezras Yisrael. The Ritzpah there in the north and south was called Ritzpah ha'Elyonah, for the Mikdash was on a mountain; the west was on top of, and the east was below (Tachton). Here it says ha'Tachtonah, lest we think that the calculation here includes the Elyonah. The Elyonah was not to the sides of gates ? there were no gates there!