One of the most common things clients do is bring drawings of a villa they admired in Lavasan or Fasham and ask for the same thing in Babolsar. The result is usually a house that looks the same but does not behave the same — and whose problems surface a few years later.
The difference between these two climates is not a matter of taste. It is numbers:
| Tehran (Mehrabad) | Amol (Mazandaran) | |
|---|---|---|
| Annual rainfall | 230 mm | 671 mm |
| Rainy days per year | 79 | 114 |
| Mean relative humidity | 40% | 78% |
| Climate classification | Semi-arid to arid | Semi-humid |
Roughly three times the rain and twice the humidity. These figures come from the Mazandaran Meteorological Office and the Mehrabad station record. Here is what each of them actually changes in the design.
1. Humidity is the governing problem, not temperature
In Tehran the governing design problem is temperature difference: hot summers, cold winters, and a wide daily swing. The architectural answer is thermal mass, insulation and solar control.
In the north, the governing problem is moisture. At a mean relative humidity of 78%, a building that cannot move air traps that moisture — producing mould, stale air, material decay and premature ageing. Heating and cooling do not solve this. Designing for airflow does.
This is why natural ventilation in the north is not a luxury feature but a technical requirement. At Villa 425 in Khazarshahr we deliberately elongated the plan east–west to increase the building’s exposure to the airflow running from the shore toward the forest and to create suction and pressure zones. That elongation was not a formal decision; it was the instrument of natural ventilation.
2. The rain is not just heavier — it is more frequent
114 rainy days a year is roughly one day in three. That figure matters more than the rainfall total, because it means surfaces never get a long spell to dry out.
The design consequences are direct: a pitched roof stops being a stylistic preference and becomes a functional necessity. Roof overhangs and canopies have to be taken seriously so water does not run straight down the facade. Rainwater routing and drainage must be designed in, not added afterwards as gutters. We covered this separately in the role of water in architecture.
Vernacular architecture here solved exactly these problems centuries ago: simple pitched roof forms that avoid snow-catching corners, the veranda and talar as intermediate space, and raised plinths to lift the building off wet ground. None of it was decoration.
3. The ground underneath is different
This is the most expensive difference, and it does not appear on any drawing. A high water table and soft clay and alluvial soils in the north behave in ways that directly affect foundation type and depth.
The practical consequence: a structural design prepared for a plot in Tehran is not automatically valid in Babolsar, even if the building above is identical. This is why we run internal soil mechanics and foundation engineering sessions, and why common villa design mistakes puts missing soil studies first.
4. Light is not the same commodity it is in Tehran
In Tehran sunlight is abundant and part of the design task is controlling it. In the north, cloud cover and humidity change the quality of light: it is softer and more diffuse, and its absence in the cold months is felt more.
So the ratio of glazing to solid facade follows a different logic. At Khorshid House in Babol we set that ratio so that the facade reads as though no solid wall exists — a decision that in the hot, sunny climate of central Iran would impose an unacceptable thermal load.
That freedom has a limit: in a humid climate every large glazed surface is a surface prone to condensation. The decision about light cannot be separated from the decision about ventilation.
5. Materials face a harsher test
Material durability at 78% humidity is not what it is at 40%. Details that are forgiving in Tehran — a joint that takes on a little water, a surface that dries slowly — become failures over time in the north.
That raises the stakes on facade material. At Aramesh Tower on Babol’s coastal boulevard we chose brick as the primary facade material — a choice that, beyond its sense of permanence, behaves more predictably in these conditions.
6. The relationship to the outside runs the other way
The traditional architecture of central Iran is introverted: a central courtyard, closed to the street. That was the answer to an arid, dusty climate.
In the north the logic inverts. Greenery, views toward forest or sea, and airflow are all reasons to open outward. This is why the veranda and talar are central to the region’s vernacular: a semi-open space that shades, keeps rain off, and does not sever the connection to outside.
A plan designed for a northern plot without this intermediate space has usually missed the site’s main opportunity.
So a Tehran plan cannot be moved north?
It can be drawn on for inspiration, but it cannot be executed. What transfers is taste and design language; what has to be solved again is plan orientation, ventilation strategy, roof pitch and overhang, water routing, opening ratios, facade detailing and, above all, the foundation.
In practice, once all of that is redesigned, little of the original drawing survives beyond the general idea — and it is better to know that at the start than halfway through.
If you own a plot in the north and have a design in mind, get in touch and we will look at which parts of it work in this climate and which need rethinking.
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