A "payab" is a sloping gallery connecting the ground surface to the qanat gallery. This gallery has steps to make it possible for people to reach the water flowing in the qanat. The deeper the qanat the longer the payab. The slope of the payab is calculated so that the end of gallery meets the bottom of one of the qanat's shaft wells. The light was provided by the mentioned shaft. The size of a Payab stairway was such that two persons could go up and down side by side easily and their heads would not touch its ceiling. The payab was perpendicular to the direction of the qanat gallery in order to prevent the probable collapse of the gallery.
Inside the payab, the temperature is about 20°-25°C, cool compared to ambient summer temperatures,, due to its underground location and proximity to qanat water.
Some payabs were built for public use, near mosques, roads and caravanserais. But in some dry cities in central parts of Iran, many families had a private payab. The designers divided the qanat’s main branch into several side branches inside the city. Each side branch crossed part of the city and then at the other side of thecity, the side branches were joined to each other again. The houses neighboring the side branches had a private payab in which the owners rested during the hot days of summer. So, these houses were usually more valuable than other houses in the city. Also, there was a public payab in each part of the town for those who did not have access to a private payab, to use the water for sanitation. The payab structure was not complicated and the main part was like a room, which had a square or an octagonal plan with the following parts:
- There was a pool at the bottom of the payab. This round or polyhedral pool had some holes through which the qanat water entered or exited.
- Some platforms were constructed in the walls for people to sit on. There were more platforms in a public Payab than a private one. In the private Payabs, there were some shelves to put foodstuffs on. Also, there was a rope hanging from the ceiling above the pool, tied to a basket at the end to put some food, such as meat and fruit, to be kept fresh. The payab's roof was arched, resistant to collapse.