“Should we build the villa on one floor or two?” comes up in almost every first design meeting. And the answer you usually hear is one of two: “two storeys looks smarter” or “one storey works out cheaper”. Both may be true, but neither is a calculation.
We don’t quote prices here, because prices change every few months. Instead we work out what doesn’t change: how many square metres of what each option needs. You can ask the price of a square metre any day; the quantities you only need to understand once.
A simple example: two 200 m² villas
Put two 200 m² villas side by side, each storey 3 m high, no basement:
- Single-storey: a plan 20 by 10 metres.
- Two-storey: two floors, each 10 by 10 metres.
| What | Single-storey | Two-storey | Difference |
|---|---|---|---|
| Area under the building (foundation and ground floor) | 200 m² | 100 m² | Two-storey: half |
| Roof, if flat | 200 m² | 100 m² | Two-storey: half |
| Roof, if pitched at 30° | about 231 m² | about 115 m² | Two-storey: half |
| Outside walls (facade) | 180 m² | 240 m² | Two-storey: 33% more |
| Structural intermediate floor | none | 100 m² | Two-storey only |
| Stairs | none | yes, on both floors | Two-storey only |
| Total envelope (floor + roof + walls) | 580 m² | 440 m² | Two-storey: 24% less |
Calculation: wall area = plan perimeter × height (60×3 and 40×6); pitched roof area = plan area ÷ cos 30° (factor 1.155).
The table isn’t the answer, but it shows the right question: which of these square metres are the expensive ones on your land and in your climate?
Where two storeys win
Foundation and ground floor: half
On the Babolsar and Sarkhorud coast, where groundwater is high, every square metre of building in contact with the ground means waterproofing and details that have to be done right. A two-storey villa halves that area. Why it matters so much on coastal land is explained in high groundwater and foundations.
Roof: half
In the north, the roof is the costliest part of a building to keep up: heavy rain, pitch, covering and roof-space ventilation. For the same floor area a two-storey villa has half the roof: half the covering, and half the surface someone has to climb up and check every few years. The roof criteria are in pitched roof or flat roof.
Envelope: 24% less
The heat a building loses in winter and gains in summer passes through its envelope. The relationship is simple: heat flow = area × thermal transmittance × temperature difference (Φ = A × U × ΔT). With the same insulation, a smaller envelope means less heat flow. In our example, the two-storey envelope is 24% smaller.
Source: Thermal transmittance (U-value) — Wikipedia
That’s a simplification, since roof, walls and floor have different U-values, but the direction is clear.
Land: more garden
For the same floor area, a two-storey villa covers half the land. On a small plot, that’s the difference between having a garden and not. The maximum site coverage is set by the local detailed or village plan; ask the municipality or village council before design.
Where one storey wins
No intermediate floor, no stairs
A two-storey villa has 100 m² of extra structural floor that has to carry the upper storey, and a staircase that takes a slice of floor area on both levels. In a single-storey villa, that floor area goes to rooms and living space.
Facade: a third less
The single-storey villa has 180 m² of outside wall; the two-storey has 240. In a humid climate, a facade isn’t just a building cost but an upkeep cost too: every square metre that soaks up water passes damp to the wall. Choosing its materials is covered, with figures, in facade materials for a humid climate, and the more facade you have, the more that choice matters.
One level for everyone
A villa that’s meant to last will one day host grandparents, or a toddler who’s just started walking. One storey means not a single step from the front door to the bedroom. Not having to haul suitcases upstairs every time doesn’t show up in any table, but it’s real.
Where they don’t differ at all
In this example, both are Group A buildings: under Part 2 of Iran’s National Building Regulations, a one- or two-storey building up to 600 m² falls in this group, so the engineering requirements and designer qualifications are the same for both. But the same Part says each factor “on its own” sets the group, so if you’re tempted to add a third storey halfway through, the building moves to Group B. The full group table is in our guide to choosing an architecture firm.
Source: National Building Regulations, Part 2 — Administrative Procedures; building groups in Part 2 (Persian)
So which one?
| If… | The scales tip towards |
|---|---|
| your plot is small | two storeys — covers half the land |
| groundwater is high | two storeys — half the area in contact with the ground |
| heating and cooling bills matter to you | two storeys — smaller envelope |
| the plot is large and the facade you want is expensive | one storey — less outside wall |
| elderly people or small children live there | one storey — no stairs |
| every square metre of living space counts | one storey — no stair area |
And one point outweighs both: most extra building costs are decided on paper, not on site — as we said in design mistakes that raise building costs. And don’t forget that some costs have nothing to do with the drawings at all.
In short
For the same floor area, a two-storey villa has half the foundation, half the roof and a 24% smaller envelope; a single-storey villa has a third less facade and needs neither an intermediate floor nor stairs. Which one works out cheaper depends on which of those square metres cost more on your land and in your climate.
This example is simplified (rectangular plan, equal heights, no basement); for your own plot, the comparison needs the real plan. If you have land in Babol, Babolsar or Sarkhorud and want to see this comparison for it, get in touch.
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